Genus Ocnus Forbes & Goodsir, 1841

Diagnosis (after Thandar 2008). Body shape cucumber-like, spindle-shaped or slightly angular. Tentacles 10, mid-ventral two reduced. Tube feet in 1–2 rows per ambulacrum, mostly rigid and non-retractile, interambulacra naked. Plates of calcareous ring with anteriorly tapering projections and posteriorly notched. Body wall ossicles baskets and small, knobbed perforated plates/buttons, often with four primary holes, and in some species also large multi-layered plates. Tube feet with perforated plates and end-plates.