New interstitial species of the family thaumastodermatidae (Gastrotricha Macrodasyoidea)

Abstract

Studies of the marine mesopsammon in an area of the Norwegian west coast southwest of Bergen and a two months stay at Stazione Zoologica, Naples, in the spring of 1965 yielded five new species of the macrodasyoid gastrotrich family Thaumastodermatidae. One of these, Tetranchyroderma tribolosum Clausen, 1965 has already been described, and the present paper deals with the remaining four, Thaumastoderma ramuliferum sp. n., Platydasys mastigurus sp. n., Platydasys phacellatus sp. n. and Platydasys ocellatus sp. n. T. ramuliferum systematically bridges the gap between T. swedmarki Lévi and T. cantacuzeni Lévi. P. mastigurus and P. phacellatus both possess strong, composite posterior cirri, while P. ocellatus is distinguished by a pair of eye-spots and long dorsolateral and dorsal adhesory tubules. All the three new Platydasys species have dimorphous sperm, and a modified endpiece of the vas deferens is interpreted as a penis.