''Phragmochaeta canicularis'' is an extinct animal belonging to the annelids and lived in the Early Cambrian (

Atdabanian Cambrian Stage 3 is the still unnamed third stage of the Cambrian. It succeeds Cambrian Stage 2 and precedes Cambrian Stage 4, although neither its base nor top have been formally defined. The plan is for its lower boundary to correspond approxim ...

in the local timescale, about 520 million years ago).''Phragmochaeta canicularis''
at

Fossilworks Fossilworks is a portal which provides query, download, and analysis tools to facilitate access to the Paleobiology Database The Paleobiology Database is an online resource for information on the distribution and classification of fossil animals ...

.org Fossils have only been found in the Buen Formation at the Sirius Passet

Lagerstätte A Lagerstätte (, from ''Lager'' 'storage, lair' '' Stätte'' 'place'; plural ''Lagerstätten'') is a sedimentary deposit that exhibits extraordinary fossils with exceptional preservation—sometimes including preserved soft tissues. These for ...

, Greenland and the animal is probably the first polychaete.

Etymology

The genus name ''Phragmochaeta'' references the thatch−like appearance of the chaetae, hence reeds (Greek: ''phragmites'').Conway Morris & Peel, 2008, p.144 The species

epithet An epithet (, ), also byname, is a descriptive term (word or phrase) known for accompanying or occurring in place of a name and having entered common usage. It has various shades of meaning when applied to seemingly real or fictitious people, di ...

''canicularis'' is derived from the Latin for "dog" (''canis'') in reference to Sirius ("dog-star") Passet.Conway Morris & Peel, 2008, p.145

Description

Drawing from roughly 40 fossils ''Phragmochaeta'' consisted of about twenty segments, each of which carried structures typical of the annelids polychaetes (notochaetae and neurochetae). The notochaetae seemed to cover the entire dorsal surface, while the neurochaetae projected obliquely along the axis of the body. The head is not well known, but it seems there was no type of jaw. The intestine was unbent and has large longitudinal musculature.

Lifestyle

It probably was a

benthic The benthic zone is the ecological region at the lowest level of a body of water such as an ocean, lake, or stream, including the sediment surface and some sub-surface layers. The name comes from ancient Greek, βένθος (bénthos), meaning "t ...

animal, which lived on the bottom of the sea and probably ate particles present on the seabed. This animal moved thanks to the neurochete, while the dorsal notochets provided protection.

Classification

This animal belonged to the annelates polychaetes, a group of animals currently represented by numerous marine species. Already in the middle Cambrian of Burgess Shales they were present with numerous species (''

Burgessochaeta ''Burgessochaeta'' is an extinct genus of polychaete annelids from the Middle Cambrian. Its fossils have been found in the Burgess Shale in British Columbia, Canada. A total of 189 specimens of ''Burgessochaeta'' are known from the Greater Phyll ...

'', '' Canadia'', '' Peronochaeta''), but Phragmochaeta, antecedent of some millions of years, represents the oldest polychaete and was probably one of the most primitive.

Importance

''Polychaetes'' are rare in the Maotianshan Shales, in China, also dating back to the lower Cambrian. This is particularly surprising because the Chinese field has a very wide biological variety. The only Cambrian field containing polychaetes is that of Burgess Shale, in Canada, a little later. ''Phragmochaeta'', therefore, represents an exception as the oldest known polychaete.

References

Bibliography

* {{Taxonbar, from=Q3901706 Polychaetes Cambrian invertebrates Cambrian animals of North America Cambrian Greenland Fossils of Greenland Buen Formation Fossil taxa described in 2008 Cambrian genus extinctions