Amiskwia sagittiformis

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A worm-like, swimming animal with paired antennae

Reconstruction of Amiskwia sagittiformis.

Amiskwia sagittiformis (USNM 198670) – Paralectotype. Complete specimen showing antennae, fins and gut trace. Specimen length (with tentacles) = 19 mm. Specimen wet – direct light. Walcott Quarry.

Amiskwia sagittiformis (USNM 57644) – Paralectotype. Complete specimen preserved in oblique view showing antennae (one is partially curled), fins and gut trace. Specimen length (with tentacles) = 23 mm. Specimen wet – direct light (left); dry – polarized light (right). Walcott Quarry.

Amiskwia sagittiformis (USNM 57645) – Lectotype. Complete specimen showing antennae, fins and gut trace. Specimen length (with tentacles) = 25 mm. Specimen wet – direct light (left); dry – polarized light (right). Walcott Quarry.

Taxonomy:

Kingdom: Animalia

Phylum: Unknown

Higher Taxonomic assignment: Non applicable

Species name: Amiskwia sagittiformis

Remarks:

The phylogenetic position of Amiskwia is uncertain. Despite significant objections to its traditional interpretation as a chaetognath (Conway Morris, 1977; Owre and Bayer, 1962), some workers still hold this view (Butterfield, 1990). Nemertine (Owre and Bayer, 1962) and molluscan (Chen and Huang, 2002; Chen et al., 2005) affinities have also been suggested, but not substantiated.

Described by: Walcott

Description date: 1911

Etymology:

Amiskwia – from the Cree amiskwi, “beavertail,” a name given to various topographical features in Yoho National Park.

sagittiformis – from the Latin sagitta, “arrow,” and formis, “shape,” in reference to the general outline of the animal.

Type Specimens: Lectotype – UNSM 57644 in the National Museum of Natural History, Smithsonian Institution, Washington, DC, USA.

Other species:

Burgess Shale and vicinity: none.

Other deposits: A. sinica (Chen et al., 2002) from the Lower Cambrian Chengjiang deposits, Yunnan, China.

Age & Localities:

Age:

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:

Described by Walcott in 1911, Amiskwia was originally interpreted as an arrow-worm (Walcott, 1911). Originally popular, this interpretation fell into disrepute after further studies (Conway Morris, 1977; Owre and Bayer, 1962), but it has more recently been reconsidered as a possible arrow-worm (Butterfield, 1990).

Description:

Morphology:

Amiskwia is a symmetrical, flattened worm. It bears a pair of lateral fins in addition to a paddle-like tail fin. A pair of small tentacles is situated on the bottom of its head, just in front of its mouth. The trace of a gut and other internal organs are preserved in the fossils.

Abundance:

A. saggitiformis is known from only a couple dozen specimens from the Walcott Quarry, comprising only 0.025% of the specimens counted (Caron and Jackson, 2008).

Maximum Size:

25 mm

Ecology:

Life habits: Nektonic, Mobile

Feeding strategies: Unknown

Ecological Interpretations:

The presence of fins demonstrates that Amiskwia was well adapted for swimming. Its rarity in the Burgess Shale suggests that it may have spent much of its time well above the sea bed, above the depth at which it could be caught in submarine mudslides.

References:

BUTTERFIELD, N. J. 1990. Organic preservation of non-mineralizing organisms and the Taphonomy of the Burgess Shale. Paleobiology, 16(3): 272-286.

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

CHEN, J.-Y. AND D.-Y. HUANG. 2002. A possible Lower Cambrian chaetognath (arrow worm). Science, 298(5591): 187.

CHEN, J.-Y., D.-Y. HUANG AND D. J. BOTTJER. 2005. An Early Cambrian problematic fossil: Vetustovermis and its possible affinities. Proceedings of the Royal Society B: Biological Sciences, 272(1576): 2003-2007.

CHEN, L., H. LUO, S. HU, J. YIN, Z. JIANG, Z. WU, F. LI AND A. CHEN. 2002. Early Cambrian Chengjiang fauna in Eastern Yunnan, China. Yunnan Science and Technology Press, Kunming, China, 199 p.

CONWAY MORRIS, S. 1977. A redescription of the Middle Cambrian worm Amiskwia sagittiformis Walcott from the Burgess Shale of British Columbia. Palaontologische Zeitschrift, 51(3): 271-287.

OWRE, H. B. AND F. M. BAYER. 1962. The systematic position of the Middle Cambrian fossil Amiskwia Walcott. Journal of Paleontology, 36(6): 1361-1363.

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