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AHo o o ,.., PROCEEDINGS
AUG 2 2 1991

of the
LJ A e^k / A r=>i-\

uiv San Diego Society of Natural History

Founded 1874

Number 6 i July 1991

Redescription, Ontogeny, and Demography of Parascothorax synagogoides

(Crustacea: Ascothoracida), Parasitic on Ophiophthalmus normani

(Ophiuroidea) in the Bathyal Basins off Southern California

Mark J. Grygier

Sesoko Marine Science Center, University of the Ryiikyt4S. Sesoko. Motohu-cho. Okinawa 905-02. Japan
Current address: I4H04 Noti'ey Road. Silver Sprini>. Maryland 20905. U.S.A.

ABSTRACT. — A lectotype is designated for the ascothoracidan Parascothorax synagogoides Wagin, and this species' host ophiuroid in the Sea
of Okhotsk is reidentified as Ophiophthalmus normani (Lyman). Both sexes off. synagogoides infesting O. normani in the bathyal basins of the
Southern California Continental Borderland are described, and a distinct post-larval stage is recognized. Parascothorax is distinguished from
Ascothorax mostly by plesiomorphies. and ontogenetic variability in male Parascothorax makes the previous use of male features in diagnosing
species oi Ascothorax unreliable. Three brooded naupliar stages corresponding to at least five instars are described, as well as the first- and last-instar
ascothoracid larvae. The parasite's cyst, which partly blocks one of the host's bursal openings, develops principally as a proliferation of the host's
genital bar; as the cyst grows, it becomes perforated and finally breaks open, leaving a permanent scar. The overall infestation rate in over 1 5,000 O.
norma«( collected off southern California was 5.0% (an underestimate due to missed small cysts) and ranged from 0.5% in the Tanner Basin to 9.0%
in the San Diego Trough. Multiple infestations were more common than expected by chance; in double but not triple infestations, bursal openings
flanking the same arm were preferred. Most cysts housed one female, nevermore, and zero to five males and/or last-instar ascothoracid larvae, the
latter often being ready to molt into post-larval males. Most males apparently join females when the latter are small and the cyst is not yet closed.
Brood sizes ranged from 3 to 183 depending on the female's size; individual broods were synchronous, and evidence suggests that females have
more than one brood. A hyperparasitic cryptoniscid isopod infested P. synagogoides with a prevalence of 1.5 to 15.4%; female isopods prevented
brood deposition. These demographic findings are compared to published data on two species of Ascothorax and a chordeumiid copepod that are
bursal parasites of other ophiuroids.

INTRODUCTION ascothoracidans, and the only large-scale autecological survey has

been that of Brattstrom (1947) on Ulophysema oeresundense

Superorder Ascothoracida. — The ascothoracidan crustaceans Brattstrom. which infests Scandinavian heart urchins,

are parasites of echinoderms and anthozoans. About 90 species in I have had the opportunity to examine a large collection of an

five families have been described worldwide (Grygier, 1987d). ascothoracidan found off southern California that belongs to the

They are characterized primitively by a bivalved carapace enclosing genus Parascothorax, and to collect it alive. This has provided not

the body, a pair of large, grasping antennules, piercing mouthparts only material for a taxonomic description, but also for rearing the

enclosed in an oral cone, six thoracomeres and six pairs of biramous larvae, observing the parasite's behavior and its effects on its host,

thoracopods, and a five-segmented abdomen with a penis on the and documenting its population structure and demographics. All

first segment and large furcal rami on the last. There are trends these subjects are treated in the present paper, which I hope will

within the higher Ascothoracida for the females to undergo reduc- serve alongside Brattstrom 's as a benchmark for biological studies

tion of the thorax and abdomen, including simplification or loss of on ascothoracidans.

limbs, with a concommitant increase in the relative size, morpho- Parascothorax. — This is a monotypic genus in the ophiuroid-

logical complexity, and presumably physiological importance of infesting family Ascothoracidae, part of the order Dendrogastrida,

the carapace, within which the eggs and larvae are brooded. There which includes most of the ascothoracidans with echinoderm hosts,

is also a more or less pronounced sexual dimorphism, often mani- Parascothorax synagogoides Wagin was first reported to infest

fested in the dwarfism of males, except in the one hermaphroditic Ophiiira qiiadrispina Clark at a depth of 1197 m in the Sea of

family. No complete life histories are known, and information about Okhotsk, where 57 of 270 examined ophiuroids were infested

settlement and metamorphosis is especially lacking. In most genera (Wagin, 1964). Unfortunately, the original host was misidentified;

brooded and sometimes planktonic nauplii are known (Grygier, following my inquiry Dr. I. S. Smimov has reidentified 12 infested

1987b), followed by less extensively documented bivalved ophiuroids from the parasite's type lot in the Zoological Institute in

ascothoracid larvae. There have been few biological studies of LtnmgraA as, Ophiophthalmus {= Ophiacantha) normanHLymim).

Mark J. Grygier

Wagin described females and dwarf males living within perforated
cysts that occlude the host's bursal openings. He considered
Parascolhora.x morphologically intermediate between generalized
ectoparasitic species now divided betv^een Synagoga and Waginellci
in the family Synagogidae and the more advanced genus
Ascothorax. which also infests ophiuroids. In this context Wagin
(1964, 1970) also discussed the historical biogeographical signifi-
cance of Parascothorax.

Rokop (1975) noted a low prevalence of an ascothoracidan
parasitizing O. normani in the San Diego Trough, a bathyal basin
off southern California. This species of ophiuroid occurs in the
North Pacific from the Gulf of California to Japan at depths of
roughly 70-3000 m (Clark, 1911; D'yakonov, 1967). In the South-
em California Continental Borderland, a topographically complex
regime of islands, ridges, and bathyal basins (Fig. 1 ), O. nornuini is
by far the dominant epibenthic organism in at least the Catalina
Basin (Smith and Hamilton, 1983), as well as an important animal
in the San Diego Trough. Rokop's parasite proved to belong to
Parascothorax, and I have already remarked on its sexuality, de-
scribed the larval ontogeny of its antennules, and briefly summa-
rized its occurrence and host relations (Grygier, 1987a, 1987b,
1988). A comparison with type specimens from the Soviet Union
shows that the Califomian form is also P. synagogoides.

METHODS AND MATERIALS

Soviet specimens. — I found twelve specimens of
Ophiophthalmus normani bearing multiple cysts and labelled in
Russian in V. L. Wagin 's handwriting as "Parascothorax
synagogoides. Sea of Okhotsk, 1949, Ushakov" in the Zoological
Institute in Leningrad in 1989. These I assume to be syntypes. I
borrowed one of these ophiuroids, with two cysts and the enclosed
parasites in good condition, for detailed study. Another infested O.
normani with five cysts (misidentified as Ophiura qiiadrispina; one
cyst opened and a female parasite displayed separately) is housed in
the teaching collection of the Department of Invertebrate Zoology at
Leningrad State University (.shelf A8). Wagin had deposited this lot
in the Department many years before he published his description of
P. synagogoides, and it bears a manuscript name, "Ascothorax witjasi
n. sp." I consider this another lot of syntypes of P. synagogoides.

Califomian specimens. — The Scripps Institution of Oceanogra-
phy (SIO) Benthic Invertebrate Collection houses many sorted lots
of Ophiophthalmus normani [see Luke (1982:34—35) for catalogue
numbers and detailed collection data] as well as unsorted trawl
samples containing large numbers of this species (Table I). They
were collected between northern Mexico and Big Sur (32°25'-
35°37' N), mostly in the various bathyal basins of the Southern
California Continental Borderland (Fig. I ), and from the southem
half of the Gulf of California (25°l7'-27°43' N), at depths of
approximately 900-1900 m by various investigators between 1951
and 1981. A few additional samples collected in the Catalina Basin
by K. L. Smith and colleagues were made available. All these
.samples, comprising 15,373 individuals of O. normani. were sur-
veyed for infestations of P. synagogoides; in large samples, aliquots
of 200-800 individuals were examined. All the ophiuroids with
evident Parascothorax cysts were isolated, and the number of
cysts, including broken, healed ones, was noted. In the earliest stage
of the study, small numbers of other species of ophiuroids may
inadvertently have been counted as uninfested O normani.

Wet and dry collections of Ophiophthalmus normani (labeled
Ophiacantha or Ophialcaea nornuini), taken by the U.S. Fisheries
Steamer Albatross between southem Califomia and Japan and
housed in the National Museum of Natural History, Smith.sonian
Institution, were examined for additional distribution records of
Parascothorax.

Living specimens. — I obtained living specimens of
Parascothorax .'synagogoides for laboratory rearing of larvae and
observations of behavior from an otter-trawl sample consisting
mostly of O. normani taken on 19 Mav 1982 in the San Diego
Trough, 33°35.5' N, 117°30.0' W, at a' depth of about 1200 m.
Twenty-six ophiuroids bearing large cysts were placed in seawater
slush for transport to the laboratory (about 10 hr), where they were
transferred to Whatman #2-filtered seawater at 8°C. When I re-
moved the parasites from their cysts four days later, I found living
individuals in 21 ophiuroids, dead ones in three, and only healed
cysts in two. The living females and males of Parascothorax were
kept in a refrigerator in a large bowl of filtered seawater, occasion-
ally changed. Many died during the first three weeks after capture,
but about one-third of the males and one-quarter of the females
were still alive on 18 July 1982, two months after capture, when
they were preserved. Escaped eggs and larvae from females" brood
chambers were tranferred at intervals to a separate bowl; subcul-
tures of offspring were maintained in petri dishes of filtered seawa-
ter. Nauplii did not molt in culture except for some late metanauplii
that molted to the first-instar ascothoracid larva; some of the latter
isolated into a subculture were still alive on 26 July 1982 (9.5
weeks), when they were preserved.

