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Introvert and pharynx of Mafangscolex, a Cambrian palaeoscolecid
Geological Magazine ( IF 2.0 ) Pub Date : 2020-04-21 , DOI: 10.1017/s0016756820000308 Jie Yang , Martin R Smith , Xi-guang Zhang , Xiao-yu Yang
Geological Magazine ( IF 2.0 ) Pub Date : 2020-04-21 , DOI: 10.1017/s0016756820000308 Jie Yang , Martin R Smith , Xi-guang Zhang , Xiao-yu Yang
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.
更新日期：2020-04-21
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