Life Sciences Contribution Qf^
Royal Ontario IVIuseum 0>J
A Review of the
Water Mite Genus
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LIFE SCIENCES CONTRIBUTIONS
ROYAL ONTARIO MUSEUM
IAN M. SMITH A Review of the
Water Mite Genus
Publication date: 18 December 1972
Suggested citation: Life Sci. Contr., R. Ont. Mus.
ROYAL ONTARIO MUSEUM
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LIFE SCIENCES EDITORIAL BOARD, 1972-1973
E. J. CROSSMAN
IAN M. SMITH is a doctoral candidate in the Department of Zoology,
University of Toronto. This publication is the result of research carried
out in the Department of Entomology and Invertebrate Zoology, Royal
©The Royal Ontario Museum, 1972
100 Queen's Park, Toronto, Canada
printed at the university of TORONTO PRESS
A Review of the Water Mite
(Acari: Parasitengona: Pionidae)
Males of the genus Nautarachna are recognized for the first
time by association with females of two new species described
from streams in Ontario; A^. muskoka from near Baysville
and A^. queticoensis from near Quetico Provincial Park. The
genus Nautarachna, heretofore the only genus in the family
Nautarachnidae, is placed in the family Pionidae, subfamily
Pioninae, on the basis of characteristic modifications of
iii-L-6 and iv-L-4 in males. A new diagnosis and description
are proposed for the genus Nautarachna and new synonymy
is established. Two polythetic species groups, the muskoka
group and the queticoensis group, are distinguished and the
status of new specimens from western North America is
The systematic status of the genus Nautarachna Moniez, 1888 has here-
tofore been uncertain. Most recently the genus has been considered the
only representative of the family Nautarachnidae (Viets, 1936, 1956;
Cook, 1960). Descriptions of the five species previously included in Nau-
tarachna are inadequate, based on only a few female and nymphal speci-
mens. Males have until now not been recognized, resulting in uncertainty
stated by Cook (1960, p. 227) : "The Nautarachnidae have been tentatively
placed next to the Pionidae but the closeness of this relationship can only
be determined when the type of male sexual dimorphism, if any, is known."
The type of sexual dimorphism present in Nautarachna species is now
known through the association of males and females of two previously
undescribed species from Ontario. This sexual dimorphism is characteristic
for the pionid subfamily Pioninae. Moreover, allocation of Nautarachna
species to the Pioninae is supported by the morphological similarity of
males and females to those of the genus Fiona.
Materials and Methods
In the following descriptions measurements are expressed in microns in the
form: mean of six individuals (minimum value-maximum value). For the
male of Nautarachna muskoka n. sp., only two individuals were measured.
Lengths are measured parallel to, and widths perpendicular to, the long
axis of the body or appendage except in the case of the width of coxae
I + II which is measured perpendicular to the suture between the coxae. The
following conventions have also been adopted:
i) width of coxae i + ii was measured at the level of coxoglandularium i.
ii) length of acetabular plate was measured at the level of coxoglandu-
iii) width of coxa iv was measured from the medial edge of the coxa to the
outer edge of the insertion of leg iv.
iv) width of dorsal shield was measured at the level of lateroglandularium
The abbreviations used for the segments of the appendages are given by
Family Pionidae Thor 1900
Nautarachnidae Viets, 1935, p. 664. new synonymy.
Subfamily Pioninae Wolcott 1905
Nautarachninae Walter, 1925, p. 45. new synonymy.
Pionellinae Viets, 1937, p. 295. new synonymy.
Genus Nautarachna Moniez 1888
Pionella Viets, 1937, pp. 294-298. new synonymy.
See notes under N. karamani.
Fiona Walter, In Bader, 1955, pp. 65-67. new synonymy.
See notes under N. scutata.
Integument with extensive dorsal and ventral sclerotized shields in male,
membranous or with extensive dorsal and ventral sclerotized shields in
female; P-iv with one large, ventromedial, distally-directed, curved, seti-
t'erous tubercle in male; anterior end of coxa i bearing 2-4 heavy setae in
male, 3-4 heavy setae in female; posteromedial edge of coxa iv broadly
rounded in female; swimming hairs relatively few when compared with
Male: Body round, slightly flattened dorsoventrally.
