Quick notes on “Phylogenomic Analyses of Echinodermata Support the Sister Groups of Asterozoa and Echinozoa” (Reich 2015)

Echinodermata is formed by five classes:

  • Crinoidea (feather stars)
  • Asteroidea (sea stars)
  • Ophiuroidea (brittle stars)
  • Holothuroidea (sea cucumbers)
  • Echinoidea (sea urchins and sand dollars)

It is clear that Holothuroidea and Echinoidea form a clade, Echinozoa, but four hypotheses for its relationships with the other classes compete. The predominant ones are the Asterozoan and the Cryptosyringid hypotheses:

  • Asterozoan hypothesis, according to which Asteroidea and Ophiuroidea would form a clade, Asterozoa, which would be sister to Echinozoa.
  • Cryptosyringind hypothesis, according to which Echinozoa form a clade with Ophiuroidea, Cryptosyringida, which then forms a clade with Asteroidea.

Two other hypotheses are based in mitochondrial gene alignments:

  • (Echinozoa + Asteroidea) + Ophiuroidea, with basal Crinoidea
  • (Echinozoa + Asteroidea) + Crinoidea, with basal Ophiuroidea

With 23 de novo sequenced transcriptomes from all five clades of echinoderms, and “multiple phylogenetic methods at a variety of sampling depths”, the “well-supported phylogenetic tree” of this work support the Asterozoan hypothesis.

Picture summary (adapted from the publication):

Reich 2015 edited




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