Of Shear Force and Shingles

What good is a sea urchin without spines? Well, I'll tell you.

Here you've got the Indo Pacific Shingle (or Helmet) Urchin (Colobocentrotus atratus). According to Echinoblog (great site, folks), they are found in rocky intertidal areas of the South and Central Pacific. What benefit does having a helmet-shaped body serve this sea urchin? Turns out that their native waters can flow at high rates, and their shape offsets the effects of shear force.





















But the true power of this little beast is seen only when you upend one. Take a look at those tube feet (especially in the last photo). They enable the shingle urchin to withstand water flows of a couple magnitudes greater than your spiny urchine. Those spines won't do you much good if you're swept away with the current, Mr. Spiny Urchin. Nope, best to keep a low profile, like Mr. Shingle Urchin.

Thanks for the uchin, Jelo.