Opabinia
| Opabinia Temporal range: Early Cambrian
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Fossil
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| Genus: | Opabinia
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| Species: | O. regalis
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| Binomial name | |
| Opabinia regalis | |
Opabinia regalis is a curious animal found in early Cambrian fossil deposits. It is known from only two fossil beds -- the Middle Cambrian Burgess Shale of British Columbia and the Lower Cambrian Maotianshan shales of Yunnan, China. Its discoverer, Charles Walcott, named it after a local mountain, Opabin.
The animal was segmented and had a soft-shelled exoskeleton. The head carried an array of five, apparently functional, eyes and a long, flexible, hose-like proboscis or snout which appears to be in no way homologous to the head appendages of any other known contemporary lifeform. At the end of the proboscis were grasping spines; these are theorised to have served as a grab to catch prey.
The body segments each featured a set of gills and a pair of flap-like appendages that are also dissimilar to other known animals of the time. The three rearmost flaps formed the tail. Unlike known arthropods, the head does not appear to be formed from fused segments. The animal was covered with what appears to be a soft, flexible shell with no joints between the segments. Opabinia has no known relatives except possibly Anomalocaris.
Opabinia is thought to have lived in the soft sediment on the seabed, although it presumably could have swum after prey using its side lobes. On the bottom, the proboscis could have plunged into sand burrows after worms. It could also have been used to rapidly stir up sea floor sediment in search of food. If this were the case, Opabinia would then have folded back the proboscis to bring the food to its mouth on the underside of its head.
Although Opabinia is a relatively minor constituent of the early faunas, it has historical significance because it was one of the first truly unusual animals to be completely studied and described during the redescription of the Burgess shale faunas in the 1970s. Harry Blackmore Whittington showed convincingly in 1975 that the animal, previously thought to be an arthropod, was indeed not an arthropod, and moreover, that it was unlikely it belonged to any other known phylum. Taken with two other unexpectedly unique arthropods, Marella and Yohoia, both of which had been previously described, Opabinia has demonstrated that the softbodied Burgess faunas were much more complex and diverse than anyone had previously suspected.