Monoplacophorans
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Class: Monoplacophora

This is a group represented by some twelve known species, found off the west coast of Costa Rica. Prior to the discovery of the genus Neopilinia in 1952 the entire class was believed to have become extinct in the Paleozoic (the era before the rise of the dinosaurs).


This figure shows the upper (left) and lower (right) views
of the rare deep-sea Neopilinia, the only known living monoplacophoran. 
Photo by Dr. Robert Sprackland

    The members of the class that still survive have a single, clam-like shell and a snail-like body. They range in size from 3 to 30 mm (0.25 to 1.3 inches) across. They bear five pairs of gills.