326-2 SYSTEMATIC REVISION OF SPECIES CONCEPTS IN PLATYCYSTITINAE (PARACRINOIDEA: ECHINODERMATA): A MORPHOMETRIC AND COMPARATIVE APPROACH

Abstract:

Echinoderms are an extremely diverse phylum with a fossil record dating back to the Early Cambrian. Like most groups, echinoderms have long been the focus of taxonomic scrutiny, and taxonomic revisions are commonplace. Morphometric analyses combined with comparative approaches can inform these revisions, giving us a clearer picture of the true species/genus-level diversity in this group.

The Subfamily Platycystitinae (Class Paracrinoidea) has a long history of systematic revision at the species and genus levels, although some of these changes have been called into question due to lack of formal analysis and/or clear reasoning for revisions. Here, we reevaluate all species of Platycystitinae with particular focus on Platycystites fimbriatus, which was previously synonymized and is not currently recognized as a valid species, and Platycystites ovalis, which has a poorly defined species concept. Within this subfamily, we investigate traits that are diagnostic at the species level, reevaluate the validity of species and genus concepts, and provide justifications for previous taxonomic revisions that have not been explained in depth.

We measured 12 morphological characters and calculated an additional 3 traits across 108 specimens belonging to nine nominal species spanning three genera. These measurements were made from specimens located in museum collections. These taxa include Platycystites cristatus, P. levatus, P. faberi, P. ovalis, P. fimbriatus, P. sp. (Frest et al, 1979), Globulocystites infundus, G. rotundatus, and Arbucklecystis pyriformis. Measurements of morphological features include the number of thecal plates, the number of intercalated plates, thecal height, thecal width, thecal depth, periproct height, periproct width, length of right and left ridge (from mouth to facet), length of right and left ambulacral arm, and recumbent ambulacral width. Calculated traits include the number of total callus plates, the average callus plate width, and the average callus plate height. These traits were analyzed using multivariate statistical methods to capture morphological similarities and differences between taxa. We then examined the morphospace occupation of each taxon to inform systematic revisions in addition to comparative study of specimens. Preliminary results suggest that P. fimbriatus should be reinstated as a valid species and that Globulocystites and Platycystites constitute a single genus. However, additional data needs to be collected to inform the validity of P. ovalis.

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