Haliactiidae with long, vermiform body divisible into 3 indistinct regions, a more or less physa-like base, a scapus provided with longitudinal rows of cinclides and a capitulum. No sphincter. Tentacles numerous, those of the last cycles atypically arranged in as much as the youngest tentacles are situated nearer the mouth than the next youngest. Longitudinal muscles of tentacles and radial muscles of oral disc ectodermal. Mesenteries divisible into macro- and microcnemes, more numerous at the margin than at the base. 6 pairs of perfect mesenteries with retractors, filaments, gonads and acontia, microcnemes without these organs. Retractors strong, restricted, more or less reniform. Acontia well developed, atypically arranged in as much as several may arise from each macrocneme. Acontia with basitrichs and probably microbasic amastigophors (penicilli).
P. Ramunni [sic] Panikkar 1936
Definitions and contained taxa are those of Oscar Carlgren
as published in 1949 : Kungl Svenska Vetenskapsakadamiens Handlingar, Series
4, Volume 1, Number 1