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Introvert and pharynx of Mafangscolex, a Cambrian palaeoscolecid

Published online by Cambridge University Press:  21 April 2020

Jie Yang ,
Martin R Smith Open the ORCID record for Martin R Smith [Opens in a new window] ,
Xi-guang Zhang  and
Xiao-yu Yang Open the ORCID record for Xiao-yu Yang [Opens in a new window]
Jie Yang
Affiliation:
Key Laboratory for Palaeobiology, Yunnan University, Kunming650091, China MEC International Joint Laboratory for Palaeobiology and Palaeoenvironment, Yunnan University, Kunming650091, China
Martin R Smith
Affiliation:
Department of Earth Sciences, Durham University, Durham, DH1 3LE, UK
Xi-guang Zhang
Affiliation:
Key Laboratory for Palaeobiology, Yunnan University, Kunming650091, China MEC International Joint Laboratory for Palaeobiology and Palaeoenvironment, Yunnan University, Kunming650091, China
Xiao-yu Yang*
Affiliation:
Key Laboratory for Palaeobiology, Yunnan University, Kunming650091, China MEC International Joint Laboratory for Palaeobiology and Palaeoenvironment, Yunnan University, Kunming650091, China
*
Author for correspondence: Xiao-yu Yang, Email: xyyang@mail.ynu.edu.cn
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Abstract

Palaeoscolecid worms are widespread in the Palaeozoic period, and are of key importance to understanding the emergence of moulting animals (superphylum Ecdysozoa). However, palaeoscolecids lack a diagnostic set of morphological characters, and as such are unlikely to form a natural (monophyletic) group. Consequently, detailed anatomical study of individual taxa is necessary in order to evaluate the phylogenetic significance of palaeoscolecids. New specimens of Mafangscolex from the Cambrian Stage 3 Xiaoshiba Lagerstätte in Kunming, China, provide the first detailed account of a proboscis in Palaeoscoelcida sensu stricto, a core group of palaeoscolecids characterized by having a tessellating scleritome of phosphatic plates and platelets. The eversible mouthparts of Mafangscolex comprise an armoured, hexaradially symmetrical introvert, a ring of coronal spines and quincuncially arranged pharyngeal armature, with a range of tooth morphologies. Taken together, this configuration strikingly resembles the proboscis arrangement inferred for the ancestral ecdysozoan. The six-fold symmetry represents an important difference from the pentaradial priapulan proboscis. The retention of key aspects of the ancestral ecdysozoan body plan suggests that palaeoscolecids represent a useful window on the earliest stages of ecdysozoan evolution.

Keywords

Palaeoscoelcida sensu strictoproboscisecdysozoan evolutionXiaoshiba LagerstätteCambrian Stage 3
Type
Original Article
Information
Geological Magazine , Volume 157 , Issue 12 , December 2020 , pp. 2044 - 2050
Copyright
© Cambridge University Press 2020

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