Meeting Abstract
P2.129 Wednesday, Jan. 5 The Astriclypeidae: Phylogenetics of Indo-Pacific, super-flat, holey sand dollars JANSEN, N.**; MOOI, R.; U. of Pennsylvania, Philadelphia; Calif. Acad. of Sciences, San Francisco rmooi@calacademy.org
The Clypeasteroida contains about 250 extant species of sea urchins including the sand dollars (Scutellina). Among the latter is the Astriclypeidae, a clade characterized by large, flat sand dollars with holes (lunules), passing completely through the body. The type genus of the clade, Astriclypeus, has 5 lunules, but two other astriclypeid genera have only 2: the fossil genus Amphiope and Echinodiscus, an extant genus of large, very flat inhabitants of sandy beaches throughout the Indo-Pacific. Despite their conspicuousness and abundance, these sand dollars remain poorly understood. The genus currently houses 4 species: E. truncatus, E. tenuissimus, E. auritus, and E. bisperforatus. Preliminary work with oral plate patterns and pedicellariae suggested additional, cryptic taxa, providing impetus for a full revision of the genus using as many of the known specimens as possible. The original descriptions of E. auritus and E. bisperforatus are both likely to encompass multiple species. In order to determine whether the currently recognized species should be further divided, we examined plate architecture, morphometrics, and pedicellariae. The morphological differences among the proposed species were consistent with their distribution patterns, which lent more evidence as to which terminal taxa should be used to construct a phylogeny. Our analysis, based on the combination of morphological and biogeographic information, and relying on forms such as Astriclypeus as outgroups, allowed construction of a phylogenetic tree that included a total of 9 terminal taxa within the genus Echinodiscus. Using this tree, we were able to analyze the evolution of some of the more conspicuous and unusual features of this group, including bizarre, poison-bearing pedicellariae and the events surrounding the origin and diversification of the lunules.
