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Article and Photographs by David Denning
Madreporite
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This structure will be found on the top, or aboral (away from the mouth) surface of most sea stars. It is usually about 1/50 th of the diameter of the sea star’s arms, so it can be easily missed when you observe these echinoderms. When 18th century biologists studied sea stars closely with a microscope, they thought this structure looked like a miniature brain coral. Brain corals belong to a group called the madreporarian corals, so the name of this sea star structure became the madreporite. Sea water can pass through the madreporite and enter the animal’s water vascular system. The madreporite acts as an effective filter, keeping out floating particles and living organisms such as parasites that might harm the sea star.
This photograph shows the madreporite of the short-spined sea star, Pisaster brevispinus. At the edge of the madreporite, which is about 5 mm across, is a small isopod crustacean. |
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