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Article: Lophotrochozoa in the Cambrian evolutionary radiation and the Pelagiella problem

Papers in Palaeontology - Volume 7 Issue 1 - Cover
Publication: Palaeontology
Volume: 7
Part: 4
Publication Date: November 2021
Page(s): 2227 2244
Author(s): Ed Landing, Gerd Geyer, Igor A. Jirkov, and Stefano Schiaparelli
DOI: 10.1002/spp2.1396
Addition Information

How to Cite

LANDING, E., GEYER, G., JIRKOV, I.A., SCHIAPARELLI, S. 2021. . Papers in Palaeontology, 7, 4, 2227-2244. DOI: /doi/10.1002/spp2.1396

Author Information

  • Ed Landing - New York State Museum 222 Madison Avenue Albany NY 12230 USA
  • Gerd Geyer - Institut für Geographie und Geologie Bayerische Julius-Maximilians-Universität Am Hubland 97074 Würzburg Germany
  • Igor A. Jirkov - Department of General Ecology & Hydrobiology Biological Faculty Moscow State University Leninskiye Gory, 1, Building 12 Moscow 119234 Russia
  • Stefano Schiaparelli - Dipartimento di Scienze terra dell’Ambiente e della Vita (DISTAV) Università di Genova C.so Europa 26 16132 Genova Italy
  • Stefano Schiaparelli - Museo Nazionale dell’Antartide (MNA, Sede di Genova) Viale Benedetto XV 5 16132 Genova Italy

Publication History

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    Abstract

    Tiny snail-like conchs of Pelagiella Matthew are important in discussions of lophotrochozoan and mollusc origins in the Cambrian evolutionary radiation (CER). The limited morphological features of Pelagiella conchs have led to the ‘Pelagiella problem’: (1) poorly distinguished Pelagiella species; (2) an exceptional genus range across all Cambrian palaeocontinents and climate belts; (3) an unparalleled genus-lifespan (c. 31 myr) in the early Palaeozoic; and (4) the assumption that all Pelagiella spp. are gastropods, which compromises lophotrochozoan and mollusc phylogenies. The type species P. atlantoides is a gastropod, but we show that so-called Pelagiella species with sub-to-triangular apertures and turbiniform conchs are not referable to the genus. Re-evaluation of spectacular specimens of Pelagiella exigua Resser & Howell show it to be a polychaete with two apertural paleal chaetae fan arrays. Given that some modern sedentary polychaetes have paleal fan arrays, Pexigua is regarded as a likely member of the Sabellida Levinsen and is assigned to Pseudopelagiella gen. nov. Other Pelagiella spp. and forms with similar conchs are probably polychaetes not relevant to syntheses of early mollusc diversification. Pelagiellidae fam. nov. should be restricted to the late early Cambrian (c. 508 Ma) P. atlantoides. Pseudopelagiella exigua was unattached, probably benthic and lived with the apical conch surface on the sea floor, a mode of life similar to that of another family of the Sabellida, the sessile spirorbids that are cemented to substrate. Among numerous crown groups, the late early Cambrian eve of the CER included the polychaete Pseudopelagiella exigua and gastropod P. atlantoides.

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