views updated

Homalozoa (‘carpoids’; phylum Echinodermata) Extinct subphylum whose members have no trace of radial symmetry. The theca is depressed and asymmetrical. Homalozoa are known from Middle Cambrian to Middle Devonian rocks. There are three classes: Homostelea, Homoiostelea, and Stylophora. The affinities of the group have generated some controversy. The similarities between the larvae of some echinoderms and some chordates (Chordata) has led to the suggestion that the phyla are in some way related. Most recently, the Stylophora have been reassigned by R. P. S. Jeffries on morphological grounds to a new subphylum of primitive chordates, the Calcichordata. The matter remains unresolved.