The Burgess Shale

Oikozetetes seilacheri

A possible slug-like animal only known from two different types of shells

Oikozetetes seilacheri (USNM 276247a) – Holotype (left); (GSC 110395) – Paratype (right). Morphs A and B respectively, represented at opposite ends of a presumed slug-like animal. Morph A length = 2.5 mm, Morph B length = 3.5 mm. Specimen dry – direct light. Walcott Quarry.



Kingdom: Animalia
Phylum: Mollusca
Class: Unranked clade halwaxiids (stem group molluscs)

Oikozetetes is thought to represent a halkieriid (Conway Morris, 1995). These organisms are generally considered to be related to the molluscs, although they may fall deeper in the lophotrochozoan stem (Conway Morris and Caron, 2007).

Species name: Oikozetetes seilacheri
Described by: Conway Morris
Description date: 1995

Oikozetetes – from the Greek oikos, “home,” and the Latin zetetes, “quest,” referring to the challenge of classifying the fossils in their correct taxonomic “home.”

seilacheri – after the German paleontologist Adolf Seilacher.

Type Specimens: Holotype – UNSM 276247a in the National Museum of Natural History, Smithsonian Institution, Washington, DC, USA.
Other species:

Burgess Shale and vicinity: none

Other deposits: One unnamed species has been reported from the Lower Cambrian Mernmerna Formation, Flinders Ranges, South Australia (Paterson et al., 2009).

Age & Localities:

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

The Walcott Quarry on Fossil Ridge.

History of Research:

Brief history of research:

No research has been performed on the Burgess Shale Oikozetetes since its initial description by Conway Morris in 1995. Conway Morris noted the similarity of the shells to those of the recently-discovered Halkieria (Conway Morris and Peel, 1990, 1995), and proposed that the two distinct shell forms both belonged to a single animal. Since then, three Oikozetetes-like shells have been found alongside mineralized Halkieria-type sclerites in Australian sediments (Paterson et al., 2009).



All that is known of Oikozetetes is its two mineralized shells (morphs A and B), which typically grow to about 6 mm. The shells are thought to have sat at either end of a slug-like animal similar to Halkieria. This organism may have been covered in Wiwaxia-like sclerites, or may have simply had a tough skin that is never preserved. The frontal shell (morph A) resembles a scallop, with concentric ridges probably representing growth lines surrounding its posterior point; larger flanges form an arrowhead pointing towards the rear of the organism. The rear shell (morph B) is steeply arched and D-shaped, again bearing concentric ridges.


Oikozetetes is rare and is often misidentified in the collections as fragments of the animal Scenella. Conway Morris’s (1995) description included 29 specimens.

Maximum Size:
10 mm


Life habits: Epibenthic, Mobile
Feeding strategies: Herbivorous
Ecological Interpretations:

As with other Burgess Shale slug-like forms, Oikozetetes probably fed on the cyanobacterial Morania mats that grew on the Cambrian sea floor (Caron et al., 2006).


CARON, J.-B., A. H. SCHELTEMA, C. SCHANDER AND D. RUDKIN. 2006. A soft-bodied mollusc with radula from the Middle Cambrian Burgess Shale. Nature, 442: 159-163.

CONWAY MORRIS, S. 1995. Enigmatic shells, possibly halkieriid, from the Middle Cambrian Burgess Shale, British Columbia. Neues Jahrbuch für Geologie und Palaeontologie. Abhandlungen, 195: 319-331.

CONWAY MORRIS, S. AND J. S. PEEL. 1990. Articulated halkieriids from the Lower Cambrian of north Greenland. Nature, 345: 802-805.

CONWAY MORRIS, S. AND J. S. PEEL. 1995. Articulated halkieriids from the Lower Cambrian of North Greenland and their role in early protostome evolution. Philosophical Transactions of the Royal Society of London Series B, 347: 305-358.

PATERSON, J. R., G. A. BROCK AND C. B. SKOVSTED. 2009. Oikozetetes from the early Cambrian of South Australia: implications for halkieriid affinities and functional morphology. Lethaia, 42: 199-203.

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