BLASTOIDEA: RECONSTRUCTING THE ECHINODERM TREE OF LIFE

Since the recognition of Blastoidea as a distinct group of echinoderms, paleontologists have proposed many different classification schemes and phylogenetic relationships. Until now, phylogenetic inferences have been made utilizing relatively few characters, limited taxon sampling, and a lack of rigorous methodologies. Even though progress has been made, blastoid evolutionary history is still unresolved and many questions still persist. A ground up phylogenetic study of Blastoidea was conducted as part of the Assembling the Echinoderm Tree of Life project, to provide a robust, baseline phylogenetic hypothesis for the clade. This parsimony analysis included 21 ingroup taxa and three outgroup taxa coded for 49 characters and 139 character states. Taxa were coded using exemplar species drawn from across blastoids to cover most of the major proposed lineages. All characters were unordered and equally weighted. A branch and bound search retrieved two most parsimonious trees of with a tree length of 107 steps, consistency index of 0.53, and retention index of 0.73. In our analysis the Ordovician Macurdablastus codes as a fissiculate blastoid based on the manifestation of respiratory structures and lack of spiracles. Because Macurdablastus is sister taxon to Troosticrinidae, spiraculates are polyphyletic being derived twice on the tree from a paraphyletic Fissiculata. Non-troosticrinid spiraculates form a clade. Nucleocrinids, schizoblastids and the granatocrinid Mesoblastus form a clade that is sister taxon to a clade containing the granatocrinid Granatoblastus nested within Orbitremitidae (paraphyletic), Diploblastidae and Hyperoblastidae. These two clades form a monophyletic group that is sister taxon to a clade containing Ambolastomatidae and Pentremitidae. Non-Macurdablastus fissiculates form a clade. Astrocrinids and neoschismitids form a clade that is sister taxon to a clade containing codasterids nested within a paraphyletic Orophocrinidae. These relationships suggest that the ordinal and familial classification of Blastoidea are in need of revision. Future research includes placement of Blastoidea in the larger echinoderm framework for the Assembling the Echinoderm Tree of Life project as well as adding taxa to this data set to expand our knowledge of blastoids.