Dorsum (Figs, lb, 3b) : Nearly covered by a single, large, sclerotized
dorsal shield, oval and centrally located, that bears all pairs of dorsoglandu-
laria and some pairs of lateroglandularia; separated laterally and posteriorly
from ventral shield by narrow strip of unsclerotized integument, anteriorly
either separated from or continuous with ventral shield between eyes.
Venter (Figs, la, 3a): All structures incorporated into a single, large,
sclerotized ventral shield, rounded and extending dorsally up anterior,
lateral and posterior surfaces of body. Coxae arranged in four groups as in
Fiona but with edges more or less obliterated by fusion with ventral shield.
Coxae I with medial edges widely separated anteriorly, converging to near
midlength, posterior halves fused with ventral shield, sutures obliterated
medially, poorly defined posteromedially; each coxa i bearing 2-4 heavy
setae anteriorly and three fine setae, two near medial edge in anterior half,
the third posteromedially. Suture between coxa i and coxa ii distinct. Coxa
II marginally augmented posteriorly by extensive sclerotization of adjacent
integument, including coxoglandularium i, fused with anterior edge of coxa
III, suture distinct to a point immediately lateral to posteromedial edge of
coxa i; bearing three setae in anterolateral half. Coxae in fused medially,
suture partial and poorly defined; each coxa in bearing four fine setae, three
in anterolateral half, one medially. Suture between coxa iii and coxa iv dis-
tinct except medially. Coxae iv fused medially, suture poorly defined; each
coxa IV with posterior edge transversely concave, broadly angulate postero-
laterally, weakly convex to straight laterally; posterior and lateral edges
fused with ventral shield, sutures poorly defined or obliterated; bearing 3-5
fine setae near edge of insertion of leg iv, one fine seta posteromedially.
Gonopore embedded in ventral shield, flanked on either side anteriorly by
a group of four or five small setae, posteriorly by a group of 3-5 small setae.
Acetabular plates elongate, wing-like, embedded in ventral shield; each
plate extending laterally from near edge of gonopore to point just beyond
level of insertion of leg iv; each bearing numerous acetabula. Coxoglandu-
larium ii embedded in ventral shield between acetabular plate and midpoint
of posterior edge of coxa iv. Excretory pore and all ventroglandularia em-
bedded in ventral shield, anteriormost pair of ventroglandularia borne on
small, conical projections ventromedial to eyes.
Appendages: Capitulum partially protrusible on membranous tube of
integument; P-iv (Figs. Ic, 3c) markedly modified, bearing one large,
distally-directed, curved, tubercle arising near midpoint of ventromedial
surface, extending nearly to end of segment, bearing two fine setae. Legs
with relatively few swimming hairs; sexually dimorphic as in Fiona; iii-L-6
(Figs. 3d, 5a, 5d) blunt, club-shaped, bearing terminally one stout, straight
spur and one large, curved claw; iv-L-4 (Figs. 5b, 5c) with deep rounded,
posterodorsal concavity bearing numerous peg-like setae.
Female: Body ovoid to round, either strongly arched or slightly flattened
Dorsum (Figs. 2b, 4b): Membranous, as in Fiona, bearing one pair
small dorsalia, or with single, large, central, oval, sclerotized, dorsal shield
separated from ventral shield anteriorly, laterally and posteriorly by narrow
strip of unsclerotized integument.
Venter (Figs. 2a, 4a): Membranous, as in Fiona, or with a single, large,
sclerotized, ventral shield, rounded and extending dorsally up anterior and
lateral surfaces of body. Coxae arranged in four groups as in Fiona but with
edges marginally augmented by sclerotization of adjacent integument and
more or less obliterated by fusion with ventral shield when present. Coxae i
with medial edges widely separated anteriorly, converging to near mid-
length, continuing parallel to one another for posterior half, either separated
by a strip of integument or fused with ventral shield; each coxa i bearing
three or four heavy setae at anterior end and three fine setae, two near
medial edge in anterior half, the third posteromedially. Coxa ii marginally
augmented medially and posteriorly by sclerotization of adjacent integu-
ment; bearing three or four setae in anterolateral half; separated from coxa
III by a narrow strip of integument bearing coxoglandularium i, or fused
with anterior edge of coxa iii and including coxoglandularium i. Coxa iii
marginally augmented medially, anteriorly and laterally by sclerotization
of adjacent integument that continues as marginal extension of coxa iv
medially, posteriorly and laterally; fused medially with ventral shield when
present; bearing one heavy and two or three fine setae in anterolateral half
and one fine seta medially. Coxa iv broadly rounded posteromedially,
obtusely angled posteriorly, convex laterally; bearing three or four fine
setae near edges of insertion of leg iv and one or two fine setae postero-
medially. Gonopore borne in integument between coxae iii and iv with
distinct pregenital and postgenital sclerites, or embedded in ventral shield
with sclerites obliterated; flanked bilaterally by two or three setae. Ace-
tabular plates wing-like, borne in integument or embedded in ventral shield;
each plate extending laterally from near edge of gonopore to a point pos-
terior to or beyond level of insertion of leg iv; bearing numerous acetabula;
with 2-4 small setae on or immediately medial to plate. Coxoglandularium
II borne on small, weakly sclerotized plate in integument, or embedded in
ventral shield, between acetabular plate and midpoint of posterior edge of
coxa IV. Excretory pore and ventroglandularia borne on small, weakly-
sclerotized plates in integument or embedded in ventral shield.
