Gonactiniidae with broad pedal disc. Column broader at the margin than at the base. Longitudinal muscle layer and nerve-stratum of the column well developed. No sphincter. Tentacles long, numerous, at the base a little constricted, at the apex not swollen. Oral disc wide, conical. Only 8 mesenteries perfect, 12 pairs of mesenteries fertile and with filaments. Weak sterile mesenteries without filaments in the upper part of the body. Retractors weak, diffuse, parietobasilar muscles weak. Cnidom: see the family. A single species:
P. simplex Carlgren 1891
Definitions and contained taxa are those of Oscar Carlgren as published in 1949 : Kungl Svenska Vetenskapsakadamiens Handlingar, Series 4, Volume 1, Number 1
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