Trachythyoneflaccida, a new sea cucumber species from southern Angola (Echinodermata:Holothuroidea:Dendrochirotida:Cucumariidae) with key to the genus.

A new species of a cucumariid holothuroid, Trachythyone flaccida, is described from shallow water off the southern coast of Angola. This increases to 20 the number of species in the genus Trachythyone. The new species is characterized by a soft, barrel-shaped body, scattered non-retractile tube feet, and body wall ossicles comprising a superficial layer of cup-like baskets and a deeper layer of simple, smooth, multilocular plates; cross-shaped deposits may also occur. The new species appears most closely related to the subantarctic T. bouvatensis (Ludwig & Heding, 1935) and to the Brazilian T. crassipeda Cherbonnier, 1965. A key is provided to all species currently classified in this genus.