Abstract

The external expression of hydrospires in blastoids has provided a basis for major and minor group classification in the clade for over a century. Unfortunately, the complete anatomy of the hydrospires has never been comprehensively studied. This study examined and described the internal hydrospires of six spiraculate species by digitally extracting hydrospire data from a legacy data set of serial acetate peels. Although only six models have been currently generated, hydrospire morphology is variable both within and between previously escribed spiraculate families. Hydrospires were found to possess novel characters that were incorporated into a phylogenetic analysis of the six digitally modeled species and several related species. The addition of internal morphology into the phylogenetic analysis provides further resolution between groupings of blastoids.

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