Chitons on Bermuda
July 15, 2005
Provided and copyright by: Rob Sheridan
Summary authors & editors: Rob Sheridan
This photograph was taken on the rough south coast of Bermuda, where limestone formations are constantly battered by the long fetch of the Atlantic Ocean. The entire 22 square mile (57 sq. km) island (a British colony) of Bermuda is essentially a limestone cap on an extinct, undersea, volcanic mountain chain. It was last active about 100 million years ago, when the early Atlantic Ocean was in the midst of its expansion. Limestone intertidal rock characterizes many islands of the Caribbean as well as Bermuda. Its rough porous surface, clearly visible in this photograph, makes it ideal for the growth of algae. The relative ease with which it erodes results in many complex depressions (and sandy beaches!), which help protect Chitons from predators and rough seas.
Talk about survivors! Chitons are primitive mollusks that evolved initially during the "Cambrian explosion" at the start of the Paleozoic era, approximately 500 million years ago. As a species, they've survived with little change, through continental migrations (such as the creation and breakup of Pangea) and mass exterminations (such as the "Permian extinction" that closed the Paleozoic era about 240 million years ago). Through all this, they've been munching away at the algae growing on intertidal rock, oblivious to the evolution and activity of Homo sapiens. In this photograph of the West Indian Chiton (Chiton tuberculatus), the characteristic 8 plates and surrounding mantle are clearly visible. Except for the coin and the foot, this photograph could have been taken millions of years ago, on the tropical coast of Pangea, during the Paleozoic Era.
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