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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 Sipuncul

Phylum Sipuncul

(p.134) 26 Phylum Sipuncul
Animal Evolution

Claus Nielsen

Oxford University Press

The phylum Sipuncula is comprised of approximately 150 benthic, marine species. Fossils from the Lower Cambrian suggest a number of strikingly ‘modern’ sipunculans. The sipunculans have two body cavities containing various types of coelomocytes: a small, anterior tentacle coelom; and a large, posterior body coelom. The body coelom has a pair of large metanephridia, with the nephridiopores situated near the anus. Most species have lecithotrophic trochophores that swim with the cilia of the prototroch protruding through pores in the egg envelope. Sipunculus has a special pericalymma larva with the prototrochal epithelium extended posteriorly, covering mouth and hyposphere. The Sipuncula has an apparently unquestioned monophyly and is generally placed together with the Annelida, although the former may be treated as a separate phylum to facilitate comparisons with the annelids.

Keywords:   sipunculans, Sipuncula, body cavities, trochophores, cilia, Sipunculus, monophyly, Annelida, annelids, coelomocytes

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