Thenaria (Acontiaria) with strong mesogloeal sphincter. Mesenteries not divisible into macro- and microcnemes. Usually 6 pairs of perfect mesenteries, sometimes more, but they are never numerous. Perfect mesenteries usually sterile, rarely fertile. Nematocysts of the acontia basitrichs only. Cnidom: spirocysts, basitrichs, microbasic p-mastigophors. Usually the spirocysts are large and broad.
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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