Bauer et al.—Blastoid hydrospire morphology
Description.—Five folds in each group; fold groups tightly packed making it difficult to distinguish folds in model; original peels provide a clear distinction of each fold; hydrospire cleft thin and elongate to accommodate each of five folds with apparent increased length around center of the specimen, tapering toward summit; each fold group (five folds) merges into single canal, then adjacent canals (separate lancet plates) merge to form single large spiracle opening. Folds narrow but numerous; fold groups at same lancet plate begin close together and angle out slightly, increasing toward top, where fold group approaches fold group from adjacent lancet plate. Anal area reduction present in P. godoni and anal area spiracles confluent with anus forming anispiracle, ending with five openings on summit.
Remarks.—Pentremites godoni is placed within the family Pentremitidae; no other models currently exist for this group. The model for P. godoni is incomplete, missing the lower portion of the theca; the spiracle and anal openings are clear in the model. The sectioning process was likely terminated because the portion that had already been sectioned was enough to address what was being investigated. It should also be noted that although this is an individual within the species P. godoni, it has been noted that fold number is variable within a species. The extent of the hydrospires through the theca is not clear as a large portion of the specimen is missing from this reconstruction. As with the other models, it appears that the hydrospire
canal is migrating toward the center axis. Unfortunately, since this is only the top of the specimen, it is not clear whether the remainder of the structure would follow a similar pattern to the other models. Each hydrospire pore leads to four (in the anal area) or five folds, which form a single canal near the summit and finally combine with an adjacent fold group to produce a single spiracle. The folds of P. godoni are narrow but numerous, unlike any of the other models.
Acknowledgments
We thank J. Sprinkle, T. Dexter, I. Rahman, J. Jin, and an anonymous reviewer for constructive comments that helped us improve this manuscript. L. White generated the models discussed in this paper, and both she and B. Nguyen taught the authors to properly visualize the structures in three dimensions. We also acknowledge ROA grants to Appalachian State University from NSF DEB 1036260 and the Appalachian State University Foundation, which supported this project and the aforementioned students. Naturalis Biodiversity Center in Leiden, Netherlands, provided access to specimens housed in their institutions. This study was supported by The University of Tennessee Discretionary Funds (J.E.B.). This paper is a contribution to Progress in Echinoderm Paleobiology.
Accessibility of supplemental data
Supplemental data available from the Dryad Digital Repository: doi:10.5061/dryad.1d1m6.
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