Hemiocnus, Mjobo, Sifiso & Thandar, Ahmed S., 2016

Mjobo, Sifiso & Thandar, Ahmed S., 2016, A new genus and a new species in the sea cucumber subfamily Colochirinae (Echinodermata: Holothuroidea: Dendrochirotida: Cucumariidae) in the Mediterranean Sea, Zootaxa 4189 (1), pp. 156-164 : 157-158

Genus Hemiocnus n. gen.

Cladodactyla Grube, 1940:40 (partim).

Cucumaria Sars,1857:123 , Pl. 1 figs. 24–29. Théel, 1886:113; Koehler, 1921:155, fig. 106; Cherbonnier, 1956:20 (partim). Ocnus Panning, 1949:438 , fig. 33, 34 (partim).

Pseudocnus Panning, 1962:68 , fig. 13, 14 (partim).

Pseudocnella Thandar, 1987:288 , 289 (partim).

Diagnosis. A genus of Cucumariidae with tube feet scattered or confined to ambulacra. Tentacles 10, ventral-most two or a couple of others reduced. Calcareous ring simple, without posterior prolongations. Body wall deposits include large. complex, multi-layered, fir-cone-shaped plates often with one end denticulate, with denticles sometimes borne on a projecting handle-like structure, and knobbed plates/buttons; an external layer of crossshaped, incomplete baskets also present, though not always identifiable in the type species. In the new species (described below) rosettes and complete baskets present in addition to incomplete baskets whereas large plates are restricted to the anal region of some specimens. Tube feet with rods or plate-like rods. Tentacle and introvert ossicles include rosettes in addition to rods and plate-like rods.

Type species. Cladodactyla syracusana Grube, 1840 .

Other species included. Pseudocnella insolens ( Théel, 1886) ; H. rubrobrunneus n. sp.

Etymology. Since this genus is close to Ocnus it takes its name from it.

Remarks. The new genus is diagnosed in the cucumariid subfamily Colochirinae because of the presence of baskets of some form in the body wall of all species assigned to it. The new genus resembles Pseudocnella Thandar, 1987 and Ocnus Forbes & Goodsir (in Forbes, 1841) . However, Thandar (1987) transferred Pseudocnus syracusanus to Pseudocnella with some doubt because it shares some characters with each of the three species he assigned to this genus. It now appears that Pseudocnella is strictly a southern African genus in which the tentacles are of equal size and there are no buttons in the body wall. Hence P. i n s ol e ns (Théel) with its one or two slightly reduced tentacles and the presence of buttons in the body wall in addition to plates and rosettes in the tentacles cannot be classified in Pseudocnella . Hence it is here transferred to the new genus. Thandar (1987) did comment that it is different from the other two species of Pseudocnella . Further, DNA sequencing of this latter species also throws it out of the Pseudocnella group but this research is still in progress. Now, also included in the new genus is H. rubrobrunneus because it shares with the type species similar incomplete baskets and buttons in the body wall but differs in the presence of also complete baskets and rosettes and the absence of large complex, fir-cone-shaped, multi-layered plates in most of the body wall. Hemiocnus resembles Ocnus in the 8+2 arrangement of tentacles and the presence of rosettes in the tentacles. However, the two genera are distinct in that Hemiocnus , like Pseudocnella and Pseudocnus , usually has in its body wall fir-cone-shaped plates often with one end denticulate while Ocnus lacks plates of this form altogether. Further the baskets of Ocnus are described as deep and basically tri-radiate/ trilocular ( Rowe & Gates 1995) and not shallow and quadrilocular as in the new species.