REVISED PHYLOGENETIC HYPOTHESIS OF BLASTOIDEA (ECHINODERMATA)
This study of blastoid phylogeny incorporates approximately 40 ingroup taxa and 143 informative character states. All previously utilized thecal characters were reevaluated and revised to better characterize external morphology. New character data was included that discriminated specific aspects of morphology (e.g., ambulacra and anal area plating). We inspected changes in tree stability by including and excluding taxa and characters with a high degree of missing data, to identify areas of varying stability. In addition, a new suite of character data has been generated that describes the internal anatomy more fully, especially the respiratory structures (hydrospires) by generating 3-D anatomical models from serial sections of thecae. The majority of species, for which have internal anatomical models fit into a large grouping of spiraculates. We incorporated the hydrospire data into a subsampled dataset of the spiraculate grouping to further examine tree stability at a finer scale.
Major evolutionary relationships remain stable with the inclusion or exclusion of partial data; this includes a polyphyletic spiraculate grouping within the larger fissiculate clade. Minor relationships either collapsed or were more fully resolved. This improved phylogenetic hypothesis provides a sufficient framework to begin testing evolutionary questions on clade evolution.