ABSTRACT
The phylogenetic relationships of echinoids have attracted considerable interest due to their excellent fossil record, and to their popularity for studies of ecology, development, and molecular evolution. Several recent analyses have considered phylogenetic relationships among and within echinoid orders, based on adult morphology or various molecular criteria. In general, these analyses have produced consistent results (Smith, 1992, TREE 7:224). However, the molecular data base remains limited in size, and some groups have proven difficult to analyze based solely on adult morphology. I have begun to investigate the utility of echinoid larval morphology as a supplement to these more traditional approaches. I have analyzed relationships at three levels of resolution: among orders (Echinoidea), families (Clypeasteroida), and genera (camarodonts = Temnopleuroida + Echinoida). The results of the first two analyses using larval character matrices are consistent with recent cladistic analyses based on adult morphology, and provide additional support for these phylogenetic hypotheses. In contrast, analysis of camarodont relationships using a larval data matrix produced a topology different from previously published phylogenetic hypotheses; in addition, the larval data set supported the monophyly of only three out of six currently recognized families (see Figure, below). The larval tree is robust based on bootstrap anlysis. Trees calculated from larval and adult data sets can be reconciled simply by reversing the polarity of a few characters in the adult data set. Furthermore, the larval tree is fully consistent with divergence times based on fossil evidence. Thus, the topology calculated from larval data is probably closer to the “true” tree than that based on adult data. Together, these analyses suggest that larval traits can provide useful information about phylogenetic relationships in echinoids across a broad range of divergence times. Larval traits may provide a particularly useful complement to molecular studies in clades where adult morphology is relatively uniform, such as the cidaroids and camarodonts.
