From these observations and other evidence, biologists have concluded that echinoderms probably evolved from an ancestor with bilateral symmetry - perhaps a worm allied to the bryozoans or their ancestors. Most echinoderms spawn directly into the sea. The fertilized eggs develop through several microscopic swimming stages, and in manny species these larvae feed on smaller plankton for several weeks before the animal is ready to settle to the bottom. About our video program on Phylum Echinodermata. This material may be copied for use in student classroom projects and reports.
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