© Royal Ontario Museum. Photos: Jean-Bernard Caron
Fieldia belongs to the priapulid worm stem group (Harvey et al., 2010; Wills, 1998).
Fieldia – from Field, the mountain peak (2,643 m) and small town near Fossil Ridge, British Columbia, Canada. The name was given by William Cornelius Van Horne (General Manager of the Canadian Pacific Railway), to honour Cyrus West Field, a promoter of the first telegraph cable across the Atlantic Ocean.
lanceolata – from the Latin lanceolatus, “lance-shaped,” in reference to the shape of the worm.
Burgess Shale and vicinity: none.
Other deposits: none.
The Walcott Quarry on Fossil Ridge.
Walcott (1912) was the first to describe Fieldia, which he mistook for the carapace of a crustacean. He later classified a different specimen with the priapulid Ancalagon (known then as “Ottoia minor” Walcott, 1931). Conway Morris (1977) re-described the genus as a primitive priapulid worm based on new material he had found in the Smithsonian’s collections; later studies showed that it belonged to the priapulid stem group (Harvey et al., 2010; Wills, 1998).
Fieldia is a cylindrical worm about five centimeters in length, with a spine-covered body (trunk) and a rather small, eversible mouthpart, called a proboscis. The proboscis is lined with small spines at the front and several rows of hooks posteriorly. It is not known if the proboscis could be fully retracted or inverted as in other fossil and Recent priapulid worms. The gut is often preserved with a mud infill, and runs along the centre of the body. The trunk does not have annulations and is divided into an anterior, middle and a posterior part. The mud infill is most conspicuous in the middle part of the trunk.
This species is very rare. Only a single specimen was originally described by Walcott (1912) and about a dozen specimens were studied by Conway Morris (1977).
Fieldia is commonly preserved with mud inside its gut, suggesting that it fed directly on the sea-floor sediments. Its tubular body-shape is well adapted for burrowing; it probably used its spines to pull itself through the mud.
CONWAY MORRIS, S. 1977. Fossil priapulid worms. Special Papers in Palaeontology, 20: 1-95.
HARVEY, T. H. P., X. DONG AND P. C. J. DONOGHUE. 2010. Are palaeoscolecids ancestral ecdysozoans? Evolution & Development, 12(2): 177-200.
WALCOTT, C. 1912. Cambrian Geology and Paleontology II. Middle Cambrian Branchiopoda, Malacostraca, Trilobita and Merostomata. Smithsonian Miscellaneous Collections, 57(6): 145-228.
WALCOTT, C. 1931. Addenda to descriptions of Burgess Shale fossils. Smithsonian Miscellaneous Collections, 85(3): 1-46.
WILLS, M. A. 1998. Cambrian and Recent disparity: the picture from priapulids. Paleobiology, 24(2): 177-199.