Demography. — A detailed survey was conducted on the largest
available SIO samples (E1439, E1668, E1782. R7139, R7145) and
one small one (R7128). El 439 was from the Catalina Basin, and the
others were from the San Diego Trough. With an ocular micrometer
I measured the radii of the ophiuroid discs (mean distance from
center to interambulacral margins), the diameters of the cysts in the
direction parallel to the bursal slit, the carapace widths of the
female parasites (no allowance made for distortions; newer stage
measured in molting specimens), and the carapace lengths of males
and/or last-instar ascothoracid larvae that accompanied the females
(newer stage measured in molting specimens; both stages measured
in ascothoracid larvae molting to post-larval males). The repro-
ductive state of the females (immature, gonads visible in carapace,
or brooding), the number and type of progeny present in the brood
chamber (eggs, embryos, or nauplii of three distinguishable stages),
and the incidence of hyperparasitic cryptoniscid isopods were also
noted. Nauplii were easy to count, but undeveloped eggs were very
fragile and could not be separated for counting without damage;
therefore, numbers of eggs were often estimated. For each multiple
infestation, the spatial relationship of the affected bursal slits was
noted. This detailed study revealed previously unnoticed sites of
infestation, usually involving very small cysts, on ophiuroids al-
ready known to be infested. Therefore, one lightly (E2125) and two
heavily (E1668, R7139) infested whole samples were reexamined
for additional infested hosts, and any additional data were logged as
described above.

DESCRIPTION

Parascothorax Wagin, 1964

Diagnosis. — Carapace of female a rounded pentagon in dorsal
view, with T-shaped array of longitudinal and transverse grooves;
pair of lappets flanking antennules. Four setae and two teeth on
antennular chin; antennular claw movable; claw guard with two
setae and up to two small spines. First three thoracomeres in females
with transverse ridges, fourth and fifth with smaller medial humps.
Filamentary appendages short, conical. Round lateral swellings at
bases of several thoracopodal coxae; coxa of sixth thoracopod
produced into large, rounded plate. Epaulets knob-shaped. Older
males with more than four terminal furcal setae. Parasites in cysts
formed from genital bar and bursal wall of ophiuroids.

Redescriplion, Ontogeny, and Demography of Parasco/hora.x synagogoides

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Type species. — Parascolhorax synagogoides Wagin, 1964, by
monotypy.

Remarks. — Species of the other genus in the family
Ascothoracidae, Ascothorax, live entirely within their hosts" bursal
cavities. Gi^gier (1983) remarked on the difficulty of telling
Parascolhorax from Ascothorax without knowing whether a cyst
was formed. Wagin (1964) proposed discriminative features that
are inadequate (Grygier, 1983), and though the diagnosis above
includes a few more features, doubts about the distinctness of
Parascolhorax remain. Ascothorax pilocaiidatus Grygier has a pair
of vanes on each of the first three thoracomeres, and its males have
more furcal setae than is usual in the genus, both features reminis-
cent of Parascolhorax. Ascothorax brattstroemi Grygier has little
thoracic expansion and no elaborations; its sixth thoracopods have
enlarged coxae, as in females of Parascothorax. Most species of
Ascothorax lack seminal receptacles in the second thoracopods
(Grygier, 1983). Morten.sen (1936) reported "a heavily plated cyst.
opening through a pore in the ventral interradius" of Amphiura
helgicae Koehler that enclosed Ascothorax hulbosiis Heegaard, but
Heegaard ( 195 1 ) did not mention such a cyst when he described the
species, just that the parasites were in a bursa. The dorsal groove
gives P. synagogoides an incipiently lobed carapace. A better de-
veloped, bilobed brood chamber occurs in Ascothorax ophioctenis
Djakonov and the undescribed /lie of/!o/a.v sp. B of Grygier (1983).

Wagin (1964) considered Parascothorax a grade of organiza-
tion intermediate between Synagoga and Ascothorax. In fact, it is
organized in much the same way as is Ascothorax but has anten-
nules slightly more generalized and better armed and a thorax less
hypertrophied than in most species of Ascothorax. No small spines
are recorded from the antennular claw guard of any species of
Ascothorax, and though one of the teeth on the fourth antennular
segment's chin in A. gigas Wagin and A. sosci Grygier is bifid (the
medial and the lateral one, respectively), no vestigial seta on the

medial side of the chin, like that of Parascothorax. is recorded in
any species of that genus (Grygier, 1983: Grygier and Fratt, 1984).
Since these morphological differences are plesiomorphies. it is
primarily the effect on the host and secondarily the carapace mor-
phology that lead me to retain Parascothorax as a separate genus.

Parascothorax synagogoides Wagin, 1964

Diagnosis. — As for genus.

Type material. — Lectotype female 3.3 mm wide, allolectotype
male 0.7 mm long, here designated (ZIN 1/66582), from the same
cyst in one of 1 2 specimens of multiply infested Ophiophthalmus
normani in the Zoological Institute, USSR Academy of Sciences,
Leningrad, collected by A. 1. Savilov and P. V. Ushakov, "Vityaz""
sta. 114, Sea of Okhotsk, 52°02'N, 147°58' E, depth 1197 m, 1947.
1 designate as paralectotypes the remaining specimens of P.
synagogoides from these 12 ophiuroids and those housed in the
Department of Invertebrate Zoology of Leningrad State University
(display shelf A8, labeled "Ascothorax witjasi n. sp.'").

Other material. — Hundreds of female and male specimens,
some of the females brooding offspring, obtained from southern
Califomian Ophiophthalmus normani (Table 1). Specimens from
the six samples studied in detail are in my possession; the other
infested but undissected ophiuroids are in the SIO Benthic Inverte-
brate Collection.

Califomian Females

Carapace. — The carapace is more or less globular, 0.41-3.85
mm wide, and at maturity is shaped like a rounded pentagon in
dorsal view (Fig. 2a); it is also rounded in most juvenile specimens.
The carapace's aperture occupies about 40% of the sagittal-circum-
ference; its margins are considerably thicker than the rest of the
carapace, and the anterior end of the aperture is flanked by a pair of

Mark J. Grygier

Table 1 . Infestation of Ophiophthabnus iwrmaiu by Parascothorax synagogoides in four
bathyal basins off soutfiem California, based on samples in the Scripps Institution of Oceanog-
raphy Benthic Invertebrate Collection.

Number of Cysts

Percent

Number of Cysts

Sample

1

>2 Infested Sample

Percent
Infested

Tanner Basin

e:i34

405

T

—

—

0.5

E2125

403

1

E2130

250

1

—

—

0.4

E2155

3.56

1

E2121

617

3

—

—

0.5

El 656

472

1

E2180

366

5

—

—

1.4

San Clemente Basin

E1641

1

—

—

—

0

El 747

65

4

El 750

9

—

—

—

0

El 649

7.36

20

B 17427

337

1

—

—

0.3

El 758

2

—

B 17427:

4Apr 1974, 33°05'N,

118°17-W,

1114 m.

Calalina B

isin

El 755

2

—

—

—

0

E352

158

3

E1789

227

3

—

—

1.3

E356

81

2

E1651

710

2

—

—

0.3

E683

350

1

E1439''

800^

59

17

4

10.0

SV

596

—

El 632

395

33

4

—

9.4

El 629

121

2

SX

427

2

—

—

0.5

Mil

635

59

SV: SABRAT V, 33°12'N. U8°08'W, 1050 m.
SX: SABRAT X. 23 Apr 1981. 33°35'N, 118°22'W, 1098-1116m.
Mil: MET II Sta. 103, 13 Jun 1981, 1350 m.
San Diego Trough

0.2
0.3

0.2

6.2

2.9

0

1.9
2.5
0.3
0
1.7
12.1

El 856

112

2

—

—

1.8

El 853

59

2

1

—

5.1

E1812

20

—

—

—

0

E947

3

—

—

—

0

El 866

20

3

3

—

30.0

El 663

778

27

2

—

3.7

£1782* 800''

62

12

6

10.0

R7120

200''

7

—

—

3.5

R7I28

' 191

4

6

1

6.3

R7137
El 668''
R7145''

260

32

1

2

13.5

R71,38

, 549

19

2

—

3.8

632

108

23

6

21.7

R7139

^ 396

50

10

—

15.2

748''

49

12

2

8.4

El 806

17

—

—

—

0

E1777

4

—

—

—

0

El 679

4

—

—

—

0

E2715

32

1

—

—

3.0

E638

56

2

—

—

3.6

El 446

35

3

—

—

8.6

SIV

108

3

—

—

2.8

R7120

18/19 Jan 1971.

32°27'N, 117°29'W, 1204-1

226 m.

R7128

21 Jan 197

,32

'35'N,

117°34'W.

1184-1217

m.

R7137

21 Apr 1971,32

°26'N

117°30'W

1098-

-\\9t

m.

R7138

21 Apr 1971,32

°34'N

117°30'W

1208

m.

R7139

12 Jul 1971

, 32°37'N,

117°33'W.

1162-

1199

m.

R7145

14 Jul 1971

,32'

25'N,

I17°27'W,

1208-

1244

m.

SIV:S

ABRAT IV,

12Augl980,32°25'N

, 1I7°41W

1100 m.

"Collection data for most samples were given by Luke ( 1982); data for those that were not are given
here. Additional samples from other localities were also examined: E1681, E1745, E1715, E612.
E626, E1814, E1760, E766, E1808, E1710, E1948, E2056, E1937, E2165.
Sample used in demographic analysis.

'Aliquot.

lappets that partly cover the antennules. The thin-walled dorsal
brood chamber is split by a longitudinal groove beginning above
the anterior end of the aperture and is bounded behind by a pair of
transverse grooves. A shorter anterior pair of grooves is sometimes
visible and is very clear in the lectotype. The ovary diverticula of
older females loop within the carapace from the side of the head to
the anterior pan of the aperture, then split into a short anterior and
long posterior branch parallel to the aperture (Fig. 2b). The gut
diverticula follow the ovary diverticula, with proximal branching
into the thin wall of the brood chamber.

Antennules. — The five-segmented antennules (Fig. 2d) reach as
far ventrally as the oral cone. The first segment forms a flat cup
applied to the side of the head. The second segment is as broad as
the first but shorter and is partly retracted into it. The distal three
segments are much narrower than the basal two. The third segment

is trapezoidal, longer than wide. The fourth is sector-shaped (Fig.
2e); its anterior chin has two strong apical teeth, a subapical pair of
short, vestigial setae on the proximal side, another such seta next to
the medial tooth (not always visible in mounted preparations), and a
fourth vestigial seta laterally on the distal side. The fifth segment
(Fig. 2e) is small, roughly square in side view, narrower than the
fourth, and is armed along its anterior edge with a stalked
aesthetasc, a seta, a short, stubby claw guard with two setae and up
to two small distal .spines (latter sometimes difficult to see), and a
movable claw with three vestigial setae at the base.

