Ursactis
Extinct genus of annelids
From Wikipedia, the free encyclopedia
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]
| Ursactis Temporal range: | |
|---|---|
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Scientific classification  | |
| 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 | |
Description
Ursactis is a small species, 3–15 millimetres (0.1–0.6 in) long, bearing 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]
