Meeting Abstract
Featherstars – those crinoids that discard the postlarval stalk – constitute the majority of extant crinoid species and are prominent members of many coral reef and deep-sea assemblages. However, our understanding of relationships within the group remains hampered by rampant homoplasy and high intra-specific variability. Several recent molecular phylogenies have resolved some uncertainties but have suggested many clades without known synapomorphies. Although external morphology for this group is relatively well-documented, internal morphology is underexplored, in part due to the difficulty of applying traditional histological methods to crinoids. Here we present preliminary data from a survey of the internal anatomy of modern and fossil featherstars based on X-ray micro-computed tomography (μCT) and scanning electron microscopy. Emphasis is placed on the structure of the somatocoel (one of three paired coeloms in echinoderms) within the calyx. The crinoid skeleton, including the central plug and basal rosette, conforms closely to the shape of the somatocoel, allowing this structure to be preserved in fossil featherstars. The morphology of the somatocoel within the calyx is complex and relatively conserved within some families, making it a valuable new tool for classification. Potential synapomorphies for groups above the family level are discussed. The calyceal somatocoel is continuous with that in the arms and pinnules, and probably plays an important role in the crinoid circulatory system. μCT-based investigation of the internal anatomy of fossil featherstars may clarify uncertain taxonomic placements and allow the physiology of extinct taxa to be inferred.
