Parathyonacta

Caso, 1984

1 species

This new genus reveals some similarities with Thyonella. Size small, 1.8-3.9 cm in extended specimens. Body wall thick, braced with ossicles. Tube feet with sucker, arranged in double rows along the ambulacra. In the interambulacra they occur irregularly. Tentacles 10, the two ventral smaller. Calcareous ring low, with posterior projections. Stone canal very large and thick, adhering to the dorsal mesentery. Madreporic body large and round. Polian vesicle single well developed and located ventrally. Retractor muscles large attaching at the posterior of the calcareous ring. Gonads attached posteriorly, well developed, situated in the middle third of the body. Ossicles of 5 principal types: 1). baskets or small baskets found in the external portion of the integument. 2). elongated or quadrangular biscuits in the outer part of the body wall. 3). buttons large and small in the wall of the tube feet. 4). large triangular plaques or in a spiral form, principally in the buccal tentacles, secondly in the internal layer of the body wall. 5). thick brace or clamp, compact, perforated, straight or curved in the tube feet and the buccal tentacles. (Caso, 1984)