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(O.F Müller, 1776)

Northern Sea Urchin

Description
Test low, arched, not flattened; up to 80 mm in horizontal diameter. Colour of test mostly greenish-brown, the spines greenish or reddish, sometimes violet, often with whitish point.

Test
Test without depressions or pits. Buccal plates without spines; gill-cuts small and obsolete. Usually 5-6 pore pairs in each ambulacral plate (polyporous)(S. droebachiensis test).

Spines
Test closely set with spines of uniform length, the primaries not very conspicuous. Each ambulacral plate carries a primary spine. These primary spines form vertical series. In larger specimens, also the secondary ones form vertical series.

Pedicellariae
Globiferous pedicellariae fairly large and conspicuous, usually with numerous spicules arranged in a band along the sides of the blades (S. droebachiensis pedicellaria). The blades without lateral teeth, the outer part forming a closed tube. Tridentate pedicellariae usually with rather broad, leaf-shaped blades.

Habitat
Although it is a littoral species, which may bore holes in the rocks, it is found till depths of 1200 m.

Distribution
In the North Sea the species occurs from the Shetlands to the southern part of the North Sea. Elsewhere it is distributed from the Siberian Sea and Spitzbergen to the Sound, from Iceland and Greenland to New Jersey, and in the Northern Pacific to Vancouver and Korea.

Remarks
This sea urchin is more robust than Psammechinus miliaris. Its distribution does not show overlap with that of Paracentrotus lividus.

Northern Sea Urchin (Strongylocentrotus droebachiensis)