Thenaria (Acontiaria) whose acontia are provided with basitrichs and microbasic p-mastigophors. Uppermost part of column with longitudinal muscles. Cinclides in the middle of the body, margin tentaculate. Sphincter mesogloeal, but very weak, so that the upper part of the body is not able to cover the tentacles. Mesenteries not divisible into macro- and microcnemes. Six, rarely eight, pairs of mesenteries perfect and fertile.
Definitions and contained taxa are those of Oscar Carlgren as published in 1949 : Kungl Svenska Vetenskapsakadamiens Handlingar, Series 4, Volume 1, Number 1
Electronic version made possible by NSF grant DEB95-21819 in the PEET program to D. G. Fautin.