Nyantheae [sic] with basilar muscles. Aboral end flattened and usually abherent [sic], distinctly differentiated from the column. Bodywall of variable appearance, sometimes divisible into different regions; often with verrucae, marginal spherules or pseudospherules, vesicles or other protuberances. Sphincter usually endodermal or mesogloeal, but sometimes there is no sphincter. Tentacles and mesenteries usually numerous, the former cyclically or radially arranged. Mesenteries rarely differentiated into macro- and microcnemes. Retractors weak or strong, rarely circumscribed. Acontia present or absent.
Stephenson (1921 p. 541) did not accept the subtribe Thenaria proposed by me, but divided the genera belonging to this group at once into two, Endomyaria and Mesomyaria, the latter including also the genera provided with acontia. As, however, some genera with acontia have no sphincter, it became necessary to set the genera with acontia apart, in a group of equal rank with the Endo- and Mesomyaria (see Stephenson 1935 pp. 28-9). But as I have pointed out several times, it is very doubtful whether the three groups include genera which are always genetically related to each other. For instance the family Aliciidae has certainly nothing to do with the other Endomyaria, but its origin may be found in the subtribe Boloceroidaria. The Mesomyaria also is, to my mind, not a genetically homogenous group, because the mesogloeal sphincter may sometimes have arisen directly from undifferentiated endodermal circular muscles of the column, sometimes from an already differentiated endodermal sphincter. That an endodermal sphincter can in fact become transformed into a more or less mesogloeal one can be seen in Isosisyonis [sic] alba (CARLGREN 1927 p. 54). I have now examined smaller specimens of this species and find that they have an endodermal aggregate sphincter. The Acontiaria also is probably not homogeneous. In support of this opinion the genus Nemanthus gives an instance. At the place where the acontia occur in this genus, organs have appeared which are partly different in structure from acontia. If, therefore, I retain these groups, it is for practical reasons and is only a provisional arrangement.
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