Exocoelactiidae with well developed base. Column smooth or somewhat nodular, thick-walled and vase-shaped. Margin tentaculate, undulating or drawn out in 12 or more lobes, which are more or less distinctly marked. Sphincter mesogloeal, weak, so that the upper part of the column cannot cover the tentacles. Tentacles fairly short to short, sometimes thickened on the outer side at the base. At least the 12 first tentacles, and sometimes at least some of those of the third cycle, are typically arranged; the other tentacles are set in two rows, forming triangular groups continuous with one another. The 12 inner tentacles (or a few more) are the largest and lie in the depressions between the disc-lobes. The outer tentacles decrease in size towards the apices of the lobes. The outermost tentacles communicate with the exocoels, the inner with the endocoels. Longitudinal muscles of tentacles and radial muscles of oral disc mesogloeal, at least the former placed near the endoderm. 2 broad siphonoglyphs and two pairs of directives. The pairs of the mesenteries of the 2 first cycles are normally developed, perfect and sterile. Each of the later pairs consists of a larger and a smaller mesentery, arranged bilaterally with the youngest pairs in the middles of the secondary exocoels. The stronger partner in each of these pairs is perfect and may be sterile, all the other mesenteries are fertile. Cnidom: spirocysts, basitrichs, microbasic p-mastigophors.
Polysiphonia tuberosa R. Hertwig 1882
E. valdiviae Carlgren 1928
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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