CLONING BY OPHIUROID ECHINODERM LARVAE

Larvae of the brittle star Ophiopholis aculeata, common to the North P acific coast of the United States, and an unidentified species of ophi uroid, collected from waters off the eastern coast of Florida, undergo asexual reproduction of the primary larva to produce a secondary larv al clone. Generation of a secondary larva begins with the release of t he larval posterolateral arms, which are initially retained by the set tled juvenile. In O. aculeata, the released arms regenerate all the st ructures typical of the primary ophiopluteus. Tissue and energy reserv es required for formation of the secondary feeding larva appear to be supplied by the absorption and reorganization of part of the posterola teral arms. Various developmental stages of the unidentified ophioplut eus were collected from plankton samples taken off the coast of Florid a. These included just-released posterolateral arms, plutei, and metam orphosed juveniles with the posterolateral arms still attached. The id entification of regenerating arms from the plankton demonstrates that asexual reproduction by ophiuroid larvae is not restricted to a single , laboratory-cultured species. In both O. aculeata and the unidentifie d Atlantic ophiopluteus, cloning involves the dedifferentiation of pri mary larval tissue and a developmental progression similar to that fol lowed by the zygote, although it is not known whether the formation of the secondary larva follows the same pathway utilized by the primary larva or a novel developmental program. Asexually produced secondary l arvae of O. aculeata undergo metamorphosis, settle to the benthos, and initiate a tertiary larval generation, indicating that cloned larvae could be added to the population as long as environmental conditions c ould support a planktonic existence. This phenomenon represents an unu sual potential to increase the geographic range and the number of juve niles of a given parentage in future generations without additional re productive input from the adult.