The antennular musculature, shown schematically in Figure 2d
(also valid for males), was previously illustrated by Wagin ( 1964:
fig. 7A), Most of the individual muscles cortespond to ones illus-
trated by Grygier ( 1987c: fig. 7A) in the six-segmented antennules
of a relatively generalized synagogid ascothoracidan.

Redescription, Onlogeny, and Demography of Parasiolhorax synagogoides

Figure 2. Parascothorax synagogoides, mature Califomian females, a, carapace, dorsal view; b. inner view of carapace valve; c. body of mature female;
d. antennule, lateral view, musculature shown schematically, including one muscle (?) not identifiable with any muscle in more generalized antennules; e,
distal antennular segments, medial view; f. thoracopod 1 and filamentary appendage; g, thoracopod 4 (also typical of thoracopods 2 and 3), showing
musculature, dashed muscles based on another leg; h, thoracopod 5; i, thoracopod 6; j. bases of thoracopods; k, most of abdomen, including musculature
(proximal muscles originating in first abdominal segment); 1, furcal ramus from another specimen. Thoracic, abdominal, and antennular segments and
thoracopods numbered. Scale bars 0.5 mm in a-c, otherwise 0.1 mm. ad, adductor muscle; an. antennule; eg, claw guard; ch. chin; cl. claw; e. eggs; ep.
epaulet; es, aesthetasc; fa, filamentary appendage; fr, furcal ramus; gd, gut diverticula; gp, genital pore; n, endopod; oc, oral cone; ov. ovary diverticula; p,
penis rudiment; sr. seminal receptacles; x, exopod.

Mark J. Grygier

Gorgnnolaureus muzikae Gr>'gier, but there are several differences.
In P. synagogoides but not G. muzikae the lateral extensor of seg-
ment 2 is divided, the extra part originating on the edge of segment
I. The lateral and medial flexors of segment 4. originating in
segment 2. are parallel, so differing from G muzikae. The more
proximal of the two muscles extending between the anterior edge of
segment 3 and the opposite proximal edge of segment 4 is not
readily identifiable with any muscle in segments 3 and 4 in G.
muziliae. The medial extensors of the last segment originate only on
the side of segment 4, none more proximally. The two claw retrac-
tors both originate from the sides of the last segment, not from the
medial side and proximal comer.

Mouthparts. — The oral cone is very small relative to the body
(Fig. 2c). and the mouthparts are like those of the males (cf. Fig.
4e). The labrum is open behind, the mandibles are long and slender
with setulate tips, the maxillules are short and blunt, and the maxil-
lae are basally united, w ith harpoon-like bifid tips. A pair of maxil-
lary-gland papillae protrudes from the base of the maxillae.

Thorax and ihoiacopods. — The thorax is moderately expanded
(Fig. 2c). The first thoracomere is distinct from the head. The first
three segments are usually broader than the rest, and each has an
anterior transverse ridge or flap that is sometimes interrupted at the
midline or ornamented with low lateral and medial processes. The
fourth segment often has a medial hump, and the fifth has a smaller
one. The sixth segment is unmodified except for a pair of knob-
shaped lateral epaulets.

There are six pairs of thoracopods. The first pair is uniramous
(no endopod) and bears short plumose distal setae (Fig. 2f). At its
base is a genital papilla and, usually sitting reflexed over the base of
the limb, a small filamentary appendage ending in one or two short
spines (Fig. 2f, j). Thoracopods 2-5 are leaf-like with the posterior
ones narrower (Fig. 2g. h); a tiny seta arises from the body wall just
above each limb insertion (Fig. 2j). The coxa is relatively shorter in
thoracopod 2 than in the other pairs, and the basis is shorter than
wide in all pairs. The basolateral part of the coxa has a round
proximal process on which the seminal receptacles open in
thoracopods 3-5 (Fig. 2j); there are fewer than 10 narrow elongate
receptacles per thoracopod, and they are usually or always absent in
thoracopod 2. The tapered, usually unsegmented rami are no longer
than the basis, with the endopod wider and slightly longer than the
exopod; occasionally two segments are evident, most often on an
exopod (Fig. 2g, h). Short plumose setae line the rami and the distal
parts of both edges of the protopod, more found medially than
laterally. The sixth thoracopods are flattened against the sides of the
abdomen; the coxa has a large, rounded, posterior plate covered
with short hairs (Fig. 2i), and the coxa-basis articulation is usually
indistinct; the rami are unsegmented and more densely setose than
those of the other thoracopods.

The musculature of thoracopods 2-5 (Fig. 2g) is simpler than
that illustrated by Grygier (1987c: fig. 7C) for the generalized
thoracopods of Gorgouolaureus muzikae. No lateral diagonal coxal
muscle was positively identified, and only one muscle was seen
reaching to the midlength of each ramus (6". muzikae has two).

Abdomen. — The abdomen has five unequal segments, the first
with a ventral penis lobe and the fourth with a moderate ventral
protrusion. The musculature is shown in Figure 2k. The straight,
tapered furcal rami are about three times as long as their basal
height and have 10-20 short, simple terminal setae and several
shorter, slightly lateral setae along the distal half or so of the ventral
edge (Fig. 2k-l); an occasional seta is bifid or trifid.

Post-larvae (Fig. 3). — The smallest settled females are consid-
ered post-larvae. While their carapaces are rounded, unlike the
laterally flattened ones of males, their bodies are almost exactly like
those of post-larval males (males described and illustrated below).
At that stage there are no differences between the sexes in the
antennules and oral cone. Both sexes have thoracopods with few or

no setae and no filamentary appendages, and the furcal rami are
only as long as the telson, with three or four terminal setae. I
observed a nub-like frontal filament in one female post-larva in
contrast to the longer filaments of males; older females seem to
have no frontal filaments.

Califomian Males

General features. — The carapace is bivalved, oval, and laterally
compressed (Fig. 4a). 0.47-1.34 mm long, and 0.75-0.90 times as
high as long. The valves are soft and flabby with clusters of internal
guard hairs along the free margins except anteriorly. The body
tagmosis is 5-6-5 if only limb-bearing segments are considered as
thoracic; the thorax is lightly arched, and the abdomen is U-shaped
(Fig. 4b, 1). The smallest males (post-larvae, see below) lack testes,
but larger ones have testes and short-headed sperm in the carapace.

Cephalic appendages. — The antennules consists of five seg-
ments, and segments 3 and 4 are immovably joined (Fig. 4c).
Segments 4 and 5 form a subchela (Fig. 4d) and agree structurally
with those of females in most respects. The chin is more pronounced
in the males, and the subapical pair of vestigial setae on its proximal
side is larger. The fifth segment's aesthetasc is somewhat longer
than the segment and appears to have a pore at its tip (pore also seen
in lectotype female; not a true aesthetasc?).

Antennae and eyes are absent, but a pair of frontal filaments
arises from the inner surfaces of the carapace valves next to the
antennules (Fig. 4c). The oral cone is like that of the females
(Fig. 4e) but much larger relative to the body (Fig. 4b).

Thora.x and thoracopods. — The thoracic segments are
unmodified dorsally, but the posterior ones are slightly longer, with
a pair of knob-like epaulets on the sixth segment (Fig. 4b). There
are six pairs of thoracopods. The first pair is shorter than the others
and is uniramous with one or two setae. The other five pairs are

Figure 3. Parascothora.x synagogoides. Califomian female post-larvae,
a. body removed from carapace, some thoracopods obscured, lYonlal fda-
ment added from another specimen: b, left thoracopods of another specimen,
ad. adductor muscle; an, anlennule: d. mandible: ep. epaulel: ff. frontal
filament; fr. furcal ramus; la. labrum: nil. niaxillulc: mx. maxillae. Scale
bars 0. 1 mm.

Redescription. Onlogcny, and Demography of Pcira.sailhorax synagogoides

Figure 4. Parascothorax synagogoides. Califomian males, a, carapace, lateral view, front end left; b, body of post-larva: c, antennule of mature male and
frontal filament; d, distal antennular segments, lateral view; e, oral cone; f, thoracopods of post-larva; g, thoracopods of medium-sized male, fine hairs
omitted except on one seta; h, thoracopods of large male, progressively more posterior from left to right; i, furcal ramus of post-larva; j-k, furcal rami of
mature males; 1, schematic diagram of abdominal musculature of young male, all illustrated muscles actually paired, proximal ones without arrows
onginating in sixth Ihoracomere. left one with arrow the ventral longitudinal muscle, ad. adductor muscle; an. antennule; eg. claw guard; ch, chin; cl. claw;
d. mandible; es. aesthetasc; fg, foregut; fr. furcal ramus; la. labrum; md. maxillary gland duct; ml. maxillule; mx. maxillae; n. endopod; oc, oral cone; ts.
testes; x, exopod. Scale bars 0. 1 mm.

Mark J. Grygier

biramous: the endopod is sometimes small in the sixth pair, but
otherwise the endopods are approximately equal to or slightly
shorter than the exopods. The rami are obscurely segmented, but
often two segments are visible. The setal armament varies with the
male's size (Fig. 4f-h). In the smallest males, there are just fine
hairs on the endopods and one simple seta on some exopods. In
medium-sized males, the edges of the thoracopods are hirsute and
each ramus has one or two plumose setae. Larger males additionally
have a lateral coxal and medial basal seta on the second and
sometimes third thoracopods. The largest males have up to four
plumose setae on the exopods of thoracopods 2^.

Abdomen. — The abdomen is five-segmented with a furca (Fig.
41). The first segment has a simple midventral penis lobe. The
fourth segment is short, the others subequal, and the fifth is broad-
ened posteriorly, with ctenate ventral scales. The furcal rami are
rectangular and elongate, shorter than the telson in the smallest
males, but otherwise at least 1 .5 times as long as the telson (Fig. 4i-
k). The lateral and medial faces of the rami have ctenate scales. The
smallest males have three or four terminal setae, and the largest
ones have ventral setae as well (I observed at most 13). The distal
halves of the furcal setae are pilose.

