SYMBIOGENETIC ORIGINS OF CNIDARIAN CNIDOCYSTS

Cnidarian cnidocysts may have been derived through symbiogenesis from organelles in protoctistans. In order to trace the course of cnidocyst evolution back to originary types, we have assembled a cnidocyst data base from information in the systematic literature. That database is n ow available to the public on the World Wide Web at http://www.pitt.ed u/similar to sshostak/cnidocyst.html. It contains the cnidomes, or cen sus of cnidocysts, for 809 species and measurements on lengths and wid ths of cnidocyst capsules. The present analysis of cnidomes in the dat abase suggests that cnidocysts belong to no less than two families. Me mbers of one family of cnidocysts are found in Anthozoa, whereas membe rs of both families are found in Medusozoa. Competition among cnidocys t families in the microcosm of organisms, in addition to the natural s election of cnidarians in their external environments, may have contri buted to the evolution and diversification of cnidarian cnidocysts.