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An early Cambrian ecdysozoan with a terminal mouth but no anus

By Yunhuan Liu, Huaqiao Zhang, Shuhai Xiao, Tiequan Shao, Baichuan Duan

Posted 06 Sep 2020
bioRxiv DOI: 10.1101/2020.09.04.283960

The ecdysozoans are the most diverse animal group on Earth[1][1], [2][2]. Molecular clock studies indicate that the ecdysozoans may have diverged and diversified in the Ediacaran Period[3][3], [4][4], but unambiguous ecdysozoan fossils first appear in the earliest Cambrian and are limited to cycloneuralians[5][5]–[7][6]. Here we report new material of the early Cambrian microscopic animal Saccorhytus coronarius , which was previously interpreted as a deuterostome[8][7]. Saccorhytus coronarius is reconstructed as a millimetric and ellipsoidal meiobenthic animal with a spinose armor and an anterior mouth but no anus. Purported pharyngeal gills in support of the deuterostome hypothesis[8][7] are shown to be taphonomic artifacts. Phylogenetic analyses indicate that Saccorhytus coronarius belongs to the total-group Ecdysozoa, highlighting the morphological and ecological diversity of early Cambrian ecdysozoans. ### Competing Interest Statement The authors have declared no competing interest. [1]: #ref-1 [2]: #ref-2 [3]: #ref-3 [4]: #ref-4 [5]: #ref-5 [6]: #ref-7 [7]: #ref-8

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