The abdominal musculature is shown diagramatically in Figure
41. All the described muscles are actually paired. Muscles insert at
the bases of the furcal rami dorsolalerally, ventrolaterally and
ventromedially. and at midheight medially: in younger but appar-
ently not in older males, a ventromedially inserting furcal muscle
arises in the fourth segment. Abdominal segments 1^ each have
one to three dorsal flexor muscles and one to three ventral exten-
sors. The ventral longitudinal muscles of the thorax insert
ventrolaterally in the first abdominal segment.

Post-larvae. — I propose that a distinct post-larval stage be rec-
ognized for the smallest males, which as yet have no testes devel-
oped, almost no thoracopodal setation, and furcal rami remarkably
small compared to those of larger males (Fig. 4b. f. i). As mentioned
above, aside from the shape of the carapace and the length of the
frontal filaments, male post-larvae are morphologically
indistiguishable from the smallest females, which I also term post-
larvae.

Adult Behavior

Living females exhibited little behavior. They could open the
carapace but not close it completely, so eggs and larvae readily
escaped from females removed from their cysts. They could abduct
and adducl their furcal rami and point the oral cone in different
directions. They usually beat the rear pairs of thoracopods. some-
times in a slow metachrony, but more usually in a less organized
manner with a simultaneous recovery stroke. Their most consistent
behavior was to extend the antennules ahead one at a tune from
below, opening the subchela when doing so. and then to retract
them, all in one continuous motion.

Males were immotile. However, the oral cone was in constant
motion, protruding and retracting and bending somewhat in all
directions. Males extended their antennules alternately straight
ahead, as did the females, with an open subchela that was clo.sed
before being withdrawn. The abdomen, usually curled under the
thorax, sometimes beat as an unstraightened unit with some motion
of the splayed furcal rami, but the furca and thoracopods did not
beat for locomotion.

Comparison to Types

Wagin's ( 1964) females of Pciiascolhora.x .tyiuiiiofioiih's aver-
aged 4 mm in diameter, and reached 6 mm (those I examined were
not so large), while the Califomian specimens are smaller than 4
mm. Wagin's males were 0.7-1.2 mm long, as are the Califomian

ones. Examination of the antennules of the lectotype (Fig. 5a, b)
and allolectotype (Fig. 5e, f) shows the same armament of the chin
and basically the same armament of the fifth segment, except that
both the male and the female probably have only one small spine on
the claw guard (variable in the Califomian material). Wagin ( 1964:
fig. 8E) confused the mandibles and maxillules and drew the former
as halves of a sucking tube lacking setules at the lips: he did not
draw the tips of the maxillules as bifid. In the type specimens the
maxillae are minutely bifid (Fig. 5c), but the tips of the mandibles
are hidden from view within the oral cone. The furcal rami of the
males have, according to Wagin, five to seven setae and a hairy
surface. The vertical grooves he drew on the lateral surfaces of the
rami are exaggerated (compare Fig. 5f and Wagin, 1964: fig. 9), and
the true sculpturing is a slightly weaker version of that of the
Califomian males (Fig. 4i-k); in the allolectotype not all of the
furcal setae are pilose. In all significant respects, therefore, speci-
mens of Parascothorax from Califomia agree with the original
specimens from the Sea of Okhotsk, and I consider them to repre-
sent the same species.

Post-larvae. — Grygier and Fratt (1984) proposed that the molt
at which natatory setae are lost be considered the end of larval
development. Now I have propo,sed that the early post-settlement
stage of males and females in Parascothora.x be considered a post-
larval stage. The male post-larvae are smaller than the settled last-
instar ascothoracid larvae (Fig. 6) but the same size as the males
that were about to molt from those ascothoracid larvae. The number
of instars in either sex after the metamorphosis to the post-larva is
unclear. Most of the preserved females examined, no matter what
their size, had loose cuticles, so females seem to have no terminal
molt.

Ta.xonomic remarks. — In males the marked changes from post-
larva to maturity in features such as size, thoracopodal setation, and
relative length of the furcal rami (Fig. 4f-h, i-k) suggest that these
features are probably variable and size-dependent in the closely
related genu?, Ascothorax. It is likely that most of the male charac-
ters employed by Grygier (198.'^) in diagnoses of species of
Ascothorax are unreliable.

LARVAL DEVELOPMENT

General remarks. — Wagin (1964) gave very little information
about the larvae of Parascothorax syngagogoides. However, an
ontogenetic sequence based in part on laboratory-reared larvae is
available for the Califomian population. Grygier (1987a) discussed
some aberrant, possibly female nauplii in connection with sex
determination; here only ordinary nauplii (possibly all males) are
discussed. The ontogenetic sequence includes brooded eggs, three
brooded naupliar stages not conclusively linked to instars and re-
ferred to here as nauplii. early metanauplii. and late metanauplii,
and at least two non-brooded cypris-like larvae, referred to as first-
instar and last-inslar ascothoracid larvae.

I estimated the number of naupliar instars by counting the
unshed exuvia of older larvae, of both cultured ones and ones
preserved upon capture, as I did for another ascothoracidan,
Gorgonolaiireus miizikae (see Grygier, 1987b). I have often found
brooded larvae with several nested, unshed cuticles in preserved
ascothoracidans, and I assume this to be nomial for this group. The
maximum replicable observation in P. synagogoides was five old
cuticles investing the ascothoracid larva ready to molt, so there
must be at least five naupliar instars.

All of the available first-inslar ascothoracid larvae were derived
from late metanauplii that molted in culture, usually one or two
days after release from a brooding female: none of these molted
again in culture. Since I never observed this stage being brooded, it
must appear in nature only after the metanauplii are released and

Redescriplion, Ontogeny, and Demography of Purascolhorax syna^ogoides

Figure 5. Parascolhorax synagogoides. type specimens from Sea of Okhotsk, a-d, lectotype female; a, whole animal with right carapace valve removed;
b, distal antennular segments; c. tip of oral cone; d, distal half of left furcal ramus (setae do not go so farproximally on right one); e-f. allolectotype male;
e, whole animal; f. body removed from carapace, ad, adductor muscle; an, antennule; eg. claw guard; ch. chin; cl. claw; e. eggs; ep, epaulet; es, aesthetasc;
ff, frontal filament; fr. furcal ramus; gd, gut diverticula; md. maxillary gland duct; mx, maxillae; oc, oral cone; ov, ovary; p, penis rudiment. Scale bars 1 mm
in a and b. otherwise 0. 1 mm.

undergo a final molt. I found last-instar ascothoracid larvae, all
apparently male, together with females as independent individuals,
never brooded, and they were often ready to molt to the post-larval
male. None bore an unshed cuticle of any earlier larva, and it is
unclear, though unlikely, whether any additional free-living instars
exist between the two known ascothoracid larvae.

E^gs. — Brooded eggs are spherical, dark red, and 440 |j.m in
diameter.

Nauplius (Fig. 7a-e). — The earliest larvae are rotund, almost
0.7 mm long, filled with yolk, and provided with a small protruding
labrum, two furcal and one terminal papillae, and no frontal fila-
ments or eyes (Fig. 7a, b). The antennules are unsegmented with the
setation lm-lm-2m.ll-2t (Fig. 7c). The antennae have a small
enditic spine on the coxa and a short medial protuberance on the
basis: the endopod is unsegmented with two terminal and often one
subterminal setae; the exopod is unsegmented with four or five
setae (Fig. 7d). The mandibles resemble the antennae, but the
protopod has only a small medial coxal flange, the endopod has no
subterminal setae, and the exopod has three to five setae in different
specimens (Fig. 7e).

Early melanauplius (Fig. 7f. g). — This larva has a kite-shaped
dorsal shield flatter than that of the nauplius. It is unclear whether
papilliform frontal filaments are present. The limbs are unchanged
from the nauplius except that the protopods are unarmed. Rudi-
ments of maxillules, maxillae, and the first two pairs of thoracopods
are apparent under the cuticle. The yolk mass is arrowhead-shaped,
pointing backward.

Late melanauplius (Fig, 7h-n). — The bowl-shaped dorsal shield
is 0.67-0.80 mm long and 0.5.'i-0.66 mm wide and is slightly in-
dented at the midline at both ends (Fig 7h-j); it contains the bivalved

carapace of the developing ascothoracid larva. Frontal filaments are
present, and the labrum is short and pointed. The unsegmented
antennules have new medial setae, and the apical setae are disposed
differently, so the setation is lm-lm-lm-2m.21-lt (Fig. 7k). The
antennal and mandibular protopods are unarmed, the endopods have
a terminal and subterminal seta, and the exopods are annulate with
six setae, the distal seta being short (Fig. 71, m). The maxillules and
maxillae are represented externally by a pair of knobs bearing two
bumps or spines each, and the thoracopods are represented by several
pairs of spinules (Fig. 7n). The furcal region is developed into a pair
of lobes protruding beyond the end of the dorsal shield, with cuticular
ctenae and four spines on each lobe; there is a tiny terminal spine.
Rudiments of all postcephalic appendages including the furca are
present beneath the cuticle (Fig. 7j). the medially unfused maxillae
being the largest and all but the first pair of thoracopods being
biramous. The yolk is confined to a small central mass with lateral
lobes corresponding to the future gut diverticula.

First-Instar Ascothoracid Larva

General features. — The carapace is bivalved, but the valves are
inflated with rounded edges and are held partly splayed, not fully
enclosing the main body (Fig. 8a). The valves are 0.67 mm long and
0..^9 mm high, with more or less straight dorsal and ventral mar-
gins, the anterior end higher than the posterior, and the dorsal hinge
line extending for over two-thirds of the total length (Fig. 8a, b).
The body is divided into a head, thorax, and abdomen (Fig. 8c).

