New observations on the palaeoscolecid worm Tylotites petiolaris from the Cambrian Chengjiang Lagerstatte, south China

概要

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The Lower Cambrian Chengjiang Lagerstatte provides a remarkable window to enable investigation of the early diversification of introvert worms. Tylotites petiolaris Luo and Hu, 1999 is a very rare animal of the fauna originally regarded as a kind of lobopodian based on an incomplete specimen, but its affinities to recent phyla are still controversial. New materials of the taxon collected in recent years confirm that it is most closely related to the palaeoscolecidians with which it shares features such as a proboscis consisting of a slightly swollen introvert bearing many scalids, a collar (buccal cone) and a spinose pharynx. Both possess a smooth neck as a median zone between the introvert and the trunk, a pair of terminal hooks and a trunk bearing transverse ridges intercalated with furrows. Therefore, a new order Cricocosmida of the class Palaeoscolecida is erected herein based on these shared characters. The trunk spines of T. petiolaris are somewhat dorso-ventrally differentiated indicating an epifaunal life on the sea floor. Numerous fine transverse wrinkles possibly beneath the uppermost cuticle of the ventral trunk of the animal are tentatively interpreted as the circular muscles, a feature crucial to understanding the problematic systematic position of the palaeoscolecidians.
日本古生物学会の論文
2007-04-30