Cambrian palaeoscolecidomorph Cricocosmia caught in the act of moulting

ABSTRACT

Molting (ecdysis) is a ubiquitous behaviour and critical process in the growth and development of extant ecdysozoans. The origin of ecdysis can be traced back to the early Cambrian period, primarily in arthropods and priapulid-like worms. However, understanding the molting process in palaeoscolecidomorphs, the most diversified group of Cambrian priapulid-like worms, is challenging owing to the limited number of fossils preserved with molting features. Here, we report abnormal palaeoscolecidomorph Cricocosmia jinningensis (from the early Cambrian Chengjiang Lagerstätte, South China) that is distinguished by conjoined and 3–4 longitudinal rows of sclerites along the trunk, showing pre-molting features. The molting process of C. jinningensis could be reconstructed as follows: the new cuticle initially forms and lies beneath the old one; the new cuticle separates from the old one by dislocating and staggering the sclerites; the new worm frees itself by shedding the old cuticle from the broken anterior body, similar to that observed in living priapulid worms. To our knowledge, this is the first in the act instance of molting behaviour in C. jinningensis. The ecological purpose of molting in adult C. jinningensis may be removal of symbiotic organisms attached to its trunk and replacement of the worn-out sclerites.

KEYWORDS:

• Cricocosmia jinningensis
• ecdysis
• Palaeoscolecidomorpha
• early Cambrian
• Chengjiang Lagerstätte
• ecology

Acknowledgments

We thank J. Luo and M. Cheng (NWU) for their assistance with fossil collection and Q. Zhang (NWU) for assistance with micro-XRF analyses. We also thank the two anonymous reviewers and Dr. Harriet B. Drage for their constructive comments.

Disclosure statement

No potential conflict of interest was reported by the author(s).

Data accessibility

All the specimens used in this study are deposited in the Early Life Institute and Department of Geology (http://geology.nwu.edu.cn/). Correspondence and requests for materials should be addressed to DW ([email protected]).

Additional information

Funding

This study was funded by the National Natural Science Foundation of China [grant numbers 42202009 to DW and 42372012 and 41720104002 to JH], the China Post-doctoral Science Foundation [grant number 2022M722568 to DW], “open for collaboration” grant from Yunnan Key Laboratory for Palaeobiology, Yunnan University (to DW), and the National Key Research and Development Programme of China [grant number 2023YFF0803601 to JH].