Antennules. — The antennules are almost straight and indis-
tinctly segmented (Fig. 8d). The first, fourth, and fifth segments are
about as long as wide, and the second and third ones are shorter. The

10

Mark J. Grygier

20

15

10

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malel I
ascothoracidlarvaQ]

fu

E1439

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XI

0.5 1

Carapace Length [mm)

E1668

15
10
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E1782

n

n

0.5

Carapace Length [mm3

15

10

0.5 1

Carapace Length (mm)

R7145

0.5 1

Carapace Length Cmm)

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0.5

Carapace Length (mm)

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Figure 6. Size-frequency histograms of males and last-instar ascothoracid larvae from five samples oi Parascothorax synagoi-oides. The smallest males
are post-larvae.

anterior side of the fourth segment has a chin-like protrusion at
midlength with two basal setae, two apical spines, and a subapical
seta on the distal side. The claw on the distal comer of the fifth
segment has three setae around its base, and there are three setae on
the posterior side of this segment, the pro.ximal one longest and the
third one shortest and sometimes absent. The claw guard is twice as
long as the claw, with a small cylindrical tube proximally in most
specimens and two to four (usually three) short distal setae, one
longer than the rest. A frontal filament complex, consisting of a
knob and an aesthetasc, arises from the inner wall of each valve just
posterolateral to the antennules (Fig. 8e).

Mouthparls. — The labrum is a slightly curved triangular plate in
front of the other mouthparts (Fig. 8e). The antennae and mandibles
are reduced versions of the naupliar limbs, twice as large in freshly
molted specimens as in ones kept in culture for several weeks (Fig.
8c, e-g). The antennae are lateral to the labrum and the mandibles
arise behind them; both are biramous with vestigial setae on the
exopods and usually inconspicuous endopods. The mandibles have a
stout prolopodal endite formed cie novo and bearing an apical spine.
The maxillules are a pair of sharp cones medial to the mandibles
behind the labrum (Fig. 8c, e). and the unfused maxillae are behind
them and about twice as long, with bifid or trifid lips (Fig. Sc. e. h).

Thorax uiid llioracopods. — The six thoracomeres become
longer and slightly lower posteriorly, and the first is not separated
from the head by a suture. There are no elaborations or setae on any
segment, but the sixth has a pair of small epaulets (Fig. 8c). Each
segment has a pair of thoracopods with short setae, all except the
first pair being biramous (Fig. 8c). The first thoracopod is shorter
and much narrower than the others, with two distal setae and
occasionally a medial one. The next four thoracopods are much
alike but become somewhat shorter posteriorly: the elongate coxa

has a basolateral bump, the basis is square, the exopod is two-
segmented, and the endopod is three-segmented (segmentation
better defined in older larvae), with four temiinal setae on the
former ramus and three on the latter, the segments of the exopod
being nearly equal but the distal one on the endopod being longer
than the other two. The sixth thoracopod is the shortest, with a
proximal constriction in the posterior part of the coxa setting off a
"precoxa"; the two-segmented rami each have a longer second
segment, that of the exopod bearing three terminal setae, that of the
endopod bearing two.

Abdomen. — The abdomen is four-segmented and bent into a U,
with a pair of furcal rami not clearly separated from the last seg-
ment (Fig. 8c). The first and third segments are as long as wide,
while the the second and fourth are much longer, and the first
segment bears a rudimentary penis. The furcal rami are rectangular.
i..*! times longer than high and possessing some dorsal and ventral
spinules. usually a dorsodistal spine, and seven setae set into deep
pockets (probably three terminal ?nd four medial); all the setae are
about as long as the furcal rami.

Last-Instar Ascothoracid Larva

General features. — The carapace is bivalved with a distinct
hinge and sharp valve margins, about 0,67 mm long, 0.47 mm high,
0.29 mm wide (almost no variation; Fig. 6), and lenticular in shape
except for the rear being slightly more produced than the front (Fig.
9a). The outer cuticle has a weak polygonal pattern of ridges and
scattered conical pores; each valve also has two cardie organs (Ito
and Grygier. 1990). elongate pits with thickened rims, near the front
of the hinge and two more close together at the rear of the hinge.
The anterodorsal part of the valve margin is irregularly pitted (Fig.

Redescription. Ontogeny, and Demography of Pciniscolhorax s\mii>o)i(>iJes

Figure 7. Normal naupliar development of Califomian Paiascothora.x synagogoides. based in part on reared larvae, a-e, "nauplii"; a, ventral view; b.
lateral view; c. antennule; d, two antennae; e, two mandibles (setae cut short in d and e); f-g. "early metanauplii." lateral and dorsal views; h-n. "late
metanauplii"; h. dorsal view; i, anterior view with selected limbs shown (redrawn from Grygier, 1987a); j, ventral view showing developing appendages of
ascothoracid larva; k. antennule; I. antenna; m, mandible (setae cut short in I and m); n, ventral and caudal armament. Arrows in c and k mark site of newly
formed seta; many setae omitted in a. b. f. and j. ad. adductor muscle; an. antennule; at. antenna; d. mandible; ff. frontal filament; fl. furcal lobe; la. labrum;
mxl. maxillary rudiments: n. endopod; th. developing thoracopods; tsp. thoracic spines; x, exopod; y, yolk. Scale bars 0.1 mm.

9b). Culicular ctenae line the posterior end internally. No gonads
are present within the carapace. The retracted body occupies no
more than two-thirds of the space between the valves (Fig. 9a). It
has a head, a six-segmented thorax with natatory thoracopods, and a
five-segmented abdomen with a furca.

Cephalic appemkijics. — The antennules are five-segmented, all
the segments being roughly equal (Fig. 9c). The third segment has
tufts of fine hairs anteriorly. The fourth segment has a chin relatively
longer than the adult's, with two distal teeth (lateral one larger), two
unequal soft and vestigial setae on the proximal side, and one (two?)
seta on the distal side. The fifth segment forms a subchela with the
fourth, and it bears a claw with three basal setae, a claw guard with
two short and one minute distal setae, a long seta behind the claw
guard, and a posterobasal strap-like aesthetasc about as long as the
antennule. There is a pair of frontal filament cimiplexes as in the first

ascothoracid larva (Fig. 9d) but no antennae. The conical labrum
surrounds a pair of distally attenuated mandibles and the long, har-
poon-like maxillae. The mandibles are probably unarmed distally,
and the maxillules were not visible in whole mounts.

Thorax and thoracopods. — The thorax is somewhat arched, and
its segments become a little longer and lower posteriorly. The sixth
segment has small lateral epaulets and a dorsal band of fine setae.
The first thoracopods are small and uniramous, with one or two
distal setae (Fig. 9e). Thoracopods 2-5 each have a distinct and
oblong coxa and basis, a laterodistal coxal seta and mediodistal
basal setae on thoracopods 2-4 only, a two-segmented exopod with
four distal setae on the rather narrow second segment, and a three-
segmented endopod with one seta on the second segment and three
on the very narrow distal segment (Fig. 9f). The sixth thoracopod is
much the same except for a "precoxa" and a two-segmented

12

Mark J. Grygier

Figure 8. First-inslar ascolhoracid larva of Califomian Parascollwrax synaf>oi;()iJe.<:. based on reared larvae, a, whole larva, side view, from life; b.
carapace, flaltened ventral view; c. body of several-week-old larva, only invaginaled bases of most thoracopodal and furcal setae shown; d, antennulc
(redrawn from Grygier, 1987b); e. ventral view of mouth field and cephalic appendages on newly molted larva; f, antenna; g, mandible; h, maxillae, an,
antennule; at, antenna; eg, claw guard; ch, chin; cl, claw; d, mandible; en, mandibular endite; ff, frontal filament; fr, furcal ramus; la, labrum; ml, maxillule;
mx, maxillae; n, endopod; p, penis rudiment; x, exopod. Scale bars 0.1 mm.

endopod (Fig. 9g); its exopod has three temiinal setae and the
endopod has two. The setae on the thoracopodal rami are long with
long, widely spaced setules; the protopodal setae are plumose when
present.

Abdomen. — The second and fifth abdominal segments are twice
as long as thick, the first and third are shorter and equal to each
other, and the fourth segment is the shortest (Fig. 9a, h). The first
segment has a very poorly developed (lap-like ventral penis rudi-
ment, and the fifth segment is scaly ventrally. The furcal rami are
rectangular, about twice as long as high, and have four distal setae

(three long ones and a much shorter ventral one), a dorsodistal
spine, and 5 medial setae as long as the temiinal ones, four of these
arising more or less basally, the other mediodorsally.

Larval heliavioi: — The eggs and naupliar stages were neutrally
or slightly positively buoyant in life. The nauplii did not actively
swim. The first ascolhoracid larvae were also buoyant at first, but in
culture they eventually sank. When floating, the first-instar
ascolhoracid larvae had the abdomen tucked forward and the cara-
pace valves closed as tightly as possible. They swam on their backs,
with interspersed periods of non-locomotory abdominal

Redescription, Ontogeny, and Demography of Pcirascothorax synagogoijcs

13

Figure 9. Lasl-instar ascothoracid larva of Califomian Parascolhorax synagogoides (male larvae), a, whole larva with right carapace valve removed; b,
pits along anterodorsal edge of valve, dorsal end above; c, antennule, lateral view; d, frontal filament complex (redrawn from Grygier, 1987c); e, thoracopod
1 ; f, thoracopod 4; g, thoracopod 6 (setae cut short in f and g): h, most of abdomen, ad, adductor muscle; an, antennule; eg, claw guard; ch, chin; cl, claw; co,
cardie organs; es, aesthetasc; fr, furcal ramus; n, endopod; oc, oral cone; x. exopod. Scale bars 0. 1 mm.

contractures, during which they sometimes directed the abdomen
forward beneath the body. In swimming they employed tail flicks
(furcal strokes), spreading the rami at the top of the stroke as each
downbeat began. The power stroke of the thoracopods was
metachronal from rear to front and involved all but the reduced first
pair of legs. To the eye the furcal downstroke seemed to be simulta-
neous with the thoracopods' unified recovery stroke, but efforts to
confirm this cimematographically were unsuccessful. The stroke
rate was over 2 per second, and over 3 per second in one individual,
but their swimming efforts were rather ineffectual because of the

shortness of the thoracopodal setae.

