REASSESSMENT OF BLASTOID (ECHINODERMATA) PHYLOGENY WITH INTERNAL CHARACTER DATA

Our research aim is to incorporate new internal hydrospire models into a phylogenetic analysis to better assess blastoid relationships. Blastoids possess internal respiratory structures (hydrospires) that are lightly calcified and well-preserved. These respiratory structures of Paleozoic echinoderms have been used as a basis of classification, but have rarely been reconstructed three-dimensionally for morphological examination. While external hydrospire expression provides the basis for classification of the two major groups (spiraculates and fissiculates), internal morphology of these structures has largely been ignored. Recent efforts have been made toward recreating the hydrospires in 3D space, allowing for detailed examination of the structures for further analysis.

The current understanding of blastoid evolutionary relationships has been progressing with reassessment of homologous elements and numerous species. The most recent phylogenetic hypotheses suggest that Spiraculata is polyphyletic, occurring multiple times within Fissiculata.Recent analyses suggest that the inclusion of hydrospire models into a phylogenetic hypothesis provided increased understanding of evolutionary relationships, however, this work was limited to solely spiraculate data. We expand upon this study by incorporating two additional spiraculate and two fissiculate species. These additional models aid in elucidating relationships between fissiculates and spiraculates as well as allow us to test more complex questions with the evolutionary framework.