Column smooth or with vesicle-like outgrowths and with very weak longitudinal ectodermal muscles. Sphincter very weak or absent. Tentacles simple, few to fairly numerous, not retractile, their longitudinal muscles ectodermal as also those of the oral disc. Actinopharynx very short, little differentiated from the oral disc, or quite well developed, with longitudinal muscles. Siphonoglyphs present, distinct or absent. Perfect pairs of mesenteries 6-12. Mesenteries regularly or more irregularly arranged. Retractors weak. All or almost all mesenteries fertile.
Definitions and contained taxa are those of Oscar Carlgren as published in 1949 : Kungl Svenska Vetenskapsakadamiens Handlingar, Series 4, Volume 1, Number 1