Baby Urchin!

By Nicole Webster

This guy speaks for himself, and is another prize from Ceratostoma foliatum (leafy hornmouth) cleaning:

Credit: N Webster

Its a baby urchin! It is too small to determine the species, but there are three common urchin species found in this regions, the purple (Strongylocentrotus pupuratus), red (S. fransiscanus) and the green (S. droebachiensis) sea urchins. Colour is the main way to tell them apart, although some greens can be a bit purple-ish, and the reverse may also be true. Spine length and tube foot arrangement can also be used to try to distinguish species.

Here you can see the joints of where the spines attach to the test, and the tiny ossicles inside the tube feet ends. Credit N. Webster

Each spine on an urchin is independently moveable, and separated from the body (test) of the urchin by a small joint of tissue with muscles. In the presence of a predator, they can all point towards it to increase cost of attacking one.

I can hear you say aww! from here.

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