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Systematics, phylogeny and historical biogeography of the Pentagonaster clade (Asteroidea : Valvatida : Goniasteridae)
Christopher
Mah
Department of Invertebrate Zoology, National Museum of Natural History, MRC-163, PO Box 37012 Smithsonian Institution, Washington, DC 20560, USA. Email: mahch@si.edu
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Invertebrate Systematics 21(4) 311–339 http://dx.doi.org/10.1071/IS06049
Submitted: 11 November 2006
Accepted: 9 June 2007
Published online: 20 September 2007
Abstract
Morphology-based phylogenetic hypotheses developed for living and fossil goniasterid asteroids have provided several unique opportunities to study bathymetric and biogeographic shifts for an ecologically important group of prominent, megafaunal invertebrates. A cladistic analysis of 18 ingroup taxa employing 65 morphological characters resulted in a single most parsimonious tree. The tree supports assignment of the Atlantic Tosia parva (Perrier, 1881) and the Pacific Tosia queenslandensis Livingstone, 1932 to new, separate genera. The phylogenetic tree supports offshore to onshore bathymetric shifts between basal and derived taxa. The phylogeny is also consistent with historical events surrounding the separation of Antarctica from Australia and South Africa. Buterminaster Blake & Zinsmeister, 1988 from the Eocene La Meseta Formation, Antarctic Peninsula, was included in the phylogenetic analysis and is now supported as the only fossil species in the genus Pentagonaster Gray, 1840. Pentagonaster stibarus H. L. Clark, 1914 is separated from synonymy with P. dubeni Gray, 1847 and resurrected as a valid species. The new genus, Akelbaster, gen. nov., shows unusual new structures that resemble cribiform organs, although their function has not been determined. One specific ingroup lineage, including Tosia and Pentagonaster, attains a much larger adult size than those of its sister-taxa, suggesting that Cope’s rule may apply to asteroids within this clade. Pentagonaster and related genera are revised. Descriptions of four new genera and three new species are presented, including: Akelbaster novaecaledoniae, gen. nov., sp. nov., Ryukuaster onnae, gen. nov., sp. nov., Eknomiaster beccae, sp. nov., Pawsonaster parvus, gen. nov., comb. nov. and Anchitosia queenslandensis, gen. nov., comb. nov.
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