Appendages: Capitulum partially protrusible on membranous tube of
integument. P-iv (Figs. 2c, 4c) without setiferous tubercle. Legs (Figs. 2d,
4d) as in Fiona but with fewer swimming hairs.
SPECIES OF THE GENUS NAUTARACHNA
Nautarachna asperrima Moniez
N autarachna asperrimum Monitz, 1888, pp. 64-68.
Nautarachna asperrima Moniez. Walter, 1925, pp. 46-49, pi. 2, figs. 30-33.
This species, the generotype, was described from a nymphal specimen taken
in the littoral zone of the Atlantic Ocean at Cayeux-sur-Mer, France.
Walter (1925) redescribed A^. asperrima from the type specimen and was
the first to recognize its affinity with the present family Pionidae, establish-
ing the subfamily Nautarachninae for this and the following species. No
definite adult association has been established for A^. asperrima.
Nautarachna crassa (Koenike)
Delmea crassa Koenike, 1908, pp. 704-707.
Nautarachna crassa (Koenike). Walter, 1925, p. 11.
A^. crassa was originally described from a single female specimen taken from
the Delme River at Delmenhorst, Oldenburg, Germany, and assigned to the
new subfamily Delminae (Koenike, 1910). Walter (1925) synonymized
Delmea with Nautarachna on the basis of similarities between the nymph
of N. asperrima and the female of A^. crassa. The description of the nymph
of N. crassa by Viets (1936) confirmed the synonymy. Nautarachna females
have been reported subsequently from several localities in Europe, and
all have been referred to N. crassa despite considerable variation among
the individuals taken (see Koenike, 1908 and Viets, 1936). Males of N.
crassa have not yet been recognized with certainty (but see notes for N.
karamani). Habeeb (1956a, 1956b, 1957) has referred a nymphal speci-
men from New Brunswick, Canada, to N. crassa.
Nautarachna karamani (Viets)
Pionella karamani Viets, 1937, pp. 294-298. new synonymy.
Described from a specimen collected in the Krka River at Ljubljana, Jugo-
slavia, this species is based on a Nautarachna male, probably that of A^.
crassa. Viets (1937) reported an imagochrysalis of N. crassa in the col-
lection containing the type of P. karamani. Halbert (1944) subsequently
reported a male, referred to P. karamani, and a female of Nautarachna
crassa, in River Flesk, Killarney, North Kerry, Eire.
Nautarachna scutata (Walter)
Fiona scutata Walter, In Bader, 1955, pp. 65-67. new synonymy.
From the description and figures it seems that this species is also based
upon a Nautarachna male. Possibly the type specimen formed the basis for
the nomen nudum Nautarachna processijera in Walter's 1925 paper for the
same locality, Vierwaldstattersee, Switzerland, is involved in both cases.
Walter may have had evidence for the association of males and females
of the genus Nautarachna at that time but if so did not publish it. It is pos-
sible that N. scutata is a synonym of N. crassa. A comprehensive compara-
tive study of all European material is necessary to determine that systematic
status of both N. scutata and N. karamani.
Nautarachna neogaea (Habeeb)
Pionella neogaea Habeeb, 1955, pp. 1-3. new synonymy.
This species is known only from the type locality, Fallsbrook, Grand Falls,
Nautarachna karl-vietsi Habeeb
Nautarachna karl-vietsi Habeeb, 1957, pp. 51-52.
This species was described from a single nymph taken in a stream near a
saline spring in New Brunswick, Canada.
