Observations on the Early Cambrian helicoplacoid echinoderms

Abstract

The Early Cambrian helicoplacoid echinoderms occur in the Cordilleran Geosyncline of western North America in strata correlated with the Atdabanian Stage of Siberia. Several higher taxa are recognized on the basis of inferred differences in the water vascular system, test organization, and external morphology. These are subclass Polyplacida Durham, with genus Polyplacus Durham; subclass Helicoplacida Durham and Caster, with n. family Helicoplacidae, type genus Helicoplacus Durham and Caster (with tubefeet emerging between two contemporaneous ambulacral plates); n. family Westgardellidae, with type n. genus Westgardella, type species H. curtisi (Durham and Caster) (with tubefeet emerging between two sequential ambulacral plates). The genus Waucobella Durham is also referred to Westgardellidae. Helicoplacus gilberti Durham and Caster, H. everndeni Durham, H. casteri n. sp., H. guthi n. sp., H. sp. a, and H. sp. b are assigned to Helicoplacidae. The genus Westgardella includes H. firbyi Durham, 1967, and W. blancoensis n. sp., in addition to the type species. No evidence of flooring plates separating the radial water vessel from the interior of the test is recognized. The mouth is at the top of the test in the interpretation adopted herein and not lateral as inferred by others; therefore, the ambulacral system is not triradiate. Illustration identified as Helicoplacus curtisi by Paul and Smith includes misidentified plates and should not be referred to this species.