VOLUME 103 PART 3 MAY 1993 ISSN (0303-2515

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BuLLouGH, W. S. 1960. Practical invertebrate anatomy. 2nd ed. London: Macmillan.

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FiscHEr, P. H., Duvat, M. & Rarry, A. 1933. Etudes sur les échanges respiratoires des littorines. Archives de zoologie
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THIELE, J. 1910. Mollusca. B. Polyplacophora, Gastropoda marina, Bivalvia. In: SCHULTZE, L. Zoologische und anthro-
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ANNALS OF THE SOUTH AFRICAN MUSEUM
ANNALE VAN DIE SUID-AFRIKAANSE MUSEUM

Volume 103 +#£4Band
May 1993 Mei
Part 3 Deel

A NEW SPECIES OF STREPTOCEPHALUS
(CRUSTACEA, BRANCHIOPODA,
ANOSTRACA) FROM NAMIBIA

By
MICHELLE HAMER
&

LUC BRENDONCK

Cape Town Kaapstad

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D2072

A NEW SPECIES OF STREPTOCEPHALUS
(CRUSTACEA, BRANCHIOPODA, ANOSTRACA)
FROM NAMIBIA

By

! MICHELLE HAMER
Department of Zoology & Entomology, University of Natal, Pietermaritzburg,
South Africa

&

Luc BRENDONCK

Laboratory for Biological Research in Aquatic Pollution, University of Gent,
J. Plateaustraat 22, B 9000 Gent, Belgium

(With 2 figures)

[MS accepted 23 November 1992]

ABSTRACT

The adult male and egg morphology of a new anostracan species, Streptocephalus namibiensis, are
described and illustrated. The new species resembles S. proboscideus and can be allocated to the same
species group which also includes S. trifidus. Streptocephalus namibiensis has been collected from
Bushmanland (northern Namibia), central Namibia, northern Botswana and the Transvaal Highveld
(South Africa).

CONTENTS

PAGE
EN EGO CU CEO Meee ee eee ee eee ee eee teeta re ae 183
MatenralsandimethodSencsecsscnostcoa totic sone. net core eee eee ee mate 184
(axonomicidescriptlone. 2c: :e2.-cesccacuste sms. ce cette e seme ere canes: hese 184
DD ISCHSSIO Tee eae Ne ee AER a octet act mn ARN ORES ee py 188
AX CKHOWICUREMCHIES =: ane 24. tance merceneee cee an se neraberinememcay sbaun 188
FRE TETEH CCS Rep e eere care at eo ani Resid Pe ee A HH ae 189

INTRODUCTION

The Namibian branchiopod fauna was first investigated by Barnard (1924). He
reported seven Streptocephalus species after extensive collecting, mainly in the Kaoko-
veld and Ovamboland areas. An eighth, and the only endemic species of the genus,
S. kaokoensis, was described by Barnard in his 1929 review of the southern African
branchiopods. Curtis (1991) listed the same eight and one additional unidentified
streptocephalid species in a checklist of the freshwater macro-invertebrates of
Namibia. As part of a recent study of the African Streptocephalidae (to be published
at a later date), material from the State Museum, Windhoek (SMN), the National
Museum of Zimbabwe (NMZ), Bulawayo and from Barnard’s collection (South
African Museum (SAM), Cape Town) was examined. A number of specimens resem-
bling S. proboscideus Frauenfeld (1873) were found to be slightly different from the

183

Ann. S. Afr. Mus. 103 (3), 1993: 183-189, 2 figs.

184 ANNALS OF THE SOUTH AFRICAN MUSEUM

type description and from redescriptions and illustrations by Brauer (1877) and Bren-
donck (1990). Differences were most evident in male antennal and frontal appendage
morphology. In addition, the two morphological types were collected sympatrically at
two localities. This indicated that specimens of two distinct species, one undescribed,
were involved. In this paper male antennal, frontal appendage and cercopod morpho-
logy of the new species are described. The external structure of the resting eggs and
the distribution of the new species are also assessed. Finally, S. namibiensis sp. nov.
will be allocated to a group consisting of species with similar antennal and frontal
appendage morphologies.

MATERIALS AND METHODS

Specimens were drawn and prepared for scanning electron microscopy following
the procedures in Hamer & Appleton (1993) and the terminology used is from Bren-
donck (1990). Measurements were made using a graticule and are presented as total
body length (mean + standard deviation if n > 10) from the front of the head
(excluding the antennae) to the tips of the cercopods (excluding the setae).

