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| Crinoids | |
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| A Passion Flower feather star (Ptilometra australis) | |
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| Class: | Crinoidea Miller, 1821 |
The crinoids are a class of echinoderms. They have two forms, the sea lilies, stalked forms attached to the sea floor, and the feather stars, which are free-living.
All crinoids are marine, and live both in shallow water and in depths as great as 6000 meters. The basic echinoderm pattern of fivefold symmetry can be recognized, but most crinoids have many more than five arms. Crinoids have a mouth on the top surface that is surrounded by feeding arms.
The crinoids have a long history. They were the first echinoderms to appear in the fossil record, and have kept their early structure throughout their long career. They were extremely common in the Palaeozoic, and some rocks from the Carboniferous consist almost entirely of fossil crinoids.
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