Journal
PROCEEDINGS OF THE ROYAL SOCIETY B-BIOLOGICAL SCIENCES
Volume 287, Issue 1933, Pages -Publisher
ROYAL SOC
DOI: 10.1098/rspb.2020.1467
Keywords
cambrian; orthothecid; soft anatomy; shell microstructure
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Funding
- National Key Research and Development Program [2017YFC0603101]
- Natural Science Foundation of China [41621003, 41890840, 41930319, 41772011]
- Strategic Priority Research Program of Chinese Academy of Sciences [XDB26000000]
- 111 Project [D17013]
- Swedish Research Council [VR2016-04610]
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Hyoliths (hyolithids and orthothecids) were one of the most successful early biomineralizing lophotrochozoans and were a key component of the Cambrian evolutionary fauna. However, the morphology, skeletogenesis and anatomy of earliest members of this enigmatic clade, as well as its relationship with other lophotrochozoan phyla remain contentious. Here, we present a new orthothecid,Longxiantheca miragen. et sp. nov. preserved as part of secondarily phosphatized small shelly fossil assemblage from the lower Cambrian Xinji Formation of North China.Longxiantheca miraretains some ancestral traits of the clade with an undifferentiated disc-shaped operculum, a simple conical conch with apical septa and a two-layered microstructure of aragonitic fibrous bundles. The operculum interior exhibits impressions of soft tissues, including muscle attachment scars, mantle epithelial cells and a central kidney-shaped platform interpreted as a support structure in association with its presumptive feeding apparatus. The muscular system in orthothecids appears to be similar to that in hyolithids, suggesting a consistent anatomical configuration among the total group of hyoliths. The new finding of shell secreting cells demonstrates a mantle regulating the mode of growth for the operculum. Investigations of shell microstructures support the placement of hyoliths as total group molluscs with an unsettled position within the phylum Mollusca.
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