The Echinoid Directory

Retzneiosoma Kroh, 2005, p. 14

Diagnostic Features	Apical disc unknown. Ambulacra trigeminate, with a single large element reaching the perradial suture and two small demiplates positioned centrally and abutting one another. Pore-pairs arranged in three series on the oral surface. Primary tubercles absent from adradial zone; on aboral side with one or two tubercles per plate. Ambulacra about half the width of interambulacra at the ambitus. Interambulacral plates with distinct membranous gaps on both upper and lower surfaces. No primary interambulacral tubercles interradially on aboral surface. Primary tubercles perforate and distinctly crenulate. Lantern aulodont with grooved teeth. Auricles narrow and forming fused arch. Spines hollow, tip possibly without hyaline cone?
Distribution	Miocene (Langhian), Austria.
Name gender	neuter
Type	Retzneiosoma jaseneki Kroh, 2005, p. 16
Species Included	Only the type species
Classification and/or Status	Euechinoidea, Echinothurioida, Echinothuriidae Monotypic.
Remarks	The distinct crenulation of tubercles in this genus separates it from all echinothurioids other than Kamptosoma and occasionally in some species of Asthenosoma. The distinct membranous gaps between plates of the test place this taxon in the Echinothuriidae. However, as well as its crenulate tubercles, it differs from Araeosoma by having much less pronounced membranous gaps between its plates, and denser tuberculation. Asthenosoma differs in lacking primary tubercles on its aboral plates. Calveriosoma lacks membranous gaps from its aboral surface and has primary tubercles on only every second or third ambulacral plate. Hapalosoma is morphologically the closest but its demiplates are adradial in position in the adapical part of the test. Kroh, A. 2005. Catalogus fossilium Austriae. Band 2 Echinoidea neogenica. Verlag der Osterreischen Akademie der Wissenschaften, Wien. 1210 pp, 82 pls.