Remarks. — Grygier ( 1987b) divided ascothoracidan nauplii into
those with complex protopodal armament of the antennae and
mandibles and well-developed natatory rami, those with simple
prolopods and well-developed rami, and those with vestigial limbs.
The nauplii of P. syncigogoides belong to the second group, and
those of the various species of Ascothonix belong to the second and
third groups (Grygier, 1983), so the type of nauplius is not useful in
discriminating the two genera. Possession of ai least five naupliar
instars is a plesiomorphy. at least relative to the two naupliar instars

14

Mark J. Grygier

Figure 10. Cysts formed by Califomian Parascothorax sxnagoi'oides on Ophiophlluilmus normani. gemla\ bars of host out of view alongside basal arm
ossicles just within bursal slits, a. incipient cyst forming around newly settled female parasite; b, completed cyst; c. older, perforated cyst. Scale bars 1 mm.

of another ascothoracidan in the same order, Ulophysema
oeresundense (see Brattstrom. 1948); the greatest number accu-
rately known in the Ascothoracida is six, the basic maxillopodan
number, for a species of Baccalaiireus ( ltd and Grygier, 1990) in the
other order, Laurida.

Two instars of ascothoracid larvae, the first being incompletely
formed, occur in other members of the order Dendrogastrida, the
best documented examples being Ulophysema oeresundense and
Ascolhorax gi^as (Brattstrom, 1948; Grygier and Fratt. 1984). 1
have taken this as evidence of a more anamorphic and thus more
primitive ontogeny in the Ascothoracida than in the Cirripedia,
where there is a single cyprid larval instar (Grygier, 1987c). How-
ever, laboratory rearing did not reveal more than one instar of the
ascothoracid larva in the aforementioned species of Baccakntreiis
(Ito and Grygier, 1990), so the more gradual development may
actually be restricted to the Dendrogastrida, or to part of it.

I have previously (Grygier, 1987b) addressed the significance
of the naupliar and ascothoracid larval antennules in the compara-

tive morphology and systematics of the Ascothoracida.
Parascolhorax sxnagogoides rather clearly shows how the claw
arises subterminally in ontogeny and that the more distal part of the
naupliar antennule moves to the posterior side of the appendage and
gives rise to the various sensory elements there (claw guard,
proximal sensory complex). The small lube on the antennular claw
guard in the first-instar ascothoracid larva may be homologous to a
similar tube-like structure seen apically on the aforementioned
ascothoracid larva of Baccalaiireus (Ito and Grygier, 1990), where
it is surrounded by an "apical hood."

There is a progressive reduction in the first-instar ascothoracid
larva of the vestigial rami of the naupliar antennae and mandibles,
and an appearance de novo of a large protopodal spine on the
mandible. This shows that the basal part of the mandible in adult
Parascothorax and other ascothoracidans represents part of the
protopod and that the usually elongate, more or less complexly
armed distal part of the mandible is an endite or gnathobase.

3 4 5 6 7 8

Disc Radius Cmm]

5-1

E1668 /

. •

4-

3-

y=x/ '1 • ■
/ T .-I • : •

•

2-

1-

1 ". t .

3 4 5 6 7

Disc Radius [mmJ

b-

R7145

/ .

,

4-

y=

x/

•

• :

3-

A

•

• •

2-
1-

' — 1 — - — 1 —

1

• •

._ ...

•
1 1

2 3 4 5 6

Disc Radius Cmm]

Figure 11. Relationship in three samples between host disc radius and cyst diameter in Ophicpluluilmiis iiDimani infested with Paniscnthorax
synagogoides off California. Cysts grow to a diameter just under the host disc radius. Large dots represent superimposed records.

Redescription, Ontogeny, and Demography of Paniscothorax synajiogoides

15

CYSTS

Cyst cycle. — Wagin (1964, 1976) described a cycle of cyst
formation and rupture in brittle stars infested with P syiuifiOfioides.
On the basis of the Califomian specimens I review the cycle here in
more detail (Fig. 10: also see Grygier, 1988:778).

A settling female establishes itself within the outer end of a
bursal slit. One female post-larva was found thus In situ with cyst
formation not yet begun, and another was found on the outer
surface of an ophiuroid near a slit. The distal part of the genital bar.
a long ossicle bordering the anibulacral side of the bursal slit (not
visible in Fig. 10), proliferates to cover the end of the slit and also to
thicken the aboral surface above the parasite. The female, most
often still a post-larva, is not yet walled in on the side facing the
interior of the bursa (Fig. lOa).

Later the cyst closes when the proliferating genital bar fuses
with the opposite wall of the bursa. The incorporated bursal wall
does not become as thick as the rest of the cyst and remains
composed of very thin skeletal plates. The exposed part of the cyst
has a very thin skin without the small granules that are otherwise
common externally on the host's disc. At this point about half of the
bursal slit is closed and the cyst barely protrudes beyond the edge of
the disc (Fig. lOb).

As the parasite grows, the diameter of the cyst increases to just
less than the host's disc radius (Fig. 1 1 ). The cyst protrudes notice-
ably below and beyond the margins of the host's disc and gives the
impression of a sphere partly embedded in the ophiuroid (Fig. lOc:
also see Grygier, 1988: fig. 7). The aboral part connects with the
nearest radial shield. Interstices develop between the small ossicles
of the exposed portion, and these eventually perforate the half of the
oral face nearest the arm and the exposed outer and aboral faces:
i.e., small holes develop through all the thickened regions but not
through the bursal wall into the body cavity. The cyst is now held to
the genital bar by numerous trabeculae, is anchored to a radial
shield aborally, and has host skin attached in a arc along the
interambulacral side. Most of the bursal slit becomes blocked, but
the innermost end always remains open because the genital bar does
not reach that fan

Such a cyst is fragile and easily broken, whereupon the parasites
and the outer, oral side of the cyst is lost. The remainder heals,
leaving a gaping scar that permanently disfigures the host.

Wagin (1964) believed that Paniscothorax was exploiting a
defense reaction of its host. The ophiuroid supposedly encapsulates
the settled parasite as an irritant and eventually expels it. Encapsu-
lation certainly does occur, but there is no obvious translocation of
the cyst: it simply grows and remains attached to the genital bar
without any activity on the host's part to expel it.

Host relations. — Ophiophthaliims normani has a disc diameter
of 3.5 to 22 mm (Clark, 1911). Califomian specimens infested with
Parascothora.x syiiago^oldes covered much of this range (2.5-8.0
mm radius). Female parasites were generally loose within a cyst,
but males commonly grasped the thin tissue lining the inside of the
cyst with their antennules. The females fit so snugly that males left
indentations in their carapaces. Males were most often found
against or near the host's genital bar but could also be found
elsewhere. Specimens of O. normani infested with Parascothorax
often have well-developed gonads.

DEMOGRAPHY

Distribution and prevalence. — Of the 15,373 Ophiophthalmiis
mn main <i\dm'mtd at Scripps Institution of Oceanogaphy. 769 were
recorded as being infested with Parascothorax at the time of cap-
ture or having healed scars of old infestations (5.07^ aggregate
infestation). This was an underestimate for reasons explained be-

low. Few samples were entirely free of parasites, and most such
samples were small. The southern Gulf of California (88 ophiu-
roids), the East Cortez Basin (145), the West Cortes Basin (4), a
rather shallow site off La Jolla (896 m: 34 ophiuroids), and an area
off Piedras Blancas Point near Big Sur (252) yielded no
Parascothorax. There was too little comparative material, one or
two samples each, to make much of the incidence in the San Nicolas
Basin (33 of 801 ophiuroids infested), Santa Cruz Basin ( 1 of 73),
an area east of San Clemente Island (14 of 266), and Bahia
Descanso, Baja California (1 of 16). except to say that
Parascothorax does occur there.

I examined a good number of mostly large samples from four
offshore basins, the San Diego Trough (21 samples), the Catalina
Basin (13 samples), the Tanner Basin (7 samples), and the San
Clemente Basin ( 6 samples ) ( Fig. I . Table 1 ). The Tanner Basin had
the most consistent infestation rate, 0.2-1.4% (aggregate 0.5%).
The San Clemente Basin and the Catalina Basin had a much wider
range among samples (0.0-6.2%, aggregate 2.3%, and 0.0-12.1%?,
aggregate 4.5%, respectively), but in the Catalina Basin three of the
samples were much more highly infested (9.4—12.1%) than the
other ten. which together had an aggregate infestation rate of only
0.6%, similar to that in the Tanner Basin. In the San Diego Trough
the prevalence oi Parascothorax varied the most, from 0 to 30%,
and the aggregate incidence was 9.0%, considerably higher than at
any other censused locality and greater than the 1% reported by
Rokop (1975) from the same area (Rokop's samples were included
in my study.).

Additional positive records based on Smithsonian ophiuroids
include USNM 39242 (crustaceans: USNM lAlilX). Albatross sta.
2919, off southern California, south of Cortes Bank, 1799 m, 3 of
18 O. normani infested: USNM ilAA, Albatross sta. 4381, off Los
Coronados Islands near San Diego, 1131-1221 m, 1 of 75 infested;
and USNM 26107, Albatross sta. 4767, Bowers Bank, Bering Sea,
1411 m, 1 of 2 infested. The last is significant because it serves
partly to link the discontinuous known range of P. synagogoldes in
the Sea of Okhotsk and off California. Finally, a sample of O.
normani from the Catalina Basin that I examined at the Allan
Hancock Foundation (AHF 8714.63) included some infested indi-
viduals.

Uiulcrcounts. — The infestation rates mentioned above are often
underestimates because some small cysts were overlooked in the
initial sorting. In detailed resurveys of six samples of sorted, in-
fested ophiuroids, 1.8-13.9% of the cysts actually present had not
been seen and counted the first time. Numerous previously unsus-
pected infestations were found among the supposedly uninfested O.
normani of two samples: for El 668 the initially estimated rate was
14.6% and the revised one was 21.7%^^, and for R7 1 39 the respective
values were 12.4% and 15.2%i. The other heavily infested samples
in Table 1 were probably undercounted by similar margins. On the
other hand, the large sample E2I25, in which only one infested
ophiuroid was found originally, revealed no new finds after half the
sample was reexamined. Therefore, the reported low incidences in
Table 1 are probably trustworthy. The overlooked parasites were
almost all very small, sometimes inhabiting incompletely fomied,
unperforated, non-protruding cysts, and a few had not yet begun to
form a cyst. Their omission does not affect the data on the distri-
bution of males and brooded offspring, both of which are restricted
to larger females, but the missed specimens could have biased the
data on multiple infestations.

