Revision of the unusual Carboniferous ophiuroid Cholaster (Echinodermata) and remarks on skeletal differentiation within the Asterozoa

Newly discovered, relatively well-preserved specimens of Cholaster whitei n. sp. (Ophiuroidea, Echinodermata) are described from a small area of extensive outcrop of the Bangor Limestone (Mississippian, Chesterian) exposed on the edge of Cedar Creek Reservoir in northern Alabama, USA. The only other known species of the genus, C. peculiaris Worthen and Miller, is based on a single specimen exposed in dorsal aspect and collected from strata of similar age from southwestern Illinois. Incomplete preservation of the single C. peculiaris specimen limits comparisons, but differences between the two occurrences support separation at the species level. Skeletal remains of both asteroids and ophiuroids are first recognized from Early Ordovician sediments, and representatives of the two classes have retained plesiomorphies or converged morphologically since that time, thereby suggesting important evolutionary potentials and limitations. Cholaster is asteroid-like and unusual among ophiuroids in that the arms are comparatively broad and strap-like, and lateral ossicles are similar to asteroid adambulacrals and marginals, whereas the vertebrae (i.e., fused axial pair) and oral frame configurations of C. whitei n. sp. are typical of the Ophiuroidea. The oral frame of C. peculiaris is unknown. A poorly preserved specimen of the asteroid Delicaster? also was recovered from nearby strata associated with the C. whitei n. sp.