Cloning by Ophiuroid Echinoderm Larvae.

Larvae of the brittle star Ophiopholis aculeata, common to the North Pacific coast of the United States, and an unidentified species of ophiuroid, collected from waters off the eastern coast of Florida, undergo asexual reproduction of the primary larva to produce a secondary larval clone. Generation of a secondary larva begins with the release of the larval posterolateral arms, which are initially retained by the settled juvenile. In O. aculeata, the released arms regenerate all the structures typical of the primary ophiopluteus. Tissue and energy reserves required for formation of the secondary feeding larva appear to be supplied by the absorption and reorganization of part of the posterolateral arms. Various developmental stages of the unidentified ophiopluteus were collected from plankton samples taken off the coast of Florida. These included just-released posterolateral arms, plutei, and metamorphosed juveniles with the posterolateral arms still attached. The identification 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 unidentified Atlantic ophiopluteus, cloning involves the dedifferentiation of primary larval tissue and a developmental progression similar to that followed 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 larvae 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 could support a planktonic existence. This phenomenon represents an unusual potential to increase the geographic range and the number of juveniles of a given parentage in future generations without additional reproductive input from the adult.