Depth distribution. — Parascothorax synagogoides occurred
over almost the whole depth range of its host off southern Califor-
nia ( 1006-1910 m). The well-sampled basins, listed from deepest to
shallowest, are the San Clemente (sampled to 1929 m). Tanner (to
1 397 m ), and Catalina basins (to 1 350 m ) and the San Diego Trough
(to 1 250 m). The aggregate parasite prevalences in the last three are

16

Mark J. Grygier

2

4

5 6

7

0

3

2

0

Figure 12. Geometry of multiple infestations of Ophiophrlwlmiis
normaiii by Parascothorax synagof;oides. a, possible spatial arrangements
of non-superimposed double infestations, cases 2 and 4 being twice as likely
to appear by chance as the others; b, possible spatial arrangements of non-
superimposed triple infestations, all cases equally likely to appear by chance,
with number of observations of each pattern given for pooled samples
E166S, E1439, E1782, and R7145.

progressively higher, but that of the San Clemente Basin is higher
than that of the Tanner Basin, so there is no simple decline in
infestation with depth. In fact, the reverse, an increase with depth, is
evident in the three large samples from the San Clemente Basin
(0.3% at 1 1 14 m, 2.9% at 1535 m, 6.2% at 1830 m). and the three
most heavily infested samples from the Catalina Basin were the
deepest ones. 1275-1350 m versus 875-1250 m for the other
samples). Infestation fates in the San Diego Trough showed no
particular pattern related to depth.

Multiple Infestation

Clumping. — Most often a single bursal opening was afflicted
with Parascothorax, but double or triple infestations were not un-
common. As many as six bursal slits could be involved in rare

cases. This is essentially the same pattern that Wagin (1964) found
in the Okhotsk population. I checked the distribution of the number
of cysts per host against a random (Poisson) distribution by a chi-
square goodness-of-fit test of the data from Table 1 for samples
El 668 and R7139. which were not undercounted. and samples
El 439 and El 762. in which only the initially sorted specimens
were counted. The categories were uninfested. singly infested, and
multiply infested ophiuroids. All these samples differed signifi-
cantly or very significantly from the expected Poisson distribution.
There were too few single infestations and too many uninfested and
multiply infested ophiuroids. I obtained the same results when the
test was repeated without including the empty, broken, and healed
cysts. Therefore. I conclude that Parascothorax has a clumped
distribution among its hosts.

The most obvious explanation for this clumping is that once
infested, an ophiuroid is less resistant to attack by later arrivals.
Because Ophiophthahnus normaiii is an extremely abundant ani-
mal (Smith and Hamilton. 1983). there is no great need to invoke
chemical attraction of female larvae by settled females, as there
might be if the host were rare.

Double infestations.— \n samples El 668. El 439. El 782,
R7139. and R7145 I noted 73 double infestations. Cyst positions
were inadvertently not recorded for three of these, but 1 compared
the other 70 by a chi-square goodness-of-fit test to the expected
random distribution of spatial relationships. If the host is considered
to be purely pentaradial. there are seven distinct ways to place two
cysts so each occupies a distinct bursal slit, and two arrangements
are twice as likely as the others (Fig. 12a). I observed reoccupation
of a previously occupied bursal slit twice, but since the conditions
under which this may occur are different from infestation of a
"virgin" slit, superposition is not included in this analysis. The
observed spatial distribution of double infestations was decidedly
non-random (p < 0.005). and it was clear from inspection that this is
due to a tendency for two cysts to occupy a pair of bursal slits that
lie on opposite sides of the same arm (case 1 in Fig. 12a: 26
occurrences observed versus 7.8 expected). Conversely, finding
both slits of the same interradius occupied (case 7). or slits on the
far sides of adjacent interradii (case 6). was exceedingly uncommon
(2 and 1 occurrences observed, respectively, versus 7.8 expected for
each). The other possible arrangements differed little in actual
occurrence from expectations.

Triple infestations. — There are 12 equally likely distinct ar-
rangements of three cysts without superposition. The samples listed

Table 2. Infestation and population statistics of Parascothorax synagogoides in some samples
of Ophiophthalinus normani"

Sample

Statistic

R7139

El 668

R7128

E1782

R7145

E1439

Number of cysts

70

174

19

107

79

108

Inhabited

55 (79)

153(88)

15(79)

89(83)

73 (92)

66(61)

With feinales

54-55

152-153

15

85-87

72-73

65

With lone males

0-1

0-1

0

2-4

0-1

1

Empty or healed

15(21)

21 (12)

4(21)

18(17)

6(81

42 (39)

Number of brooding t

emales

32 (59)

22(14)

7(47)

28 (33)

20(28)

26 (40)

Without mates

1(3)

1(5)

0(0)

1(4)

1 (5)
17-98"

10(38)

Brood size

4-160

1.3-129

13-183

3-114

3^8

Mean

73.1

52.5

77.7

53.6

54.5

21.1

Standard error

14.7

13.4

38.1

12,2

14.0

4.8

Number of females w

th last-instar

ascothoracid larvae

1(2)

8(5)

0 (0)

5(6)

5(7)

9(14)

Number of females with isopods

3(6)

6(4)

1 (7)

5(6)

3(4)

1 (2)

Percentages in parentheses.

One isopod-infested female had one egg.

Redescription. Ontogeny, and Demography of Parascothoro-X synagogoitles

17

150

120

^90

C/5

"O

o
o

CD
60

30

••

•••

. •

1 ' 1 '

2 3

Carapace Width (mm3

Figure 13. Relation of brood size to female carapace width for five
pooled samples of Califomian Parascothora.\ synagogoides ( R7 1 39, E 1 668.
R7145, E1782. E1439). Large dots represent duplicate records.

above, together with R7128. contained 14 triple infestations. Five
possible distributions did not occur, two appeared three times each,
and three appeared twice (Fig. 12b). There are no obvious charac-
teristics distinguishing the preferred from the unutilized configura-
tions. Curiously, there is no excess of cases with two of the three
cysts opposite the same arm. as would be expected from the pattern
in double infestations. By chance, one-third of the ophiuroids
should show this configuration, and in fact just five of 14 do. Also,
the two configurations that are rare in double infestations occur
often in triple infestations.

There are too few instances of quadruple or higher infestations
to permit a similar analysis.

Population struclwe. — In various samples, from 8 to 39% of
the cysts examined were old, broken, partly healed, or empty of
parasites (Table 2 ). The vast majority of inhabited cysts had a single
female, never more, and zero to five males and/or last-instar
ascothoracid larvae (not more than three of the latter). Depending
on the sample. 14—59% of the females were brooding eggs or
nauplii within their carapaces (Table 2; the probable undercount of
small females in some samples could lower these percentages). The
number of offspring varied enormously, from 3 to 183. largely
depending on the size of the female (Fig. 13). The mean brood size
for those with eggs or larvae was 52-55 in three samples. 73-78 in
two others, and 21 in a sixth, all with large ranges (Table 2). Broods
were always synchronous in development except for a small num-
ber of aborted, perhaps unfertilized eggs in many broods of nauplii.

Not more than six to eight of the 46 1 inhabited cysts contained
just a male Parascolhora.x (Table 2). Such occurrences may have

been due to cysts being broken before examination so the female
could have fallen out, or to severely damaged young females being
mistaken for males. It was unusual for a brooding female to lack an
accompanying male (Table 2). Most such instances were rare
enough to be attributable to observer error, and the carapace of one
supposedly lone female was dented as though a male had been
present but not found. However, I found fully 10 of the 26 brooding
females in sample El 439 to be unaccompanied. Six of these were
brooding undeveloped, presumably infertile eggs, but the other four
had metanauplii, implying that a male had once been present. The
seminal receptacles of these 10 females were not examined, since
they were pooled with the other females after the brood had been
counted.

Maturation and mating. — Figures 14 and 15 are size-frequency
histograms for females of Parascothorax in five samples with
respect to their cyst companions and reproductive state, respec-
tively. With the exceptions of samples El 668 and R7139, where
there was no undercount, the lower ranges of the histograms are
probably incomplete. Most if not all of the overlooked females
would have been immatures without mates (black squares). Despite
this source of error, there does seem to be a much higher proportion
of immature females in sample El 668 than in sample R7I39,
collected just 6 weeks later; both samples were from the San Diego
Trough, though not from precisely the same spot. The difference
could be due to patchy recruitment, differential mortality of newly
invaded ophiuroids, or high mortality of newly recruited
Parascothorax. The later sample did have a higher proportion of
empty and healed cysts (21% versus 12%; Table 2), but I don"t think
these can usually be attributed to the loss of small parasites.

The threshold size for females of Parascothorax to begin ac-
quiring mates is less than that for female maturity, and the size at
which all females have mates is less than that at which all are
brooding (Figs. 14, 15). Immature females, those without develop-
ing oocytes in the ovary diverticula, range roughly from 0.4 to 1 .9
mm in carapace width. Except in sample El 439, which, as noted
above, had an unusually high rate of unaccompanied brooding
females, it was unusual for females larger than about 1.3 mm to be
alone in their cysts. Some down to 1.0 mm or even smaller had
males or last-instar ascothoracid larvae with them. Oocytes begin to
appear between 1 .5 and 1 .9 mm, and broods begin to appear almost
immediately thereafter By 2.6 mm, almost all females are brooding
except for a few spent ones or those infested by isopods.

Since males are immotile, they must join a female as a swim-
ming ascothoracid larva. Such newly arrived larvae, usually in the
process of molting to the male post-larva, are common in cysts.
They usually occur alone with a female, but sometimes also with
other ascothoracid larvae or males (Table 2). Two lines of evidence
suggest that most of these larvae arrive before the cyst fully closes
and temporarily cuts off access to the female. If females accrue
additional mates throughout their lives and there is no significant
male mortality, then larger females should have more males. Table 3
shows the mean sizes of females with different numbers of mates in

Table 3. Mean carapace widths (mm) of mated female Parasco-
thorax with different numbers of mates (males and last-instar
ascothoracid larvae).

