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Saturday, December 2, 2017

Little ones

While conducting surveys in the rocky intertidal zone this afternoon, we encountered some very small juvenile Purple Sea Urchins (Strongylocentrotus purpuratus).  This one was only ~3 mm across.


Lotsoflux said...

"Cute" comes to mind, but doesn't seem quite the appropriate word with all those prickles.
This appears to be a very early adult stage. Do they just grow expansively or are there molt stages like crabs?

Jackie Sones said...

There's definitely something "cute" about juvenile marine invertebrates!

This is a tiny juvenile sea urchin, likely a few months old.

Unlike a crab that has an exoskeleton, sea urchins have an endoskeleton -- which means there's a thin layer of tissue covering the skeleton. In urchins, the endoskeleton is called a test. The test is made up of many small calcareous plates that fit together like a jigsaw puzzle. To grow, they add material to expand each plate, and they also add new plates. Pretty cool! (The spines also lengthen and become more numerous as the urchin grows.)

Thanks for the comment and question!

:) Jackie