TAXONOMIC DESCRIPTION

Family Streptocephalidae Daday, 1910

Streptocephalus namibiensis sp. nov.

Type material

Holotype. SMN 51312, 1 male (16 mm); collected by B. A. Curtis, 12 March
1988; Namibia, Bushmanland, Nyae-Nyae Pan (19°46’S 20°30’E).

Paratypes. SMN 51294, 46 males (13 + 1,0 mm) and 18 females (13 > 1,0 mm);
collected by B. A. Curtis, 12 March 1988, from grassy pool adjoining Nyae-Nyae Pan,
Bushmanland (19°46’S 20°30'E).

Other material

SMN 51056, 1 male (17 mm), 1 female (15 mm); collected by B. A. Curtis,
14 May 1986, from Namibia, Bushmanland, Etosha National Park, Onangombati
(18°45’S 14°50’E).

SMN 51318, 2 males (one with cercopods damaged, other 16 mm); collected by
B. A. Curtis, 13 March 1988, from Namibia, Bushmanland, Tsumkwe (19°34'S
20RI4E):

SAM-—5986, 4 males, 6 females, all in poor condition; collected by Miss Wilman,
date unknown, from Namibia, Gobabis (22°33’S 18°56’E).

SAM-A7299, 1 male (19 mm), 3 females (19, 19, 18 mm); collected by G. Hut-
chinson, 1928, from Transvaal, Benoni, Avenue Pan (26°11'S 27°15’E).

SAM-—7305, 3 males (20, 19, 17 mm); collected by Miss Schuurman, January
1929, from Transvaal, Heidelberg (26°30’S 28°22’E).

NMZ/Cr 9, many specimens, 14 males measured (20 + 1,0 mm), 17 females
measured (19 + 1,0 mm); collected by J. Peacock, 26 April 1972, from Botswana,
northern fringe of Makarikari Pan (20°S 25°E).

A NEW SPECIES OF STREPTOCEPHALUS FROM NAMIBIA
Description of male

185
Antenna. Lateral process (Ip) slender, ventrally curved and apically acute
(Fig. 1A). Median antennal process (mp) long (ratio to total body length 0,56: 1).

mp

= a ; ‘
p
th ms.
Si AS = eas
\s fi

OOO Roxx
OARS
} CXS YO “@o:*
RR AWS!
//

Fig. 1. Streptocephalus namibiensis sp. nov. A. Lateral view of left antenna and frontal appendage of
male. B. Dorsal view of cercopods. Bar scale = 1mm. Abbreviations: f = finger, fa = frontal

appendage, Ip = lateral process, mp = median antennal process, p = processes, p2 = process 2,
s = spur, th = thumb.

186 ANNALS OF THE SOUTH AFRICAN MUSEUM

Antero-medial surface proximal to hand with three slender triangular processes (p) of
unequal length (Fig. 1A). A large leaf-shaped process (p1) just proximal to hand on
medial surface (Fig. 2A) followed by a similar smaller process distally and another
(p2) on the lateral surface (Fig. 1A). Thumb (th) slender, folded proximally. Anterior
region of thumb with bend (Fig. 1A) and apically acute. Angle between proximal and
distal region of anterior part of thumb about 135°. Thumb spur (s) broad, apically

Streptocephalus namibiensis sp. nov. A. Medial view of right antenna of male. x 33.
B. Detail of teeth on dorsal margin of finger (medial view). x 117. C. Frontal appendage. x 66.
D. Egg morphology. x 248. Abbreviation: P1 = process.

A NEW SPECIES OF STREPTOCEPHALUS FROM NAMIBIA 187

tapered and separated from anterior part of thumb by prominent rounded triangular
tooth (Fig. 1A). Finger (f) approximately three-quarters length of thumb, recurved
and with pointed apex (Fig. 2A). Two teeth of equal height on dorsal margin of
finger, with distal tooth narrower (Fig. 2B). Finger with prominent inflation distal to
teeth (Fig. 2A).

Frontal appendage. Long (half length of antenna), slightly coiled, distally tapered
and apically bifid. Single row of short spiniform processes at base of frontal append-
age, splitting into two rows about one-third along length. Distal half with four rows of
irregularly arranged processes decreasing in size along length (Figs 1A, 2C).

Cercopods. Moderate length (in relation to total body length 0,16:1). Outer
margin not strongly curved, both margins with long, plumose setae along entire length
(Fig. 1B).

