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Worthenella cambria

An enigmatic millipede-like arthropod

Worthenella cambria (USNM 57643) – Holotype, part and counterpart. Left, plate 22 of Walcott (1911), showing a retouched image of the original specimen described (figure 2) together with other “worms.” Right, images of the same specimen. Specimen length = 60 mm. Specimen wet – direct light (left column), dry – polarized light (right column). Walcott Quarry.

© SMITHSONIAN INSTITUTION – NATIONAL MUSEUM OF NATURAL HISTORY. PHOTOS: JEAN-BERNARD CARON

Taxonomy:

Kingdom: Animalia
Phylum: Arthropoda
Higher Taxonomic assignment: Class Megacheira (Hou & Bergström 1997).
Species name: Worthenella cambria
Remarks:

Worthenella has long remained problematic (Briggs & Conway Morris 1986). Legg (2013) proposed that it was a multisegmented “great-appendage” arthropod and formally included it within Megacheira. However, the taxon has remained marginal to recent discussions on early arthropod evolution and phylogenetic analyses, probably because the unique specimen is challenging to interpret and does not provide definitive evidence of its affinity.

Described by: Walcott
Description date: 1911
Etymology:

Worthenella – Possibly after the American palaeontologist Amos Henry Worthen, who died in 1888, just as Walcott’s career was taking off.

cambria – from the Welsh Cambria meaning Wales, in reference to the age of the fossil.

Type Specimens: Holotype –USNM57643 in the National Museum of Natural History, Smithsonian Institution, Washington, DC, USA.
Other species:

Burgess Shale and vicinity: none

Other deposits: none

Age & Localities:

Age:
Middle Cambrian, Wuliuan stage, Burgess Shale Formation (approximately 505 million years ago).
Principal localities:

The Walcott Quarry on Fossil Ridge.

History of Research:

Brief history of research:

Worthenella was first described by Walcott from a single specimen in a 1911 monograph dealing with various Burgess Shale worms. Walcott interpreted this animal as a polychaete annelid (or bristle worm), in the same family as the animal Wiwaxia (which is now interpreted as a stem mollusc). However, This interpretation was questioned (Conway Morris, 1979), and the affinities of Worthenella have remained difficult to establish because this singular fossil is too poorly known (Briggs and Conway Morris, 1986). In light of comparisons with other known Cambrian taxa, Legg (2013) included Worthenella in the class Megacheira, positing the existence of a pair of “great appendages” at the front of the animal.

Description:

Morphology:

The animal is very elongate and tubular, bearing a small head and at least 46 segments of similar size, possibly biramous. Longer appendages are present under the head shield, but their precise nature and arrangement is difficult to determine. The gut is straight and the anus is terminal.

Abundance:

This animal is known from a single specimen.

Maximum Size:
6 cm.

Ecology:

Life habits: Mobile, Benthic
Feeding strategies: Unknown
Ecological Interpretations:

This arthropod was likely eating small organic particles or preying on minute prey items on the sea floor. The lack of detailed information on appendage morphology precludes further ecological interpretations.

References:

  • BRIGGS, D. E. G. and CONWAY MORRIS, S. 1986. Problematica from the Middle Cambrian Burgess Shale of British Columbia. In HOFFMAN, A. and NITECKI, M. H. (eds.) Problematic Fossil Taxa (Oxford Monographs on Geology and Geophysics N° 5), Oxford University Press & Clarendon Press, New York, 167–183 pp.
  • CARON, J. B. and JACKSON, D. A. 2008. Paleoecology of the Greater Phyllopod Bed community, Burgess Shale. Palaeogeography, Palaeoclimatology, Palaeoecology, 258, 222–256.
  • HOU, X. G. and BERGSTRÖM, J. 1997. Arthropods of the Lower Cambrian Chengjiang fauna, southwest China. Fossils and Strata, 45, 1–116.
  • LEGG, D. 2013. Multi-segmented arthropods from the Middle Cambrian of British Columbia (Canada). JOURNAL OF PALEONTOLOGY, 87, 493–501.
  • VANNIER, J. and CHEN, J. 2005. Early Cambrian food chain: New evidence from fossil aggregates in the Maotianshan Shale biota, SW China. PALAIOS, 20, 3–26.
  • WALCOTT, C. 1911. Cambrian Geology and Paleontology II. Middle Cambrian annelids. Smithsonian Miscellaneous Collections, 57(5), 109–145.
  • WILLIAMS, M., SIVETER, D. J., POPOV, L. E. and VANNIER, J. M. C. 2007. Biogeography and affinities of the bradoriid arthropods: Cosmopolitan microbenthos of the Cambrian seas. Palaeogeography, Palaeoclimatology, Palaeoecology, 248, 202–232.
Other Links:

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