Rhipidaster Sladen, 1889

Rhipidaster Sladen, 1889: 447 .

Rhipidaster (Xenorias) Fisher, 1913: 222 .

Xenorias Fisher, 1919: 451 .

Comments. It is argued herein that Xenorias Fisher, 1913 is a junior synonym of Rhipidaster Sladen, 1889 . Fisher (1913, 1919) differentiated Xenorias from Rhipidaster based on the position of the marginal plates, which he argued formed oblique rather than parallel chevrons (in Rhipidaster) with one another, touching by the inter marginal ends along the side of the ray. Re-examination of these plates on dry specimens showed that the superomarginal and inferomarginal plates were in contact with articulated ends intermarginally permitting flexure. Thus, both parallel and oblique marginal plate arrangements are possible, in many cases on the same arm of a single individual.

Although Rhipidaster was not included in the most phylogenetic revision of the Valvatacea (Mah & Foltz 2011), the possession of multiple arms suggests greatest affinity with Solaster or Crossaster (Fig. 1).