Nautarachna pioniformis Cook
Nautarachna pioniformis Cook, 1960, pp. 228-230.
This distinctive species was described from a female specimen taken in a
stream in Wyoming, U.S.A.
Nautarachna calif ornica Cook
Nautarachna calif ornica Cook, 1960, pp. 227-228.
Described from a female specimen from a stream in California, this species
was subsequently reported from Colorado (Young, 1969, p. 388).
Nautarachna muskoka n. sp.
male: Dorsum (Fig. lb): Dorsal shield bearing all pairs of dorsoglandu-
laria and all but the fourth pair of lateroglandularia; continuous with
ventral shield anteriorly between eyes.
Venter (Fig. la): Coxa i bearing three or four heavy setae at anterior
end. Coxa ii with one heavy seta and two fine setae in anterolateral half.
Coxa IV bearing three fine setae posterior to and one fine seta medial to edge
of insertion of leg iv. Gonopore flanked anteriorly by a group of five small
setae on each side. Each acetabular plate with one fine seta posteriorly and
Measurements (in microns): Length of coxa i, 237 (236-238); length
of coxae, 425 (420-429); width of coxae i + ii, 115 (112-117); width of
coxa IV, 210 (206-213) ; width of acetabular plate, 247 (243-250) ; length
of acetabular plate, 49 (47-50); length of gonopore, 48 (45-50); leng;th
of chelicera, 251 (248-253); length of dorsal shield, 547 (545-549);
width of dorsal shield, 420 (410-430); number of acetabula per plate, 40
Dorsal lengths of palp segments: P-i, 35 (32-37); P-ii, 139 (134-144);
P-iii, 62; P-iv, 115 (112-117); P-v, 53 (50-55).
Dorsal lengths of leg segments: i-L-1, 64 (62-65); i-L-2, 78 (74-82);
i-L-3, 86 (84-87); i-L-4, 115 (112-117); i-L-5, 158 (154-161); i-L-6,
182 (179-184). ii-L-1, 74; ii-L-2, 85 (82-87); ii-L-3, 90 (87-92);
ii-L-4, 135 (134-136); ii-L-5, 177 (174-179); ii-L-6, 195 (191-198).
iii-L-1, 78 (77-79); iii-L-2, 86 (82-89); iii-L-3, 91 (89-92); iii-L-4,
155 (154-156); iii-L-5, 219 (216-221); iii-L-6, 130 (126-134). iv-L-1,
156; iv-L-2, 116 (114-117); iv-L-3, 88 (84-92); iv-L-4, — ; iv-L-5, 187
(186-188); iv-L-6, 183 (181-184).
Arrangement of swimming hairs: i-L-4, 0; i-L-5, 0. ii-L-4, 2; ii-L-5, 6.
iii-L-4, 0; iii-L-5, 9. iv-L-4, 2; iv-L-5, 9.
female: Dorsum (Fig. 2b): Membranous; strongly arched; bearing one
pair of small dorsalia; with dorso- and lateroglandularia borne on small,
paired, weakly sclerotized plates in integument.
Venter (Fig. 2a) : Integument membranous. Coxae i separated in pos-
terior half by strip of integument of width slightly less than that of a coxa i.
Coxa I bearing three or four heavy setae at anterior end. Suture between
coxa I and coxa ii distinct except posteromedially. Coxa ii with two or three
heavy setae and one fine seta in anterolateral half. Coxoglandularium i
situated in narrow strip of integument separating coxa ii and coxa in. Coxa
III bearing two fine setae in anterolateral half. Suture between coxa in and
coxa IV obliterated medially. Coxa iv broadly convex laterally; with three
fine setae posteromedial to and one fine seta anteromedial to insertion of
leg IV, one fine seta medially. Gonopore borne in integument, with distinct
pregenital and postgenital sclerites; flanked by three colinear setae on either
side. Pregenital sclerite borne in strip of integument between coxae iii and
IV of width about two and one half times that of pregenital sclerite. Each
acetabular plate borne in integument; extending laterally from near edge
of gonopore to point posterior to insertion of leg iv; bearing 39-75 ace-
tabula and 2-4 fine setae. Coxoglandularium ii, excretory pore and all
ventroglandularia borne in integument.
