Isanthidae with cylindrical, elongated body. Column smooth without any kind of projections. Margin distinct. Sphincter mesogloeal, not strong. Tentacles hexamerously arranged, their longitudinal muscles ectodermal, as also the radial muscles of the oral disc. 2 siphonoglyphs and 2 pairs of directives. 6 pairs of perfect fertile mesenteries, with kidney-shaped retractors, the other mesenteries microcnemes. No more mesenteries proximally than distally. Cnidom: spirocysts, basitrichs, microbasic p-mastigophors.
I. capensis 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