Athyonidium

Deichmann, 1941

1 species

Large forms 25 cm or more with thick soft skin and numerous stout feet. Tentacles 20 in two circles of 10 each as 5 large external pairs and 5 smaller inner pairs. Calcareous ring with 5 stout almost rectangular radials and 5 insignificant interradials, often completely concealed in the tissue. One large dorsal stone canal, often branched and one or two tufts of smaller stone canals with minute heads. Numerous tufts of branched Polian vesicles. Inner anatomy seems otherwise typical of family. Spicules large well developed end plated, a few perforated spinous rods; tentacles with a few rosettes in younger individuals. Color grayish mottled to almost black, ventrum paler, tentacles dark. (Pawson??, 1970?)

* (Heding & Panning, call this genus Eucyclus). (Pawson??, 1970?)