Measurements'. Length of coxa I, 293 (280-315); length of coxae in +
IV, 410 (392-440); width of coxae i + ii, 130 (119-136); width of coxa
IV, 285 (258-315); width of acetabular plate, 306 (280-347); length of
acetabular plate, 101 (87-124); length of gonopore, 245 (211-267);
width of pregenital sclerite, 110 (97-124); width of postgenital sclerite, 76
(67-87); length of chelicera, 320 (300-325); length of dorsalium, 82
(76-89); width of dorsahum, 43 (40-47); number of acetabula per plate,
Dorsal lengths of palp segments: P-i, 37 (35-42); P-ii, 138 (129-151);
P-iii, 69 (62-74); P-iv, 141 (131-154); P-v, 57 (55-62).
Dorsal lengths of leg segments: i-L-1, 82 (77-99); i-L-2, 92 (87-104);
i-L-3, 102 (92-114);i-L-4, 150 (134-164); i-L-5, 182 (176-198); i-L-6,
190 (184-211). ii-L-1, 86 (76-102); ii-L-2, 103 (97-112); ii-L-3, 116
(112-124); ii-L-4, 177 (171-193); ii-L-5, 217 (211-236); ii-L-6, 217
(206-228). iii-L-1, 92 (87-99); iii-L-2, 110 (99-119); iii-L-3, 113
(97-126); iii-L-4, 189 (181-203); iii-L-5, 241 (231-260); iii-L-6, 221
(211-233). iv-L-1, 125 (114-144); iv-L-2, 131 (124-141); iv-L-3,
139 (134-149); iv-L-4, 229 (221-253); iv-L-5, 253 (243-278); iv-L-6,
Arrangements of swimming hairs: i-L-4, 1 or 2; i-L-5, 3 to 5. ii-L-4, 3 or 4;
ii-L-5, 8. iii-L-4, 4; iii-L-5, 9 or 10. iv-L-4, 5; iv-L-5, 9 or 10.
types: Holotype: Male, taken in a small pool near the mouth of the small
creek flowing into northwest side of Echo Lake, Baysville, Muskoka Dis-
trict, Ontario (45°irN, 79°4'W); 21 July 1971.
Paratypes: Two males, same data as holotype; 22 females, same locality
as holotype; 20-25 Jtily 1971. Holotype deposited in the Department of
Entomology and Invertebrate Zoology, Royal Ontario Museum; paratypes
in the Royal Ontario Museum, the Canadian National Collection and the
Chicago Natural History Museum.
habitat: Small pools (maximum width 10 feet, maximum depth 3 feet)
with slow current near the mouth of a small, cool creek flowing through
mixed forest. Substrate is of fine silt with sparse rooted aquatic vegetation.
Most specimens were taken under overhanging banks among roots.
remarks: On the basis of the morphology of the female, this species is
allocated to a species group with N. californica, N. pionijormis and N.
crassa that is characterized by the absence of sclerotized shields in the
membranous integument of both dorsum and venter, and by small size. Afl
known males of this species group have the dorsal and ventral shields con-
tinuous anteriorly between the eyes. The characters previously used to dis-
tinguish species in this group are highly and continuously variable in the
N. muskoka population. Separation of these species is greatly hampered by
lack of knowledge of interspecific variability. For example, Cook (1960),
in separating N. calif ornica from A^. crassa on the basis of Viets (1936, fig.
335), used the number of heavy setae at the anterior end of coxa i, acetabu-
lar number and the shape of the acetabular plates. Not only is the A^. mus-
koka population polymorphic for each of these characters, but the figure
of A^. crassa given by Viets (1936) does not agree with the figure given for
this species in the original description by Koenike (1908, fig. 1) in these
characters. Until more complete descriptions based on several specimens
of each sex are available for all known species of Nautarachna, detailed
remarks on their affinities are not possible.
I have collected males and females of N. muskoka from silty substrate of
a small, cool, slowly flowing creek in Ontario (east side of Highway 11, 3
miles south of Trout Creek, Nipissing District; 14 May 1972, 1 June 1972;
ROM ) . I have taken two females and one male of a species of the muskoka
group in Nevada (Cabin Creek near Hinkey Summit, Paradise Valley,
Humboldt Co.; 31 May 1968; rom). These specimens possess very short,
wide acetabular plates bearing approximately 20 acetabula per side in the
male and 35 acetabula per side in the female. In other characters, these
individuals are similar to specimens of A^. muskoka. They may belong to
A^. californica but this cannot be decided until more western material is
Provisional Key to Females of the muskoka Group
1. Acetabular plates as long as wide (Cook, 1960, fig. 10).
A^. pioniformis Cook
Acetabular plates much wider than long (Fig. 2a) 2
2. Medial edges of acetabular plates extending anteriorly beside gonopore
over half its length (Koenike, 1908, fig. 1; Viets, 1936, fig. 335).
