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Burgessochaeta setigera

A burrowing bristleworm with a pair of long tentacles

Image of Burgessochaeta setigera.

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Burgessochaeta setigera (ROM 61042) – Part and counterpart. Complete specimen showing gut contents and fecal material expelled from the anus (black strand visible on the counterpart, right images). Specimen length = 26 mm. Specimen wet – direct light (top row), wet – polarized light (bottom row). Walcott Quarry.

© Royal Ontario Museum. Photos: Jean-Bernard Caron

Media 1 of 2 for Burgessochaeta setigera Photo
Media 2 of 2 for Burgessochaeta setigera Photo

Taxonomy

Kingdom:

Animalia

Phylum:

Annelida

Class:

Unranked clade (stem group polychaetes)

Affinity:

Burgessochaeta bears some resemblance to modern polychaetes but it cannot be placed in any extant group (Conway Morris, 1979; Eibye-Jacobsen, 2004) suggesting a position as a stem-group polychaete (Budd and Jensen, 2000).

Species name:

Burgessochaeta setigera

Described by:

Walcott

Description date:

1911

Etymology:

Burgessochaeta – from Mount Burgess (2,599 m), a mountain peak in Yoho National Park. Mount Burgess was named in 1886 by Otto Klotz, the Dominion topographical surveyor, after Alexander Burgess, a former Deputy Minister of the Department of the Interior. Also from the Latin chaeta, “bristle”, a common suffix for polychaete worms, reflecting spiny structures along their body.

setigera – from the Latin saetula, “small bristle.”

Type Specimens:

Lectotype –USNM57650 in the National Museum of Natural History, Smithsonian Institution, Washington, DC, USA.

Other species:

Burgess Shale and vicinity: none.

Other deposits: none.

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Age

Period:

Middle Cambrian, Bathyuriscus-Elrathina Zone (approximately 505 million years ago).

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Localities

Principal localities:

The Walcott Quarry on Fossil Ridge.

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History of Research

Brief history of research:

First reported by Charles Walcott in 1911 and lumped into the genus Canadia (Walcott, 1911), Burgessochaeta was formally described as a separate genus by Simon Conway Morris in his 1979 treatise on the polychaetes of the Burgess Shale. Because it is rather common, Burgessochaeta has proven useful in calculating the extent of decay in fossil assemblages (Caron and Jackson, 2006).

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Description

Morphology:

This slender worm reached lengths of 1.8-4.9 cm (2.9 cm on average). Its width was constant (around 2 mm), except towards either end, where it tapered off. Its head bore a pair of long, smooth tentacles that reached 6 mm in length. The variation in shape seen among these tentacles suggests that the organism could contract and extend them. Its first segment also bears uniramous parapodia (paired single-branch appendages), while those of the other two dozen are biramous (divided into two). All of its body segments are similar to one another. Its parapodia bear in the range of 11-17 simple setae (usually 15), each about 2 mm in length, and which form a single plane that is inclined steeply with respect to the body. The tips of these setae form unequal forks, with one prong about half the length of the other. The animal had an unarmed eversible proboscis (prominent flexible apparatus capable of being turned inside-out like a tongue) that formed the front portion of its straight gut.

Abundance:

Burgessochaeta is relatively common in the Walcott Quarry representing 0.4% of the specimens counted in the community (Caron and Jackson, 2008).

Maximum size:

49 mm

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Ecology

Life habits:

Epibenthic, endobenthic, mobile

Feeding strategies:

Deposit feeder

Ecological Interpretations:

Burgessochaeta probably burrowed or moved along the surface of the mud, using its short parapodia. Its tentacles are thought to have been used to collect food; the presence of sediment in its gut suggests that it might have been a deposit feeder.

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References

Bibliography:

BUDD, G. E. AND S. JENSEN. 2000. A critical reappraisal of the fossil record of the bilaterian phyla. Biological Reviews, 75: 253-295.

CARON, J.-B. AND D. A. JACKSON. 2006. Taphonomy of the Greater Phyllopod Bed Community, Burgess Shale. PALAIOS, 21: 451-465.

CARON, J.-B. AND D. A. JACKSON. 2008. Paleoecology of the Greater Phyllopod Bed community, Burgess Shale. Palaeogeography, Palaeoclimatology, Palaeoecology, 258: 222-256.

CONWAY MORRIS, S. 1979. Middle Cambrian polychaetes from the Burgess Shale of British Columbia. Philosophical Transactions of the Royal Society of London. Series B, Biological Sciences, 285(1007): 227-274.

EIBYE-JACOBSEN, D. 2004. A reevaluation of Wiwaxia and the polychaetes of the Burgess Shale. Lethaia, 37: 317-335.

WALCOTT, C. D. 1911. Middle Cambrian annelids. Smithsonian Miscellaneous Collections, 57(2): 109-144.

Other links:

None

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