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Hard shell purple bug at the coast of Puerto Rico
Thu, Feb 26, 2009 at 7:12 PM
I was staying at a hotel on the east coast of the island of Puerto Rico and went to the shore to look at the ocean at around midday. This thing was purple, had a hard shell, did not move at all, about 5 inches long and 3 inches wide. It was withing the rocks. This was in summer 2006.
Melyssa
East coast of Puerto Rico

Chiton

Dear Melyssa,
The creature in your photograph is a Chiton. Chitons are primitive marine molluscs that have shells composed of 8 plates. The shells provide protection against waves which enable Chitons to survive on stormy rocky coasts. Chitons are sometimes called Sea Cradles.

Comment:
Sat, Feb 28, 2009 at 5:58 AM
Hi Daniel, Ah, another mollusk! This is Acanthopleura granulata (Gmelin, 1791), the West Indian fuzzy chiton. The shell plates of this chiton are actually brownish and are usually very eroded. The pink/purple color on this one is due to a layer of encrusting calcareous red algae. For more info see the Wikipedia article (which I put together.) Best wishes to you,
Susan J. Hewitt

Comment Update:
Sun, Mar 1, 2009 at 4:43 AM
I wanted to add:
1. That these chitons do move around, but only at night, grazing on microscopic algae which grows on the rock surface. Each one returns to its same spot on the rock at the end of the night.
2. That the maximum size of this species is about 3 inches in length.
3. There is a really excellent book on the chitons of P.R. called “Los Quitones de Puerto Rico” by Cedar I. Garcia Rios.
Susan Hewitt

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