MCEDWARD, L.R.*; MINER, B.G.: Diversity and evolution of larval patterns in ophiuroid echinoderms
Ophiuroids have three larval types: ophiopluteus, vitellaria, and doliolaria, as well as direct developing mesogens. There are four developmental patterns : planktotrophy, pelagic lecithotrophy, benthic lecithotrophy, and direct development. Lecithotrophic development is phylogenetically widespread and occurs in more families (10 of 11) than does planktotrophy via an ophiopluteus (5 of 10 families). In most species with planktotrophic development, the pluteus is the final larval stage, but in one species, Ophiocoma pumila, the ophiopluteus transforms into a pelagic, nonfeeding doliolaria at the onset of metamorphosis. Pelagic lecithotrophic development occurs via a reduced pluteus or a doliolaria larva. Benthic development involves a reduced pluteus that metamorphoses before hatching, or a brooded vitellaria or mesogen. The ancestral ophiuroid life cycle probably involved planktotrophic development via an ophiopluteus larva, followed by a pelagic, lecithotrophic doliolaria larva. Assuming that the loss of a feeding larval stage is irreversible, then nonfeeding larval development must have evolved at least 10 times. Benthic development must have evolved at least 9 times. Direct development has evolved at least twice in the class. The doliolaria stage has been lost at least 3 times, and the pluteus has been lost a minimum of 9 times. There is a confusing array of possible evolutionary transitions that could account for the diverse derived life cycles and larval stages of ophiuroids. Several developmental patterns could have evolved by alternative routes and if evolved repeatedly, by multiple routes. Unfortunately, the developmental diversity of the ophiuroids is too poorly known to confirm or eliminate most of these possibilities.