Reconstruction of Habelia optata.
© Marianne Collins
Habelia optata is an arthropod, but its exact relationships remain poorly understood. It has been aligned in some studies to the arachnomorphs (a group including chelicerates and trilobites), and has either been allied with lamellipedians such as Naraoia and the trilobites (Briggs and Fortey, 1989), or placed within Megacheira as closely related to Leanchoilia (Wills et al., 1998).
Habelia – from Mount Habel (3,161 m), today known as Mount Des Poilus, at the head of Yoho Valley. Named in 1900 by Norman Collie in honour of Jean Habel, a German mountaineer. The name Mount Habel is now applied to a peak north of Mount Des Poilus.
optata – unspecified; may derive from the Latin optatus, “wish or desire.”
Burgess Shale and vicinity: Habelia? brevicauda from Walcott Quarry and Raymond Quarry, Fossil Ridge.
Other deposits: none.
The Walcott and Raymond Quarries on Fossil Ridge.
Habelia optata was first described by Walcott in 1912, and a possible second species Habelia? brevicauda was added to the genus by Simonetta in 1964. Habelia was later restudied by Whittington (1981). Habelia has been included in some phylogenetic analyses of arthropod relationships (Briggs and Fortey, 1989; Wills et al., 1998) and unusual zig-zag fossil tracks from the Middle Cambrian of the Grand Canyon have been ascribed to an arthropod similar to Habelia (Elliott and Martin, 1987).
Habelia optata is unusual in that its entire body is covered in tubercles (small, rounded nodules) that are particularly dense on the head shield and the axis of the body trunk. Its body consists of a convex head shield without eyes, and twelve body tergites with a long, jointed posterior spine projecting from the twelfth segment. The first three tergites have a thick median spine that bore tubercles. The head has a pair of multi-segmented setose antennae at the front, and two pairs of possibly biramous appendages with segmented walking limbs and dark sheets that may be filamentous branches.
The twelve body segments have a thick, blunt median spine on the dorsal surface. The first six body segments have appendages that are segmented and branch into two (biramous), including long stout segmented gnathobasic walking limbs (i.e., with a robust and spiny basal podomere or segment used for crushing food items) and a lobed outer branch with lamellae (small elongated structures) along the margin. The lobes are also present on the posterior segments, but no walking branches are associated with them. The tail is a long spine with a single joint midway along its length.
Extremely rare
Habelia optata probably used its six trunk limbs for walking, reserving the head appendages for manipulating food items. It is likely that the frontal antennae were used to sense the environment since there are no obvious eyes. The size and shape of the posterior margin of the head suggests that there was considerable flexure possible between the head and the body, indicating that Habelia may have dug in the sediment for food items. It lived on the muddy seafloor and was heavily protected against predators by its thick body armor and pointed posterior spine, the latter of which would make it difficult for predators to attack from behind.
BRIGGS, D. E. G. AND R. A. FORTEY. 1989. The early radiation and relationships of the major arthropod groups. Science, 246: 241-243.
ELLIOTT, D. K. AND D. L. MARTIN. 1987. A new trace fossil from the Cambrian Bright Angel Shale, Grand Canyon, Arizona. Journal of Paleontology, 61: 641-648.
SIMONETTA, A. M. 1964. Osservazioni sugli artropodi non trilobiti della ‘Burgess Shale’ (Cambriano medio). III conributo. Monitore Zoologico Italiano, 72: 215-231.
WALCOTT, C. D. 1912. Middle Cambrian Branchiopoda, Malacostraca, Trilobita and Merostomata. Smithsonian Miscellaneous Collections, 57: 145-228.
WILLS, M. A., D. E. G. BRIGGS, R. A. FORTEY, M. WILKINSON AND P. H. A. SNEATH. 1998. An arthropod phylogeny based on fossil and recent taxa, p. 33-105. In G. D. Edgecombe (ed.), Arthropod fossils and phylogeny. Columbia University Press, New York.
WHITTINGTON, H. B. 1981. Rare arthropods from the Burgess Shale, Middle Cambrian, British Columbia. Philosophical Transactions of the Royal Society of London Series B-Biological Sciences, 292: 329-357.
None
