Cnidocyst morphology and distribution in Corallium rubrum (Cnidaria, Anthozoa)

Cnidocytes are the most specialized cells of cnidarians and the structural morphology of their capsules, the cnidocysts, has been recognized as an important taxonomic character within the phylum Cnidaria. Nevertheless, this character has been almost completely neglected by specialists of alcyonarians (Octocorallia), due mainly to the difficulties inherent in the examination of soft tissues lacking calcareous sclerites and the supposed homogeneity of the Octocorallia cnidome. Two different types of cnidocysts, holotrichous isorhizas and atrichous isorhizas, are described here for the first time from the Mediterranean red coral Corallium rubrum (L.) (Octocorallia). Proposed evolutionary trends of anthozoan cnidocysts are also discussed.