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Animal EvolutionInterrelationships of the Living Phyla$
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Claus Nielsen

Print publication date: 2011

Print ISBN-13: 9780199606023

Published to Oxford Scholarship Online: December 2013

DOI: 10.1093/acprof:oso/9780199606023.001.0001

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Phylum Echinodermata

Phylum Echinodermata

(p.321) 58 Phylum Echinodermata
Animal Evolution

Claus Nielsen

Oxford University Press

The Echinodermata, one of the most well-defined phyla in the animal kingdom, is comprised of approximately 6,600 living species and a very extensive fossil record numbering about 13,000 species. There are five classes: Asteroidea, Ophiuroidea, Echinoidea, Holothuroidea, and Crinoidea. The echinoderms are known for their pentameric body plan, although some echinoids and holothurians show bilaterality, and some asteriods possess more arms. The life cycle of the echinoderms appears to be ancestral. Studies on morphology, fossils, and molecules suggest that the living forms represent two clades, Pelmatozoa and Eleuterozoa. The origin of the echinoderms remains a mystery.

Keywords:   echinoderms, Echinodermata, Asteroidea, Ophiuroidea, Echinoidea, Holothuroidea, Crinoidea, echinoids, Pelmatozoa, Eleuterozoa

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