![]() The outer epidermis, a single layer of ciliated cells equipped with tiny moveable hairs (cilia) covers all external parts including all the appendages (spines and pedicellariae).Ī nerve network is situated beneath the epidermis but outside the test. The number of wedges of the primary spines seems to vary geographically, but most urchins up to a diameter of 65 mm have 23-27 wedges, some up to 33. Mamelons are smooth and they have an undercut neck: usually five in each arc, but occasionally six. ![]() Test has no depression or pits, has a five-point star pattern and it is made up of a series of plates interlocking into a solid almost spherical skeleton. The Green Sea Urchin is an example of regular urchin, which is radially symmetrical, either globular or ellipsoid, with the anus located within the plates of the apical system at the top and the mouth usually on the underside. The brittle “shell”, or test, is comparatively small, low but not flat, reaching a width of 8 cm the short blunt spines crowd close together and are 1 to 5 cm long. Identifying Features: The Strongylocentrotus droebachiensis sea urchin can appear dull green, yellow-green or, generally, greenish-brown: light green at base of the spines and lighter toward the tip vertical rows of tube feet usually appear as dark bands and the test is usually purple to violet rather than green. Size Range:the average adult size is 50 mm (2 in), but it has been recorded at a diameter of 87 mm (3.4 in). Scientific Name: Strongylocentrotus droebachiensis
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