Document Detail

Machaeridians are Palaeozoic armoured annelids.
MedLine Citation:
PMID:  18185586     Owner:  NLM     Status:  MEDLINE    
The systematic affinities of several Palaeozoic skeletal taxa were only resolved when their soft-tissue morphology was revealed by the discovery of exceptionally preserved specimens. The conodonts provide a classic example, their tooth-like elements having been assigned to various invertebrate and vertebrate groups for more than 125 years until the discovery of their soft tissues revealed them to be crown-group vertebrates. Machaeridians, which are virtually ubiquitous as shell plates in benthic marine shelly assemblages ranging from Early Ordovician (Late Tremadoc) to Carboniferous, have proved no less enigmatic. The Machaeridia comprise three distinct families of worm-like animals, united by the possession of a dorsal skeleton of calcite plates that is rarely found articulated. Since they were first described 150 years ago machaeridians have been allied with barnacles, echinoderms, molluscs or annelids. Here we describe a new machaeridian with preserved soft parts, including parapodia and chaetae, from the Upper Tremadoc of Morocco, demonstrating the annelid affinity of the group. This discovery shows that a lineage of annelids evolved a dorsal skeleton of calcareous plates early in their history; it also resolves the affinities of a group of problematic Palaeozoic invertebrates previously known only from isolated elements and occasional skeletal assemblages.
Jakob Vinther; Peter Van Roy; Derek E G Briggs
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Publication Detail:
Type:  Historical Article; Journal Article    
Journal Detail:
Title:  Nature     Volume:  451     ISSN:  1476-4687     ISO Abbreviation:  Nature     Publication Date:  2008 Jan 
Date Detail:
Created Date:  2008-01-10     Completed Date:  2008-02-05     Revised Date:  -    
Medline Journal Info:
Nlm Unique ID:  0410462     Medline TA:  Nature     Country:  England    
Other Details:
Languages:  eng     Pagination:  185-8     Citation Subset:  IM    
Department of Geology and Geophysics, Yale University, PO Box 208109, New Haven, Connecticut 06520, USA.
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MeSH Terms
Annelida / anatomy & histology,  classification*,  ultrastructure
History, Ancient
Comment In:
Nature. 2008 Jan 10;451(7175):133-4   [PMID:  18185574 ]

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