Phragmochaeta canicularis is an extinct animal belonging to the annelids and lived in the Early Cambrian (Atdabanian in the local timescale, about 520 million years ago).

[1] Fossils have only been found in the Buen Formation at the Sirius Passet Lagerstätte, Greenland and the animal is probably the first polychaete.

[3] The species epithet canicularis is derived from the Latin for "dog" (canis) in reference to Sirius ("dog-star") Passet.

[4] Drawing from roughly 40 fossils Phragmochaeta consisted of about twenty segments, each of which carried structures typical of the annelids polychaetes (notochaetae and neurochetae).

Already in the middle Cambrian of Burgess Shales they were present with numerous species (Burgessochaeta, Canadia, Peronochaeta), but Phragmochaeta, antecedent of some millions of years, represents the oldest polychaete and was probably one of the most primitive.