SAND DOLLARS OF THE GENUS DENDRASTER (ECHINOIDEA, CLYPEASTEROIDA) - PHYLOGENETIC SYSTEMATICS, HETEROCHRONY, AND DISTRIBUTION OF EXTANT SPECIES

All of the previously described extant members of the genus Dendraster are reviewed in light of new information on their taxonomy, phylogeny , ontogeny, and distribution. Allometric and multivariate analyses, in conjunction with qualitative comparisons of test morphology and exter nal appendages, indicate that there are three valid living taxa: D. ex centricus (Eschscholtz, 1831), D. vizcainoensis Grant and Hertlein, 19 38, and D. terminalis (Grant and Hertlein, 1938). A neotype is designa ted for D. excentricus, and locations of type material given for the o ther species. None of the Dendraster species described by Clark (1948) are valid: D. rugosus and D. mexicanus are junior synonyms of D. vizc ainoensis, and D. laevis is actually the adult form of D. terminalis. Until now, the latter species was known only from juvenile material, b ut it is a Dendraster in which the gonopores appear earlier than in an y other large scutelline. Plate patterns, food grooves, spination, and podial spicules are figured and described for each species. A dichoto mous key is also provided. Known distributions are discussed in light of new data, particularly those concerning the occurrence of fossil De ndraster in the Gulf of California, where living species are unknown. Quaternary expansion of the genus is attributable almost entirely to t he northward movement of a single species, D. excentricus. Preliminary phylogenetic analysis of the living ta?ta suggests that D. excentricu s and D. vizcainoensis are sister taxa, and that D. terminalis is the sister to this clade. D. terminalis exhibits several features that can be interpreted as paedomorphic.