Hydroniscus malyutinae, George, 2004

George, Robert Y., 2004, Deep-sea asellote isopods (Crustacea, Eumalacostraca) of the north-west Atlantic: the family Haploniscidae, Journal of Natural History 38 (3), pp. 337-373 : 361-363

Hydroniscus malyutinae n. sp.

(figure 13)

Diagnosis. Hydroniscus with the cephalic rostral lobe small and conical. Fourth pereonite broader and longer than any of the anterior pereonites. Pereonites 5–7 completely fused with pleotelson with barely any sign of lateral suture. Pleotelson without any posterolateral projections, and posterior margin truncated. Antenna 1 with a flagellum of eight articles. Antenna 2 with a flagellum of 16 articles. Uropod uniramous and ventral, not visible dorsally.

Material examined. Holotype: male, length 2.8 mm, maximum width 1.1 mm. USNM Cat. No. 138681.

Type locality. R / V Eastward Sta. G-7814, site Beta over the Carolina lower slope .

Etymology. This new species is named in honour of my friend the Russian isopod researcher Dr Marina Malyutina of the Institute of Marine Biology, Vladivostok.

Description. Body about 2.5 times as long as wide, maximum width at the anterior margin of the consolidated pereonite segements 5–7. Cephalon with a small conical rostral lobe. Pereonites 1–3 subequal. Pereonite 4 longer and broader than any of the anterior three pereonites, with sharp anterolateral and posterolateral angles. Fused posterior three pereonites and pleotelson in the form of a shield.

Antenna 1 about half the length of antenna 2, with 12 articles, including peduncle and flagellum, terminal seven articles each bearing a single aesthetasc. Antenna 2 with four broad basal articles, second article being the shortest, flagellum composed of 16 articles, proximal ones broader than long, only the distal ones bearing setae. Antenna 2, when inflexed, reaching pereonite 4.

Male pleopod 1 proximally broad, narrow in the middle, distal part with inner and outer lobes, the inner lobes each bearing two setae. Uropods ventrally inserted, not visible dorsally, not reaching the posterior truncated margin of the pleotelson.

Remarks. This new species resembles H. abyssi Hansen, 1916 from the high latitude north-west Atlantic in having pereonites 5–7 and the pleotelson fused into a single segment without any sign of fusion along the lateral margin and in the absence of any sharp posterolateral angles to the pleotelson. However, the rostral lobe in this species is much reduced, and this and the presence of a large lateral suture between pereonites 4 and 5 clearly distinguish this new species. Furthermore, the pleotelson apex is truncated in H. malyutinae , but not truncated in H. abyssi . The north-west Pacific species H. vitjazi Birsten, 1963 also has a consolidated segment of pereonites 5–7 fused with the pleotelson without any sign of fusion along the lateral margins. Hydroniscus vijazi has small and sharp posterolateral pleotelson angles but in H. malyutinae posterolateral projections are lacking.