3D animation of Yuknessia simplex.
© Phlesch Bubble
Yuknessia consists of the tubes of miniature colonial animals called pterobranchs (Hemichordata). The tubes were formed as clustered colonies, with the tubes themselves possessing the zig-zagging growth marks that are diagnostic of the Pterobranchia.
Yuknessia – from Yukness Mountain (2,847m), a Peak in Yoho National Park, east of the Burgess Shale.
simplex – from the Latin simplex, meaning “simple,” in reference to its simple morphology.
Burgess Shale and vicinity: Yuknessia stephenensis from the Trilobite Beds on Mount Stephen (LoDuca et al. 2015)
Other deposits: Yuknessia stephenensis from the Wheeler Shale (Utah) and Spence Shale (Utah) (Conway Morris and Robison, 1988; LoDuca et al. 2015). Yuknessia sp. from the Lower Cambrian Niutitan Formation in China (Yang et al., 2003).
Burgess Shale and vicinity: The Walcott Quarry on Fossil Ridge and the Trilobite Beds on Mount Stephen.
Other deposits: none
This genus was described by Charles Walcott (1919) as a possible green alga. It was redescribed by LoDuca et al. (2015) as the tubes of a hemichordate.
Yuknessia consists of a colony of branching tubes that were constructed by pterobranch individuals known as zooids. While the zooids themselves are not preserved, the growth mode of the tubes, in particular a series of zig-zagging growth marks known as fuselli, are diagnostic of the hemichordate class Pterobranchia. The tubes are thin, and range from 4mm-13mm, although 6mm is more common.
Yuknessia is very rare and represents only 0.04% of the Walcott Quarry community (Caron and Jackson, 2008).
All pterobranchs, including Yuknessia, were suspension feeders. The zooids possessed tentacle-laden feeding arms which would have extended into the surrounding water. The tentacles would then trap passing food particles and transport them down to the mouth. The actual zooids themselves would have been attached to zooids in adjacent tubes with a system of tissues called the stolon system. In this way, Yuknessia actually represents a colony of related individuals rather than a single animal. The tubes of Yuknessia would have been attached directly to the seafloor or a hard substrate such as a rock or fragments of biomineralizing animals. While the zooids could move up and down within their individual tubes, the colony itself was immobile.
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