Order HALOCYPRIDA Dana, 1853

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Introduction

Halocyprids differ from myodocopids by having a leg-like fifth limb, and a reduced or absent seventh limb. Most ostracods in this group are planktonic. A detailed description of halocyprid morphology and a list of southern ocean halocyprids can be found at "An Atlas of Southern Ocean Planktonic Ostracods", http://deep.iopan.gda.pl/ostracoda/index.php. There are two suborders: Halocypridina and Cladocopina. The Cladocopina are distinguished by the lack of a sixth limb, and by distinctive muscle scars (which are either in a triangular pattern (three scars) or a half-rosette (15 scars)). There are three genera in the Cladocopina (Polycope, Metapolycope, and Polycopsis) but there are currently no known species from Australia. In the Halocypridina, 13 Australian species are known in two families - the Halocyprididae and Thaumatocyprididae.

Diagnosis

Carapace mostly 0.2–3 mm long, strong or weakly calcified, shape variable, elongate subquadrate, ovate or almost circular, without keel but sometimes with straight dorsal margin extended posteriorly into spine; sexual dimorphism inconspicuous. Anterior rostrum and incisure well developed (often above mid-height), weak, or absent. Valves smooth or ornamented; pits, reticulation, ribs, tubercles and spines may be present. Anterior infold without setae. Valve marginal zone with or without calcified inner lamella. Hinge adont or not developed. Valve overlap minimal. Adductor muscle scars numerous in approximately circular or irregularly ovate aggregation, or as few as 3 scars in tight triangular pattern. Normal pores simple. Female with 5–7 pairs of appendages and furca, plus relatively minute unpaired genital apparatus; male additionally with unpaired copulatory limb. Many with unpaired terminal process posterior to furca. Antennula 3–8-segmented. Antennal endopod 2–3-segmented, often forming a hook-like (but not reflexed) clasper in males; exopod 8–9-segmented. Coxal endite of mandibula well developed with one or more terminal teeth, basal endite a cusped tooth or absent; well-developed segmented endopod, exopod relatively small lobe with setae or absent; never branchial plate. Maxillula relatively short, exopod unsegmented and endopod 2–3-segmented. Fifth limb generally leg-like with well-developed endopod, or shortened with endopod representing single segment; exopod short, unsegmented with terminal seta, or represented by setae only; large branchial plate; no sexual dimorphism. Sixth limb either leg-like with well-developed jointed endopod, with or without small lobular, setiferous exopod, and with proximal branchial plate, or limb absent. Seventh limb, reduced or absent, not vermiform or annulated. Single male copulatory appendage with 1–2 parts. Eyes absent, Bellonci organ usually present, sometimes bifurcate.

ID Keys

A tabular key is presented in Cohen et. al., 2007.

Diagnosis References

Cohen, A.C., Peterson, D.E., & Maddocks, R.F. 2007. Ostracoda. pp. 417-446 in Carlton, J.T. The Light & Smith Manual: Intertidal Invertebrates from Central California to Oregon. Berkeley & Los Angeles : University of California Press 4.

Horne, D.J., Cohen, A. & Martens, K. 2002. Taxonomy, morphology and biology of Quaternary and living Ostracoda. Geophysical Monograph 131: 5-36 [30]

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