Halwaxiids and the early evolution of the lophotrochozoans

Science

Volumn 315, Issue 5816, 2007, Pages 1255-1258

  Morris, Simon Conway ^a   Caron, Jean Bernard ^b  

^a UNIVERSITY OF CAMBRIDGE   (United Kingdom)

^b DEPARTMENT OF NATURAL HISTORY   (Canada)

Author keywords

[No Author keywords available]

Indexed keywords

SCLERITE; UNCLASSIFIED DRUG;

EVOLUTION; FOSSIL; LARVA; LIFE HISTORY; METAZOAN; PHYLOGENETICS; SCLERITE;

ARTICLE; EVOLUTION; FOSSIL; HALWAXIID; LOPHOTROCHOZOA; LOWER CAMBRIAN; METAZOON; MIDDLE CAMBRIAN; MONOPHYLY; NONHUMAN; PHYLOGENY; PRIORITY JOURNAL; TAXONOMY;

ANIMALS; ANNELIDA; EVOLUTION; FOSSILS; INVERTEBRATES; MOLLUSCA; PHYLOGENY;

LOPHOTROCHOZOA; METAZOA;

EID: 33847630385     PISSN: 00368075     EISSN: 10959203     Source Type: Journal    
DOI: 10.1126/science.1137187     Document Type: Article

References (30)

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18. Systematic section is as follows: Superphylum Lophotrochozoa. Stem-group Halwaxida, defined as cataphract metazoans with three principal zones of sclerites and usually at least one shell. Component genera include Australohalkieria, Drepanochites, Eohalobia, Halkieria, Lomasulcachites, Ninella, Ocruranus, Oikozetetes, Orthrozanclus, Sinosachites, Siphogonuchites (Lopachites and Maikhanella may be junior synonyms), Thambetolepis, ana Wiwaxia. This list is likely to be incomplete and possibly also includes synonyms, not in the least because most taxa are only known from disarticulated material. Family Orthrozanclidae Conway Morris and Caron fam. nov. Component genus is Orthrozanclus and possibly Oikozetetes. Genus Orthrozanclus Conway Morris and Caron gen. nov. Orthrozanclus reburrus sp. nov. Etymology: Generic name is compound, based on sickle-like (Greek zanclon) sclerites and oblique reference to ancestral nature (Greek arthros, or "dawn"); specific name refers to hairy (Latin reburrus) appearance. Holotype: Royal Ontario Museum (ROM) 57197. Other material: ROM 57833 to 57840, National Museum of Natural History (USNM) 21369S and 213696. Stratigraphy and locality: Burgess Shale Formation, Walcott Quarry Member, Middle Cambrian. All specimens are from the Greater Phyllopod Bed, Fossil Ridge, near Mount Field, British Columbia, Canada (17). Diagnosis: Cataphract metazoan, scleritome of individual sclerites, and at least one shell. Sclerites form at least three zones: small dorsal sclerites, prominent dorso-lateral spines, and lateral (cultrate), including elongate, anterior spines. Anterior shell convex, anterior umbo, arched posterior margin, ventrally anterior doublure.
19. Sclerites show similar preservation to co-occurring wiwaxiids, which are known to be unmineralized and probably were originally chitinous (12). The shell shows prominent relief and clear growth lines and was almost certainly composed of calcium carbonate, although it is now demineralized.
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30. We thank V. Brown for technical support in Cambridge; D. Evans, C. Schander, A. Scheltema, and D. Zanatta for assistance and comments on the cladistic analysis; M. Collins for drafting the reconstruction; and three anonymous referees for constructive criticism. This work is supported by the Royal Society, Cowper-Reed Fund, St. John's College, Parks Canada, and the Royal Ontario Museum, Collections were made under the direction of D. Collins. This is Royal Ontario Museum Burgess Shale Research Project #10.