A^. crassa (Koenike)
Medial edges of acetabular plates extending anteriorly beside gonopore
not more than one-third of its length (Fig. 2a) 3
3. Coxae not marginally augmented by sclerotization of adjacent integu-
ment; coxa IV acutely angled posteriorly (Cook, 1960, fig. 1).
^ A^. californica Cook
Coxae marginally augmented by sclerotization of adjacent integument;
coxa IV relatively rounded posteriorly (Fig. 2a) A^. muskoka n. sp.
Nautarachna queticoensis n. sp,
male: Dorsum (Fig. 3b): Dorsal shield bearing all pairs of dorsoglandu-
laria and second pair of lateroglandularia; separated from ventral shield
anteriorly between eyes by narrow strip of membranous integument.
Venter (Fig. 3a) : Coxa i bearing two to four heavy setae at anterior end.
Coxa II with two heavy setae and one fine seta in anterolateral half. Coxa iv
bearing two or three fine setae posterior to, rarely one fine seta postero-
medial to and one or two fine setae anteromedial to insertion of leg iv.
Gonopore flanked anteriorly by a group of four or five small setae on each
side. Each acetabular plate with 58-83 acetabula.
Measurements'. Length of coxa i, 350 (344-360); length of coxae, 622
(611-649); width of coxae i + ii, 172 (159-184); width of coxa iv, 356
(344-372) ; width of acetabular plate, 387 (363-410) ; length of acetabular
plate, 111 (92-124); length of gonopore, 64 (60-67); length of chelicera,
396 (382-420); length of dorsal shield, 880 (831-926); width of dorsal
shield, 724 (649-783); number of acetabula per plate, 72 (58-83).
Dorsal lengths of palp segments: P-i, 55 (50-57); P-ii, 184 (169-188);
P-iii, 83 (74-92) ;P-iv, 166 (159-179); P-v, 47.
Dorsal lengths of leg segments: i-L-1, 118 (99-129); i-L-2, 129 (117-
144); i-L-3, 120 (117-124); i-L-4, 183 (179-186); i-L-5, 248 (246-
250); i-L-6, 230 (226-241). ii-L-1, 119 (112-126); ii-L-2, 132 (129-
136); ii-L-3, 129 (124-136); ii-L-4, 214 (211-218); ii-L-5, 281 (270-
288);ii-L-6, 258 (250-265). iii-L-1, 123 (119-129); iii-L-2, 136 (131-
149);iii-L-3, 130 (124-136); iii-L-4, 239 (233-248); iii-L-5, 311 (305-
322);iii-L-6, 161 (159-174). iv-L-1, 217 (198-228); iv-L-2, 177 (169-
186); iv-L-3, 131 (124-136); iv-L-4, 235 (226-241); iv-L-5, 306 (303-
310);iv-L-6, 299 (283-308).
Arrangement of swimming hairs: i-L-4, 1 ; i-L-5, 2. ii-L-4, 1 ; ii-L-5, 3 to 5.
iii-L-4, 1; iii-L-5, 6. iv-L-4, 2; iv-L-5, 3 or 4.
female: Dorsum (Fig. 4b): Slightly flattened dorsoventrally; nearly
covered by dorsal shield bearing all four pairs dorsoglandularia, and
second pair lateroglandularia; surrounded by strip of membranous integu-
ment bearing other three pairs lateroglandularia.
Venter (Fig. 4a): Most structures incorporated into ventral shield. Pos-
terior half of coxa i fused with ventral shield, suture obliterated medially,
weak posteromedially. Coxa i bearing three or four heavy setae at anterior
end. Suture between coxa i and coxa ii distinct. Coxa ii with one heavy
seta and three fine setae in anterolateral half; fused with anterior edge of
coxa III, including coxoglandularium i. Coxae in fused medially with ventral
shield, sutures distinct, separated by distance less than width of gonopore.
Coxa III bearing three fine setae in anterolateral half. Suture between coxa
III and coxa iv distinct. Coxa iv weakly convex laterally; edges fused with
ventral shield, sutures distinct; with two fine setae posterior to and one fine
seta anteromedial to edge of insertion of leg iv, two fine setae medially.
