Haploniscus Richardson 1908

Haploniscus Richardson, 1908

Type species: Haploniscus bicuspis (Sars, 1877).

Diagnosis. Haploniscidae with pereonites 5–7 and pleotelson showing different patterns of fusion, posterior pereonites never free. Third peduncular article usually (but not always) with a prominent dorsal spine. Pereonite 7 normal, not reduced. Pleotelson with posterolateral processes short or produced.

Remarks. Lincoln (1985a, 1985b) treated several species of Chandraniscus (with free posterior pereonites) as species of Haploniscus. The latter genus is redefined in this study to accommodate only those species that have fused posterior pereonites. It is also important to point out that pereon fusion often exhibits sexual dimorphism, as originally discovered by Sars (1877). In the type species, Haploniscus bicuspis, females show fusion only between pereonite 7 and the pleotelson while in males all three posterior pereonites are fused with the pleotelson. Possibly males have a different locomotory adaptation for mating behaviour but this hypothesis can only be confirmed after observations on living specimens of this deep-sea species.