The Uniqueness That is Manzanillo-Sea Urchins

2010 May 2010 Nature Terry Sovil

By Terry Sovil from the May 2010 Edition

This is a photo I took of a sea urchin displaying it’s anus. It’s unusual to catch them doing this, it’s usually at night and not very frequently at that. But here it is. The Urchin Anus photo is the main one. The Urchin Normal is what a sea urchin would normally look like. They have very sharp spines that are extremely brittle and will easily break off inside a wound. The spines are sharp enough to penetrate neoprene rubber etc. They are aware of your presence and will move the spines to point at an intruder and will actually follow a hand from side to side.

The bubble like thing on the top is part of their digestive tract. Their mouth is on the bottom and the anus is on the top. This is a common tropical urchin, genus Diadema. Here it is clearly displaying it’s everted anal sac which is used for gas exchange. While totally rude for any human to wave their anal sac around in the water, it’s common, and acceptable, for members of Diadema to evert their anal sacs.

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