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Strongylocentrotus droebachiensis
Strongylocentrotus pallidus

Echinodea: Sea Urchins

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The sea urchin test (skeleton) is made up of many ossicles which bear movable spines. Apparently correlated with the evolution of a very rigid test, the internal body wall lacks a muscle layer. The regular sea urchins such as Strongylocentrotus usually live on hard substrates and feed by scraping off algae and encrusting animals with a complex organ called ‘Aristotle lantern'. This organ is made up of numerous calcareous ossicles, five of which function as teeth that never seize growing.

Irregular sea urchins, in contrast, burrow in soft sediments and are largely deposit feeders. In contrast to the regular urchins who have strong large spines, the irregular urchins have tiny but numerous spines and usually a much thinner test.

Only 11 sea urchin species are known to exist in the Arctic.

Page Author: Bodil Bluhm
Updated: Jan 20, 2011

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