Egg morphology

Eggs angular, with large, regular pentagonal fields separated by broad, rounded
ribs (Fig. 2D). Diameter = 420 um.

Differential diagnosis

Although very similar in general appearance, S. namibiensis and S. proboscideus
have a number of characters that are clearly different. Streptocephalus proboscideus
has long digitiform processes on the anterior margin of the median antennal process
and a shorter second tooth on the dorsal margin of the finger. Streptocephalus nami-
biensis only has three, shorter slender processes just proximal to the hand and has two
teeth of equal length on the finger. In addition, in S. proboscideus, the frontal
appendage is more tapered and strongly coiled with less regularly arranged spiniform
processes and the distal thumb region is longer (ratio to total thumb length 0,43; in
S. namibiensis this is only 0,34). The egg shell of S. proboscideus is characterized by a
large number of complex polygons (Brendonck 1990) rather than the large, regular
and simple pentagons of the S. namibiensis egg.

Distribution
Streptocephalus namibiensis has, to date, been collected from four areas: the

Transvaal Highveld (South Africa), central Namibia (Gobabis), northern Namibia
(Bushmanland), and the Makarikari Pan area in northern Botswana.

Etymology

Streptocephalus namibiensis is named after the country from which the type speci-
mens were collected.

Habitat

The only data regarding the habitat of S. namibiensis are provided by Hutchinson
et al. (1932) for the SAM—A7299 specimens. These were collected from an open pan,
about one-third of a mile (approx. 0,5 km) in diameter, south-west of Avenue Station,
Benoni, which filled up after heavy rains in January 1928. On 5 May (presumably
when the fauna was sampled), the pan contained about 2 ft (approx. 0,6 m) of turbid
water and was largely unvegetated apart from four species of Lemna and some weeds

188 ANNALS OF THE SOUTH AFRICAN MUSEUM

and grasses in the shallow part of the east side. The fauna of the pan included Arcella
(Protozoa), five cladoceran species, one species of Ostracoda, and four copepod
species.

DISCUSSION

Due to the similarity between the antenna and frontal appendage of S. namibien-
sis and S. proboscideus, the Benoni (SAM-—A7299), Heidelberg (SAM-7305) and
Gobabis (SAM-5986) specimens were previously all described as S. proboscideus
(Barnard, 1929). Brendonck (1990), in his redescription of that species, noted the fact
that both Barnard (1929) and Brauer (1877) had illustrated large and, in Barnard’s
(1929) redescription, equal-sized teeth on the dorsal margin of the finger, rather than
the smaller, unequal teeth of S. proboscideus. The importance of the antenna and
frontal appendage in specific mate selection has recently gained interest (Belk 1991).
According to theory, even slight differences in (primary or secondary) reproductive
structures can indicate separate species. Based on several studies, it has also been sug-
gested that temporary pools are relatively isolated habitats, and that regular gene flow
between them may thus be restricted (Wiman 1979; Brendonck et al. 1990; Fugate
1990). Dispersal of species over large areas is most likely a rare event, occurring in
instances such as episodic flooding. Local adaptations and morphological changes
from the source population are likely and the possibility of immigrants neutralizing
these changes, small. Under these conditions, groups of species with a common basic
pattern of morphological features may be expected. This appears to have occurred in
the African streptocephalids, which can be divided into ten so-called species groups
consisting of species sharing a number of antennal and frontal appendage characters.
This division needs to be researched further but, at this stage, it provides a basis for
the investigation of streptocephalid evolutionary trends, interspecific relationships,
and possibly the zoogeography of the genus. Streptocephalus namibiensis can be allo-
cated to a species-group consisting of S. proboscideus and S. trifidus Hartland-Rowe,
1968.

Wiman (1979) found that, because of the isolated nature of temporary pool habi-
tats, the development of sexual isolating mechanisms in streptocephalids is rare and
that hybrids are common under laboratory conditions. In this context, the collection
of S. namibiensis and S. proboscideus from the same localities on two occasions
(SMN 51312, 51294) is interesting. No specimens with intermediate morphologies
were found and it appears that some form of isolating mechanism prevents the for-
mation of hybrids. No other case of members of the same species-group occurring
sympatrically is known.

