Elongate Haloclavidae with a physa-like aboral end which can flatten into a disc. Column smooth with vertical rows of cinclides in its upper part. No sphincter. Tentacles 24, the inner shorter than the outer ones?, their longitudinal muscles ectodermal. A single siphonoglyph without a conchula. All mesenteries macrocnemes. The fifth and sixth couples weaker than the 8 other mesenteries of the first cycle. Only the six primary pairs usually fertile. Retractors and parietal muscles of the older mesenteries strong, the former reniform. Cnidom: spirocysts, basitrichs, microbasic p-mastigophors.
H. attenuata Torrey 1902
Definitions and contained taxa are those of Oscar Carlgren
as published in 1949 : Kungl Svenska Vetenskapsakadamiens Handlingar, Series
4, Volume 1, Number 1