Invertebrate Zoology: A Study Guide - T. A. Dauda 2014

Metazoa
Echinodermata
Class Echinoidea

The body is spherical or flattened (disc-shaped or Heart-shaped) (see Fig. 81, B). It is enclosed in a solid shell made of tightly joined calcareous plates, which bear slender, sharp spines in some forms and thick, blunt ones in others. On the underside of the body lies the Mouth, equipped with a specialized chewing apparatus—Aristotle's lantern—featuring 5 Teeth projecting from the mouth. The intestine terminates in an anus located at the apex of the body. Extending from the mouth to the upper pole of the body are 5 rows of shell plates with pores through which tube feet protrude. Using these, sea urchins slowly crawl along the bottom and rocks.

Sea urchins are benthic, sluggish marine animals inhabiting various depths of the sea. They feed on animal and plant matter. Their roe is used as human food, and their coelomic fluid possesses tonic properties.

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Fig. 81 Holothurian (A), sea urchin (B)



Last update: 13/08/2026

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