Australia: The Land Where Time Began

A biography of the Australian continent 

Ontogeny of Cinctans - Stem Group Echinodermata - Revealed by a New Genus Graciacystis, form the Middle Cambrian in Spain

In this paper the authors¹ describe a new cinctan echinoderm, Graciacystis ambigua, gen.et.sp.nov. recovered from rocks of Cambrian Series 3 age of Spain, that they described based on more than 100 articulated specimens raging from 6-14.5 mm in thecal length. It is shown by this material that Graciacystis ambigua is hghly conservative in its thecal construction, though it is plastic in the thecal shape, having a fixed number of thecal plates and very limited addition of plates in the stele and ventral membrane through ontogeny. It was found that in the smallest specimens ventral swellings on marginal elements are absent, though it becomes gradually more marked throughout growth. It is shown by cladistic analysis that Graciacystis is a basal cinctan, and that is it more derived than Sotocinctus and the Trochocystitidae, and a is a sister group to a large clade formed by Sucocystidiae + Gyrocystidae. The determinate growth pattern seen in Graciacystis is the general pattern for all cinctans.

Sources and further reading

1. Zamora, Samuel, Imran A. Rahman, and Andrew B. Smith. "The Ontogeny of Cinctans (Stem-Group Echinodermata) as Revealed by a New Genus, Graciacystis, from the Middle Cambrian of Spain." Palaeontology 56, no. 2 (2013): 399-410.