Meeting Abstract
P2.104 Tuesday, Jan. 5 Cake sand dollars with combed tube feet: morphometry and phylogenetics of Indo-Pacific arachnoidid clypeasteroids RECCIA, L.**; MOOI, R.; California State Polytechnic Univ., Pomona; California Academy of Sciences, San Francisco rmooi@calacademy.org
The genus Arachnoides (Clypeasteroida: Arachnoididae) includes very flat, circular, sharp-edged sand dollars occurring on shallow-water sandy substrates in the Indo-Pacific. Unique among sand dollars, arachnoidid food grooves extend from the mouth to the apical system and are bordered by sometimes extensive fields of tube feet and spines arranged in highly regimented “combed” rows involved in food collection. Although some Arachnoides species occur in great abundance, few systematic analyses have been done on the group since its description by Leske (1778). The genus is surprisingly under-represented in collections, and its natural history and phylogenetics remain poorly known. Specimens are recorded from Australia to Papua-New Guinea in the east, and from the Philippines westward to Bangladesh. However, literature sources disagree on the actual range. This study uses basic morphometric differences in the overall shape of the known species, A. placenta (Linnaeus, 1858) and A. tenuis (H.L. Clark, 1938), to determine whether they exhibit variable morphologies throughout their ranges or if hitherto undescribed taxa exist. A. tenuis is restricted to Western Australia, but even within this distribution, variants exist that strongly suggest the presence of cryptic species. Upon determination of all terminal taxa, phylogenetic analyses can be performed not only on Arachnoides, but on the other genera in the family such as the New Zealand endemic, Fellaster, as well as Ammotrophus and Monostychia (the latter known only from fossils). A combination of morphometrics, phylogenetics, and biogeography can shed light on the evolution of these important sand dollars, focusing on the origins of their sharp, disk-like shape and peculiar combed arrangements of the spines and tube feet.