ACKNOWLEDGEMENTS

The curators of the material in the SAM, SMN and NMZ are thanked for the
loan of material. MLH is in receipt of a post-graduate bursary from the Foundation
for Research Development, and LB is research assistant with the National Fund for
Scientific Research, Belgium, and research associate with the Koninklijk Belgisch
Instituut voor Natuurwetenschappen (K.B.I.N.). The staff of the Electron Microscope

A NEW SPECIES OF STREPTOCEPHALUS FROM NAMIBIA 189

Unit, University of Natal, Pietermaritzburg, assisted with the electron micrographs
and Prof. C. Appleton commented on the manuscript.

REFERENCES

BARNARD, K. H. 1924. Contributions to a knowledge of the fauna of South West Africa. IT. Crustacea,
Entomostraca, Phyllopoda. Annals of the South African Museum 20 (3): 213-228.

BarNarD, K. H. 1929. Contributions to the Crustacean fauna of South Africa. Annals of the South
African Museum 29: 181-272.

BELk, D. 1991. Anostracan mating behaviour: a case of scramble competition polygyny. Jn: BRAUER,
R. T. & Martin, J. W. eds. Crustacean sexual biology: 111-125. New York: Columbia University
Press.

Brauer, F. 1877. Beitrage zur Kenntniss der Phyllopoden. Sitzungsberichte der K. Akadamie der Wis-
senschaften 75: 583-614.

BrENDONCK, L. 1990. Redescription of the fairy shrimp S. proboscideus (Frauenfeld, 1873) (Crusta-
cea, Anostraca). Bulletin de l'Institut Royal des Sciences Naturelles de Belgique. Biologie 59
[1989]: 49-57.

BRENDONCK, L., THIERY, A. & Coomans, A. 1990. Taxonomy and biogeography of the Galapagos
branchiopod fauna (Anostraca, Notostraca, Spinicaudata). Journal of Crustacean Biology 10:
676-694.

Curtis, B. A. 1991. Freshwater macro-invertebrates of Namibia. Madoqua 17 (2): 163-187.

Dapay, E. 1910. Monographie systematique des Phyllopodes Anostraces. Annales des Sciences
Naturelles, Zoologie (4° serie) 11: 91-489.

FRAUENFELD, G. V. 1873. Zoologische Miscellen. Verhandlungen der Zoologisch-botanisch Gesell-
schaft in Wien 23: 183-192.

Fucate, M. 1990. Population structure and gene flow in Branchinecta. American Zoologist 30 (4)
(Abstract): 72A.

Hamer, M. L. & Appleton, C. C. 1993. Four new Streptocephalus (Crustacea, Branchiopoda, Ano-
straca) species from south-eastern Africa. Annals of the South African Museum 103 (2): 167-181.

HarTLAND-RoweE, R. 1968. A new species of Streptocephalus (Anostraca) from Rhodesia. Crustaceana
15: 319-321.

HutcHInson, G. E., Pickrorp, G. G. & SCHUURMAN, J. F. M. 1932. A contribution to the hydro-
biology of pans and other inland waters of South Africa. Archiv ftir Hydrobiologie 24 S: 1-154.

Wiman, F. H. 1979. Mating patterns and speciation in the fairy shrimp genus Streptocephalus. Evol-
ution 33 (1): 172-181.

6. SYSTEMATIC papers must conform to the International code of zoological nomenclature (particu-
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Names of new taxa, combinations, synonyms, etc., when used for the first time, must be followed
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Family Nuculanidae
Nuculana (Lembulus) bicuspidata (Gould, 1845)

Figs 14-15A
Nucula (Leda) bicuspidata Gould, 1845: 37.
Leda plicifera A. Adams, 1856: 50.
Laeda bicuspidata Hanley, 1859: 118, pl. 228 (fig. 73). Sowerby, 1871: pl. 2 (fig. 8a—b).
Nucula largillierti Philippi, 1861: 87.
Leda bicuspidata: Nicklés, 1950: 163, fig. 301; 1955: 110. Barnard, 1964: 234, figs 8-9.

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In describing new species, one specimen must be designated as the holotype; other specimens
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Holotype
SAM-—A13535 in the South African Museum, Cape Town. Adult female from mid-tide region, King’s Beach, Port Eliza-
beth (33°51’S 25°39’E), collected by A. Smith, 15 January 1973.

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SMITHSONIAN INSTITUTION LIBRARIES

"Wi

MICHELLE HAMER

&

LUC BRENDONCK

A NEW SPECIES OF STREPTOCEPHALUS

(CRUSTACEA, BRANCHIOPODA, ANOSTRACA)
FROM NAMIBIA