Ursactis

Ursactis Temporal range: Wuliuan PreꞒ Ꞓ O S D C P T J K Pg N ↓
Scientific classification
Domain:	Eukaryota
Kingdom:	Animalia
Phylum:	Annelida
Class:	Polychaeta
Order:	incertae sedis
Genus:	†Ursactis Osawa, Caron & Gaines, 2023
Species:	†U. comosa
Binomial name
†Ursactis comosa Osawa, Caron & Gaines, 2023

Ursactis is an extinct genus of Cambrian polychaete annelid.[1] It was found in the Wuliuan Stage of the Burgess Shale, although most specimens come from a Burgess Shale locality known as the Tokumm Creek in northern Kootenay National Park.[1] Ursactis is the most abundant Cambrian polychaete found as of 2023.[1]

Description

Ursactis is small species, 3–15 millimetres (0.1–0.6 in) long, with a pair of large palps. It has between 8 and 10 segments, a smaller number than other polychaetes.[1] Because specimens with 10 segments vary in size significantly and the length of each segment increases with the body length, researchers think Ursactis grew its segments rather adding new ones.[1] Meanwhile, modern polychaetes add new segments throughout their life. This suggests that annelids began to start adding new segments during their life by the mid-Cambrian.[1]

See also

• 2023 in paleontology

References

1. Osawa, Hatena; Caron, Jean-Bernard; Gaines, Robert R. (2023). "First record of growth patterns in a Cambrian annelid". Royal Society Open Science. 10 (4): 221400. Bibcode:2023RSOS...1021400O. doi:10.1098/rsos.221400. ISSN 2054-5703. PMC 10130728. PMID 37122950.