Sea Urchin

spherical sea creature with a spiny exterior

Sea urchins are small, spiny sea creatures of the class Echinoidea found in oceans all over the world. (The name urchin is an Old English name for the round spiny hedgehogs sea urchins resemble.) Their shell, which is also called the "test", is globular in shape and covered with spines. The size of an adult test is typically from 3 to 10 cm.
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Noun
1. shallow-water echinoderms having soft bodies enclosed in thin spiny globular shells
(hypernym) echinoderm
(hyponym) edible sea urchin, Echinus esculentus
(member-holonym) Echinoidea, class Echinoidea

Any one of numerous species of echinoderms of the order Echinoidea.
  

A small spiny marine invertebrate belonging to the phylum Echinodermata. It is a model animal for the study of fertilization and development. Because it is a spawner, its gametes can be
obtained in large quantities. Simple mixing of sperms and eggs causes synchronous mitosis and cytokinesis. Furthermore, its eggs are large and clear. Link to the Sea Urchin website.