Stolus kilberti, anew species from the east coast of South Africa (Echinodermata : Holothuroidea : Dendrochirotida) with a key to the genus Stolus Selenka

A new species of phyllophorid dendrochirotid, collected from subtidal water s off the east coast of South Africa, is described as Stolus kilberti sp. n ov. in the subfamily Thyoninae. It is distinctive in the form of its calcar eous ring and body wall plates in combination, and appears to be closely re lated to S. rapax (Koehler & Vaney, 1908) from the Bay of Bengal, differing from it in having elongated. rather than spherical multi-layered plates. I f the calcareous ring were not fragmented the species could well be referre d to the genus Pseudothyone Fanning, 1949 of the subfamily Sclerodactylinae , closely allied to P. mosaica (Koehler & Vaney, 1910) from the Persian Gul f. The remarkable similarity in the body wall deposits of genera currently classified in two separate subfamilies challenges the use of the calcareous ring to separate subfamilies, since it demands a degree of evolutionary co nvergence which hardly seems probable. Of the eleven nominal species of Sto lus, eight are keyed and a table provided to compare the three similar spec ies - S. kilberti, S. rapax and P. mosaica.