Article: Somasteroidea, Asteroidea, and the affinities of Luidia (Platasterias) latiradiata
Important changes in the taxonomy and phylogenetic interpretation of stellate echinoderms were proposed during the 1960s by H. B. Fell; certain of this author's ideas are re-evaluated. Fell argued that the extant west American sea star Platasterias latiradiata Gray is a surviving member of the otherwise Palaeozoic Somasteroidea. The extant family Luidiidae was considered primitive among true asteroids and it was included with the Palaeozoic family Palasteriscidae in the order Platyasterida. The skeletal arrangement of Platasterias and Luidia was interpreted as having been derived with relatively limited change from a currently unknown Cambrian crinoid ancestry. It is argued here that Platasterias is not a somasteroid but a subgenus of Luidia, and the Luidiidae is returned to the large living order Paxillosida. The origin of the morphology of Luidia, including Platasterias, is related to sea star behaviour and habitat rather than a crinoid ancestry. The Luidiidae is not considered to be of major importance in delineating asteroid phylogeny.