Halcampidae with smooth, cylindrical body without tenaculi, not divisible into regions. Sphincter very weak, mesogloeal, close to the tentacles. Tentacles more than 12. Longitudinal muscles of tentacles ectodermal. 2 weak but distinct siphonoglyphs. Mesenteries showing a distinct tendency to pentamerous arrangement, owing to the retardation of the development of a pair of the mesenteries of the first cycle on one side of the directive plane. Only 5 pairs of macrocnemes, the others microcnemes. Mesenteries somewhat more numerous than tentacles. Retractors of the macrocnemes very strong restricted, reniform to almost circumscribed. Parietal muscles not very strong. Cnidom: spirocysts, basitrichs, microbasic p-mastigophors.
H. teres Carlgren 1938
Definitions and contained taxa are those of Oscar Carlgren
as published in 1949 : Kungl Svenska Vetenskapsakadamiens Handlingar, Series
4, Volume 1, Number 1