Gonopore embedded in ventral shield; flanked by two or three setae on
either side. Each acetabular plate embedded in ventral shield; extending
laterally from near midventral line posterior to gonopore to point beyond
level of insertion of leg iv; flanked medially by an arc of three small setae;
bearing 85-110 acetabula. Coxoglandularium ii and ventroglandularia i
and II embedded in ventral shield, ventroglandularia i borne on small,
conical projections ventromedial to eyes. Excretory pore and ventroglandu-
laria III, IV and V situated in membranous integument posterior and lateral
to ventral shield.
Measurements: Length of coxa i, 391 (367-409); length of coxae, 660
(635-669); width of coxae i + ii, 225 (208-248); width of coxa iv, 347
(334-360) ; width of acetabular plate, 485 (461-516) ; length of acetabular
plate, 230 (208-260) ; length of gonopore, 271 (253-285) ; length of cheli-
cera, 419 (401-430); length of dorsal shield, 1117 (1041-1184); width
of dorsal shield, 919 (869-965); number of acetabula per plate, 97 (87-
Dorsal lengths of palp segments: P-i, 57 (52-65); P-ii, 190 (179-203);
P-iii, 92 (82-102); P-iv, 194 (188-211); P-v, 65 (62-69).
i-L-2, 131 (124-
i-L-5, 262 (248-
ii-L-2, 146 (141-
ii-L-5, 297 (278-
iii-L-2, 152 (146-
iii-L-5, 344 (337-
iv-L-2, 183 (176-
iv-L-5, 37'8 (365-
Dorsal lengths of leg segments: i-L-1, 110 (99-119)
144); i-L-3, 136 (129-149); i-L-4, 204 (193-211)
273); i-L-6, 253 (243-263). ii-L-1, 118 (112-128)
159); ii-L-3, 147 (141-156); ii-L-4, 238 (223-248)
308); ii-L-6, 286 (268-303). iii-L-1, 124 (112-129)
161);iii-L-3, 149 (144-161); iii-L-4, 260 (248-270)
360);iii-L-6, 303 (290-320). iv-L-1, 196 (188-201)
201);iv-L-3, 189 (176-201); iv-L-4, 346 (332-357)
389);iv-L-6, 333 (315-350).
Arrangement of swimming hairs: i-L-4, 1; i-L-5, 2. ii-L-4, 1; ii-L-5, 2 to 4.
iii-L-4, 1; iii-L-5, 5 or 6. iv-L-4, 2; iv-L-5, 3 or 4.
types: Holotype: Male taken in a small stream on a hillside on the south
side of Highway 11, 5.1 miles west of the entrance to Dawson Trail Camp-
ground, Quetico Provincial Park, Rainy River District, Ontario (48°40'N,
91°7'W); 10 June 1971.
Paratypes: 11 males, 20 females, same data as holotype. Holotype de-
posited in the Department of Entomology and Invertebrate Zoology, Royal
Ontario Museum; paratypes in the Royal Ontario Museum, the Canadian
National Collection and the Chicago Natural History Museum.
habitat: Small stream (maximum width 2 feet, maximum depth 6 inches)
flowing down a hillside through mixed forest. Substrate varies from fine silt
and rocks in pools to vegetation covered rocks in riffles. Specimens were
taken in both situations.
remarks: This distinctive species is considerably larger and the female
much more heavily sclerotized than those of the muskoka group and seems
to represent a new subgeneric species group. The characters of the male
clearly show its close affinity with the other species of Nautarachna.
I have also collected specimens of A^. queticoensis in vegetation on rocks
in riffle areas of very small streams in Ontario (on south side of Highway
11, 7.2 miles south of Beardmore, Thunder Bay District; 21 June 1971;
ROM; and on east side of Highway 127, 9.7 miles south of junction of High-
way 127 and Highway 60; 10 May 1972; rom) and in Quebec (on north
side of Highway 59, 12.3 miles west of Arntfield; 25 May 1972; rom). Two
female specimens of Nautarachna (rom), taken in British Columbia (pool
in a small stream crossing the Trans-Canada Highway 19.9 miles north
of Golden; 25 July 1969), possess very long acetabular plates bearing
Figs. 1-4 Nautarachna n. spp. (1 scale div. = 25/Lt).
