Shankouclava Explained

Shankouclava is an extinct genus of tunicates. It represents the oldest candidate member of this group, dating to . It has been found in the Lower Cambrian Maotianshan Shale at Shankou village, Anning, near Kunming (South China). Each of the eight specimens found and used for description were isolated, suggesting that the genus was solitary and not colonial.^[1]

Morphology

Shankouclava had a soft, sac-like body that was elongated and pointed proximally. The body lengths of individuals vary from 2 cm (0.8 in) to 4 cm (1.6 in).

Degan Shu asserts that some fossil specimens exhibit tentacles, which would make the genus similar to the deuterostome Phlogites.^[2] Expanding on this idea, Shu and colleagues argue against a tunicate affinity for Shankouclava.^[3]

Etymology

The generic name is composed of the fossil locality, Shankou, and the Latin word clava (club-shaped).

Classification

A stem group tunicate affinity for Shankouclava has been broadly accepted, though some authors have expressed reservations that the evidence in favour of this affinity is not conclusive.^[4]

Another Cambrian tunicate, Megasiphon, known from a single specimen, resembles more closely the morphology of surviving tunicates.^[5]

Notes and References

1. Chen, Jun-Yuan . Huang, Di-Ying . Peng, Qing-Qing . Chi, Hui-Mei . Wang, Xiu-Qiang . Feng, Man . 2003 . The first tunicate from the Early Cambrian of South China . Proceedings of the National Academy of Sciences . 100 . 12835415 . 14 . 8314–8318 . 166226 . 10.1073/pnas.1431177100 . 2003PNAS..100.8314C . free .
2. Shu . Cambrian explosion: Birth of tree of animals . 2008 . Gondwana Research. 14 . 1–2 . 219–240 . 10.1016/j.gr.2007.08.004 . 2008GondR..14..219S .
3. 10.1098/rspb.2009.0646. The earliest history of the deuterostomes: The importance of the Chengjiang Fossil-Lagerstätte. 2010. Shu. D.-G.. Conway Morris. S.. Zhang. Z.-F.. Han. J.. Proceedings of the Royal Society B: Biological Sciences. 277. 1679. 165–174. 19439437. 2842668.
4. Conway Morris. 10.1098/rstb.2006.1846 . 16754615 . Darwin's dilemma: the realities of the Cambrian 'explosion'. Philos Trans R Soc Lond B Biol Sci. 29 June 2006 . 361. 1470. 1069–1083 . 1578734 .
5. 10.1038/s41467-023-39012-4. A mid-Cambrian tunicate and the deep origin of the ascidiacean body plan. 2023. Nanglu. Karma. Lerosey-Aubril. Rudy. Weaver. James C.. Ortega-Hernández. Javier. Nature Communications. 14. 1. 3832. 37414759. 10325964.