Vetulicolia

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{{deuterostomia}}
{{deuterostomia}}
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In 2001, Shu ''et al.'' suggested that a small group of Cambrian animals which they named '''Vetulicolia''' represented the stem group of modern [[deuterostome]]s. '''Vetulicolia''' possess a distinctly bipartite body plan with a voluminous anterior section bearing five pairs of lateral openings (interpreted as gills) and a seven-segmented "tail". The gut runs to the posterior end of the tail. The junction between the two sections is constricted in the genera ''Xidazoon'' and ''Didazoon'', which have an oval-shaped anterior bearing a large mouth with a strengthened rim, and a leaf-shaped tail. The genus ''Vetulicola'' has a more rectangular anterior with a "carapace" of four rigid cuticular plates. The posterior section is slender, strongly cuticularised and placed dorsally. The whole animal bears a superficial resemblance to a [[Phyllocarida|phyllocarid]] [[Crustacea|crustacean]] which lead to ''Vetulicola'' being originally regarded as an arthropod. However, the complete lack of appendages, the gill openings and the four-plated nature of the carapace are distinct from all known arthropods. Finally, the genus ''Pomatrum'' has an anterior like ''Didazoon'' and'' Xidazoon'', but a slender tail like ''Vetulicola''.  
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In 2001, Shu ''et al.'' suggested that a small group of Cambrian animals which they named '''Vetulicolia''' ("The ancient dwellers") represented the stem group of modern [[deuterostome]]s. '''Vetulicolia''' possess a distinctly bipartite body plan with a voluminous anterior section bearing five pairs of lateral openings (interpreted as gills) and a seven-segmented "tail". The gut runs to the posterior end of the tail. The junction between the two sections is constricted in the genera ''Xidazoon'' and ''Didazoon'', which have an oval-shaped anterior bearing a large mouth with a strengthened rim, and a leaf-shaped tail. The genus ''Vetulicola'' has a more rectangular anterior with a "carapace" of four rigid cuticular plates. The posterior section is slender, strongly cuticularised and placed dorsally. The whole animal bears a superficial resemblance to a [[Phyllocarida|phyllocarid]] [[Crustacea|crustacean]] which lead to ''Vetulicola'' being originally regarded as an arthropod. However, the complete lack of appendages, the gill openings and the four-plated nature of the carapace are distinct from all known arthropods. Finally, the genus ''Pomatrum'' has an anterior like ''Didazoon'' and'' Xidazoon'', but a slender tail shaped superficially like ''Vetulicola'''s (though it moves side to side like other members of Didazoonidae).  
The position of vetulicolians relative to other deuterostomes is still contentious. Shu ''et al.'' did not identify anything resembling a [[notochord]], which may indicate a position outside the deuterostome crown. However, they identified a dark ventral structure in the anterior part of ''Xidazoon'' and ''Didazoon'' as a possible [[endostyle]], a structure currently known only from chordates. Vetulicolians bear a superficial resemblance to a tunicate "tadpole" larva, and also to the divided somato-visceral animal hypothesized by Romer as the ancestor of vertebrates. Shu ''et al.'' (2001).  Lacalli (2002) suggested that the vetulicolian [[cuticle]] was homologous to the urochordate tunic.
The position of vetulicolians relative to other deuterostomes is still contentious. Shu ''et al.'' did not identify anything resembling a [[notochord]], which may indicate a position outside the deuterostome crown. However, they identified a dark ventral structure in the anterior part of ''Xidazoon'' and ''Didazoon'' as a possible [[endostyle]], a structure currently known only from chordates. Vetulicolians bear a superficial resemblance to a tunicate "tadpole" larva, and also to the divided somato-visceral animal hypothesized by Romer as the ancestor of vertebrates. Shu ''et al.'' (2001).  Lacalli (2002) suggested that the vetulicolian [[cuticle]] was homologous to the urochordate tunic.

Revision as of 05:09, 3 February 2009

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