Achelidelphys nigra Lafargue and Laubier 1977

Achelidelphys nigra Lafargue and Laubier, 1977

Material examined: none.

Differential Diagnosis: Body highly transformed, stellate; segmentation indistinct with segmental boundaries marked by superficial folds. Cephalosome with frontal margin merging into tapering laterally-directed antennulary lobes. Rostrum anteroventrally-directed; inflated, simple elongate lobe, without accessory median lobe. Post-rostral median lobe absent. Labrum forming rounded, hemispherical lobe. Lateral margin of cephalosome not produced into ridge-like swellings. Antennomedial processes absent. Metasome truncated, with urosome hardly extending posterior to origin of leg 4. Legs 1–4 transformed, originating laterally, each occupying entire margin of somite; produced laterally giving body a stellate appearance. Mid-ventral metasomal process present between leg 2 only. Urosome vestigial, located terminally; bearing partly incorporated caudal rami. Surface of body, rostrum, labrum, cephalosomic processes, and legs densely ornamented with surface setules.

Antennules forming tapering lobe on either side of frontal margin of cephalosome. Antenna to maxilliped lacking. Legs 1–3 biramous; rami represented by unsegmented, tapering lobes; exopodal lobe laterallydirected, with broad base, carrying smaller endopod ventrally. Leg 4 uniramous comprising short, posterolaterally-directed lobe representing exopod. Oviducts tubular, containing eggs visible through body wall. Leg 5 absent.

Body length of female about 2.25 mm. Male unknown.

Remarks: The main character distinguishing A. nigra from A. steinitzi is the presence of only a single median ventral lobe, located between the second pair of legs in the former compared to two lobes, located between legs 2 and 3, in the latter. The oviducts are tubular and form loops within the body cavity in A. nigra but they do not form an expanded sac-like uterus as in A. ampla, or a multi-lobate uterus, as in all other Achelidelphys species.