Actinostolidae with well developed basal disc. Column thick, smooth. Sphincter, tentacles, oral disc and siphonoglyphs as in Sicyonis, the number of tentacles, however, the same as that of the mesenteries. Arrangement of mesenteries probably recalling that of Sicyonis, but irregular owing to the alternation of isolated genital mesenteries with isolated complete ones. Mesenteries differentiated into stronger sterile and weaker fertile ones, the latter occurring only in the distal part of the body and without filaments.
S. elongata Hertwig 1888
Definitions and contained taxa are those of Oscar Carlgren as published in 1949 : Kungl Svenska Vetenskapsakadamiens Handlingar, Series 4, Volume 1, Number 1