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The echinoderm classes Stylophora and Homoiostelea: non Calcichordata

Published online by Cambridge University Press:  21 July 2017

R. L. Parsley
R. L. Parsley*
Affiliation:
Department of Geology, Tulane University, New Orleans, Louisiana, 70118, USA
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Abstract

Stylophora and Homoiostelea are the largest classes of the subphylum Homalozoa. They have also been placed in the Calcichordata but that position is herein rejected. Stylophorans are divided into two orders the Cornuta and Ankyroida: cornutes have asymmetrical thecae, aulacophores with stylocones and cover plates over the food groove that open widely; ankyroids have essentially bilaterally symmetrical thecae, aulacophores with styloids and in most the cover plates do not open widely. Epispires, cothurnopores, and lamellipores in cornutes are respiratory structures not atypical of early echinoderms and are only superficially similar to chordate gill slits. The superior and inferior faces of cornute and ankyroid thecae and the aulacophores are homologous. There is no evidence that ‘mitrates’ (most ankyroids) are inverted or their aulacophores(calcichordate tail) have been lost and re-evolved.

Homoiosteles are superficially similar to stylophorans: the column or stele resembles the aulacophore and the theca in younger genera develope distinct marginal and somatic plate patterns. The earliest homoiosteles are attached by a holdfast, at least in juvenile stages, and this fixation may have imprinted some morphological features on steles of vagile genera. Earliest homoiosteles share significant characters with coeval species of the eocrinoid Gogia and it serves as outgroup.

Cladograms for Stylophora and Homoiostelea were generated by NONA, a phylogenetic program for personal computers.

Type
Research Article
Information
The Paleontological Society Papers , Volume 3: Geobiology of Echinoderms , October 1997 , pp. 225 - 248
Copyright
Copyright © 1997 by The Paleontological Society 

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