Ocnus Forbes & Goodsir

Thandar, Ahmed S., 2008, Additions to the holothuroid fauna of the southern African temperate faunistic provinces, with descriptions of new species, Zootaxa 1697 (1), pp. 1-57 : 18

Genus Ocnus Forbes & Goodsir

Diagnosis (after Panning 1971, amended herein)

Body-shape cucumber-like or spindle-shaped or slightly angular. Tentacles ten, midventral two reduced. Podia in 1-2 rows per ambulacrum, mostly rigid and non-rectractile, interambulacra naked. Plates of calcareous ring with anteriorly tapering projections and posterior notches. Body wall spicules cups/baskets and small, knobbed perforated plates/buttons, often with four primary holes, and in some species also large multilocular and often multi-layered plates. Podia with perforated plates and end-plates.

Remarks

Ocnus was initially a large taxon but Panning (1971) restricted it to include only five species with baskets and oval, knobbed plates with small perforations, and sometimes also with reticulated plates, but without reassigning the other species which he included in Ocnus in 1949. Rowe (1970), in a paper more or less contemporary with Panning’s, already re-assigned several species with four-holed buttons, formerly included by Panning (1949) in the preoccupied genus Ludwigia to the genus Aslia . However, O’Loughlin and O’Hara (1992) are of the opinion that Rowe’s distinction of using four-holed buttons is rather arbitrary. Despite Panning’s (1971) and Rowe’s (1970) works several species formerly included in Ocnus and Luwigia still remain unassigned, some of which may require new genera as was done with several Australian species by O’Loughlin and O’Hara (1992) and O’Loughlin and Alcock (2000), a task beyond the scope of the current paper. For my purpose I have amended the diagnosis of Ocnus to also include those species with multilocular and often multi-layered plates in the body wall. This move retains Cucumaria capensis Théel, 1886 in Ocnus , and allows for the description here of a new species, O. rowei from South Africa.