On the teeth of the Recent cassiduloid Echinolampas depressa Gray, and on some Liassic fossil teeth nearly identical in structure (Echinodermata, Echinoidea)

Markel, K.

Zoomorphologie 892: 125-144

1978


ISSN/ISBN: 0340-6725
Accession: 021492547

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Abstract
The young recent cassiduloid E. depressa has a lantern and teeth which are fully developed, but which never function because they disappear completely after metamorphosis. The lantern resembles morphologically that of the clypeastroid family Fibulariidae. The teeth are built-up of tooth elements, which have small primary plates, large lateral plates, and a cluster of prisms, and they are nearly identical to the teeth of fibulariids. The fine structure of teeth from liassic fossils was analyzed. This was the 1st investigation of the microstructure of fossil echinoid teeth. The teeth were well preserved, and had nearly the same structure as the teeth of Echinolampas. Teeth of cassiduloid-clypeastroid structure were already in existence in the Liassic. Echinoid teeth of the "clypeastroid type" (present in Cassiduloida, Clypeastroida, and in all probability in Oligopygoida), and those of the "regular type" (present in all recent regular echinoids and in all probability in Holectypoida) are distinguished. The wellknown aulodont, stirodon, etc., types of teeth and lanterns belong to the regular type. Teeth of the regulat type are highly complex in structure, and certainly cannot be the result of evolutionary convergence. Morphologically the clypeastroid type is the simpler one, and there is no indication that it is the result of secondary simplification. For this reason the anatomical features of the clypeastroid type of echinoid teeth are considered to be the more primitive. Contrary to the opinion of others, echinoids possessing a masticatory apparatus of the clypeastroid type are by no means descendents of stirodont ancestors.