1. N. muskoka n. sp. <J : a) ventral view; b) dorsal sclerites; c) palp, lateral
2. TV. muskoka n. sp. 9 : a) ventral view; b) dorsalia; c) palp, lateral view;
d) leg I.
3. N. queticoensis n. sp. (5 : a) ventral view; b) dorsal sclerites; c) palp,
lateral view; d) leg in.
4. N. queticoensis n. sp. 9 : a) ventral view; b) dorsal sclerites; c) palp,
lateral view; d) leg i.
Nautarachna n. spp. (Scale: 4.8 mm.
N. muskoka n. sp. $ iii-L-5, 6
A'^. muskoka n. sp. $ Leg iv
N. queticoensis n. sp. $ Leg iv
N. queticoensis n. sp. $ Leg in
about 1 50 acetabula each and certainly belong to this species group. Other-
wise, they are similar to N . queticoensis. A decision on the systematic status
of this population should await the collection of more individuals of both
The type of sexual dimorphism exhibited in iii-L-6 and iv-L-4 by species
of Nautarachna indicates their close relationship with species of the genus
Fiona. Since the modifications of these segments exhibited by males of
Nautarachna species are characteristic for the Pioninae, the genus Nauta-
rachna should be placed in this subfamily. Although the genera Nautarachna
and Fiona have many morphological characters in common, it seems that,
on the basis of available material, the genus Nautarachna should be re-
tained for those species of the Pioninae possessing the following character-
istics: males with extensive, sclerotized, dorsal and ventral shields; one
large, ventromedial, distally-directed, setiferous tubercle on P-iv; 2-4 heavy
setae at anterior end of coxa i; number of swimming hairs relatively few.
Females with broadly convex posteromedial edge of coxa iv; no setiferous
tubercle on P-iv; three or four heavy setae at anterior end of coxa i; number
of swimming hairs relatively few.
The species of Nautarachna appear to form two groups based on the
degree of integumentary sclerotization and size. The muskoka group, char-
acterized by anterior connection of dorsal and ventral shields in the male,
absence of large dorsal and ventral shields in the female and relatively small
size, includes A^. muskoka, N. calif ornica, N. pioniformis and N. crassa. The
queticoensis group, characterized by lack of an anterior connection of dorsal
and ventral shields in the male, presence of large dorsal and ventral shields
in the female and relatively large size, contains only N. queticoensis thus
Nautarachna species are local in distribution. This fact, coupled with
considerable intraspecific variation, may result in persistent difficulties in
establishing species diagnoses based on a few characters. (See remarks
under A^. muskoka.) It would seem advisable to determine the variation
that can be expected in a population of Nautarachna before taxonomic deci-
sions are made.
Of the ten described species of Nautarachna, seven have been reported
from cool, lotic habitats, one from a freshwater, alpine lake, one from the
vicinity of a sahne spring and the other from the marine littoral. Walter
(1925) and Sokolow (1936) suggested that the occurrence of N. asperrima
in the ocean was accidental. However, the record from New Brunswick
(Habeeb, 1957) may indicate that the relationship of Nautarachna with
saline habitats warrants further investigation.
The marked sexual dimorphism in the structure of P-iv in the species of
the genus Nautarachna is unusual among water mites and probably con-
tributed to the failure of previous workers to associate the sexes of this
genus. The many morphological similarities and the consistent association
of these males and females in natural habitats provides undoubted evidence
for their congeneric relationship. Further accumulation of material and
revisionary work are required to resolve the remaining species level taxo-
nomic difficulties in this genus.
I acknowledge with gratitude the assistance and encouragement of Drs.
Glenn Wiggins and David Barr of the Department of Entomology and
Invertebrate Zoology, Royal Ontario Museum. Dr. John Kethley of the Chi-
cago Museum of Natural History loaned holotypes of A^. calijornica and
N. pioniformis. Thanks are due to Messrs. Tosh Yamamoto and Henry
Frania for assistance in the collection of specimens, Mr. Anker Odum for
criticism of the line drawings and photographs, and Mrs. Judy Allan for
typing the manuscript.
The research resulting in this publication was done under a National
Research Council Postgraduate Scholarship. This study was supported by
a National Research Council of Canada grant to Dr. G. B. Wiggins (grant
A5707). Some collections were made during rom field trips supported by
the National Science Foundation (grant GB4021), the Canadian National
Sportsmen's Show and the Fisheries Research Board of Canada.
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