Mate

-)

Mates
Mean

3 Mates

5 Mates

Mean

Mean

Mean

Sample

n

Width

n

Width

It

Width

II Width

El 668

59

1.90

16

1.94

5

1..56

—

E1782

47

2.07

12

2.32

5

2,75

2 2.84

R7139

37

2.91

5

2.22

—

—

R714.S

40

1.86

8

2.58

4

1.90

—

18

Mark J. Grveier

Carapace Width (mm]

Carapace Width Cmm]

jL

L

zT

^

p^

■fc-^^i

'^^

z

2 3 4

E1782 Carapace Widlh [mm]

F^l y^^ ^

R7139 Carapace Width (mm)

1 2 3

E1782 Carapace Width (mm)

5

b

s-'i a

2 3

R7139 Carapace Width (mm)

JsopodT

iate metanauplius w^

early metanaupilus^ o

naupliusi;-

embryo r^^

egglj

ovaryi] ^

fi'i^s Carapace Width (mm)

Carapace Width (mm)

Carapace Width (mm)

^'■•sgcarapace Width (mm)

Figure 14. Size-frequency histograms of female carapace width in five
san\p\es of Parascorhorax synagogoides. E1439 is from the Catalina Basin;
the others are from the San Diego Trough. Each female is represented by
one square, and the pattern within the square signifies the number of mates
(0-5 males and/or last-instar ascothoracid larvae) accompanying that fe-
male, according to the key on the right. Each dot above a size-class column
represents a female in that column with one or more ascothoracid larvae as
partners. There was no undercount in El 668 and R7139. collected 6 weeks
apart, but some females at the small end of the size range were probably
missed in the other samples.

Figure 15. Size-frequency histograms of female carapace width for the
same five samples of Parascotlwrax synagogoides as in Fig. 14. Each
female is represented by one square, and the pattern within the square
signifies that female's state of sexual maturity, brood composition, and
presence or absence of hyperparasitic cryptoniscid isopods. according to the
key on the right. Explanation of key: -.no gonads; ovary, gonads evident but
no brood; egg to late metanauplius. five successive stages of brooded
young; isopod. either cryptoniscus stage or adult female isopod present, and
this symbol is sometimes superimposed on the other patterns.

five samples, and only one sample shows the expected patiem.
Additional evidence comes from the distribution of ascothoracid
lai^ae among females of different sizes (Fig. 14). Of 28 females
accompanied by these larvae, most were quite small (24 under 2
mm carapace width, 19 under 1.5 mm), suggesting that most of the
larvae join the females before the cysts close. The few found with
large females probably entered the cysts later, through the second-
ary perforations in the cyst wall.

Number of broods. — Wagin ( 1964) thought that each fetnale of
Parascothorax syna^iogoides produces a single synchronously de-
veloping brood that is released when the cyst breaks open. Eggs and
larvae do escape readily from living females removed from their
cysts, so in nature some broods may be lost from prematurely
broken cysts. But this model poses some problems. The size and
fecundity ranges of brooding females are very broad. For some
females to have only four young and others over 180 in their only
brood is difficult to rationalize. Also, ovaries with oocytes are still
well developed in brooding individuals, and there is apparently no
terminal molt in females; surely a brood must be released before a

molt. 1 think it somewhat likely that P. synagogoides has more than
one successive brood. The length of time a brood takes to develop
and reproductive seasonality cannot be ascertained with present
information.

Hyperparasilism. — In the six samples studied in detail, the
percent infestation of female Parascothorax by an undescribed
cryptoniscid isopod was 1.5-15.4% (aggregate 43%: Table 2). In
E 1 668 and R7 1 39. where Parascollwrax was not undercounted, the
rates were about 6%. Eight of 19 cases involved only a cryptoniscus
(larva or rnale); the others involved a cryptoniscus and a female (6
ca.ses) or a lone female (5 cases). Cryptonisci could he found within
the host's brood chamber or outside of it but still within the ophiu-
roid cyst. Female isopods usually lived within the carapace, filling
the brood chamber, but one was found outside the host within the
cyst. Male Parascothorax accompanied all but one of the infested
females, but males never had attached isopods. In multiply infested
ophiuroids, 1 never found isopods in more than one cyst. Figure 15
shows that isopods occurred mostly with larger female
Parascothorax that would nomially have ripe gonads or be brood-

*

Redescriplion, Ontogeny, and Demography of Parascothorax syiiagogoides

19

ing. The presence of a cryptoniscus apparently does not greatly
inhibit the host's reproductive capacity, aUhough some eggs are
probably lost to the parasite. Of the female isopods, only one very
small one was sharing a brood chamber with host eggs; large female
isopods completely prevent the host's brood deposition and are
therefore parasitic castrators.

Comparison to Other Crustacean Parasites of Ophiuroid Bursae

The demography of two other ophiuroid-associated species of
Ascothoracida and one endoparasitic copepod, A.scoiliorax
ophiocicius. A. i;i,vcis. and Punuhoidcumium (= Amphinrophilus)
amphiwac (Herouard), has been investigated in sufficient detail for
comparison with that oi Parascothorax synagogoides.

Ascothorax ophiocienis. — This is a bursal parasite of shallow-
water Arctic and North Atlantic hosts. Ophiocten sericcum (Forbes)
and O. gracilis (G. O. Sars). 'Wagin (1947) examined about 60.000
O. sericeum from 32 to 1 7S m collected in August and September at
20 stations in the Kara Sea; because infestations were detected by
swellings of the host disc and sorting was done hastily, he thought
that many infested specimens, especially ones with juvenile para-
sites, must have been missed. At 16 stations from which over 100
ophiuroids each were examined, the observed infestation rate
ranged from 0.02 to 2.05% with an aggregate rate of 0.22%, con-
siderably less than the infestation rate of Parascothorax off Cali-
fornia except in the Tanner Basin (0.5%). Ordinarily each infected
bursa (double and triple infestations were observed but not enumer-
ated) contained one adult female and one to four males; no detailed
data on the distribution of the latter was given. Very rarely males
were absent, although the condition of the female's brood under this
circumstance was not stated, and in one case a single bursa had two
adult females and a male, a situation never encountered in
Parascothorax. In cases of multiple infestation, it was normal for
parasites in different bursae to be of different ages, as with
Parascothorax (Fig. 10). Unlike P. synagogoides, A. ophioctenis
ordinarily causes complete castration of the host ophiuroid.

Ascothorax gigas. — Grygier and Fratt (1984) reported on the
infestation of Ophinnoiiis victoriae Bell by A. gigas at 49 to 272 m
around the South Sandwich Islands and Antarctic Peninsula. The
parasites inhabit bursae without developing a cyst, and the infesta-
tion is generally not detectable externally. At four stations in the
South Sandwich Islands, 0-10.5%- of 20 to 355 ophiuroids were
infested; at six stations along the Antarctic Peninsula. 0-20.6%> of
109 to 437 ophiuroids were infested. At two of the latter stations.
the number of parasites per host ranged from 1 to 29 (mean of 7);
muhiple infestations were common, up to seven bursae with up to
seven parasites each being infested. Unlike P. synagogoides and A.
ophiocienis, A. gigas could fit up to three brooding females or a
mixture of brooding and immature females in the same bursa; a few
cases of brooding females without accompanying males were noted.
as in P. synagogoides. The effect of even heavy infestation on the
host was reduced gonad development, not castration.

Parachorcleumiiim amphiurae. — In a recent ecological study of
this copepod living in the bursae of British intertidal Amphiiira
sqiiamata Delle Chiaje (Emson el al.. 1988; Whitfield and Emson.
1988). over 5000 ophiuroids were examined over 13 months. The
copepod occurred with a seasonally varying prevalence ot 10 to
30% (highest in summer), w ith up to five female copepods per host.
The distribution of copepods over potential hosts was clumped, as
in Parascothorax. The smallest ophiuroids were uninfested, and the
prevalence and incidence of infestation increased with host size
except for a reduction in the largest ophiuroids. The reproduction of
infested hosts was delayed and reduced or in cases of multiple
infestations prevented.

Conclusions. — It is clear that not all crustacean bursal parasites

of ophiuroids infest their hosts at the same rate and have the same
physiological effect on them. In most, however, multiple infesta-
tions may be more commonplace than chance would predict. In
part, different variables were measured in the different studies,
limiting their comparability. In the future, standardized information
about such host-parasite systems would be useful.

The present data on Parascothorax represent a rare example of
a detailed ecological study of a parasite (and its hyperparasite) that
afflicts a community-dominating deep-sea invertebrate. Such stud-
ies are so uncommon that no review of invertebrate parasitism in
the deep sea has ever been published. My study was made possible
by the availability of extensive collections from the region, so many
specimens could be spared for parasitological examination. 1 hope
that other large collections of deep-sea invertebrates, perhaps de-
rived from environmental surveys, can be made available to para-
sitologists.

ACKNOWLEDGMENTS

Most of this work formed part of a Ph.D. Dissertation submitted
to the University of California San Diego. I thank Dr W. A.
Newman and Mr S. R. Luke, curator and collections manager,
respectively, of the SIO Benthic Invertebrate Collection, for grant-
ing me access to specimens. Dr K. L. Smith and Ms. N. Brown for
providing additional samples of the host ophiuroid. Dr Newman
for laboratory facilities, and him and Drs. R. R. Hessler. N. D.
Holland. W. H. Berger. and D. S. Woodruff for comments on my
dissertation. 1 thank P. Unit! and two anonymous referees for help-
ing me streamline the manuscript. Mss. M. Downey and C. Aheam
assisted me at the Smithsonian Institution. I thank Drs. Ya. I.
Starobogatov, I. S. Smimov. N. V. Vyshkvartseva, and Ye. L.
Markhaseva (Zoological Institute. USSR Academy of Sciences)
and Dr. T. A. Ginetinskaya (Leningrad State University) for their
cooperation during my stay in Leningrad under the auspices of the
National Academy of Sciences Soviet and East European Exchange
Program. The published manuscript was prepared during a term as a
Visiting Foreign Researcher at the Sesoko Marine Science Center,
University of the Ryukyus, and is a Contribution of Scripps Institu-
tion of Oceanography, new series.

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