Aysheaia
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Aysheaia Temporal range: Middle Cambrian |
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| Aysheaeia, type specimen, retouched image from Walcott 1911. | |
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| Reconstruction of A. pedunculata | |
| Scientific classification | |
| Kingdom: | Animalia |
| Phylum: | Lobopodia |
| Class: | Xenusia |
| Family: | Aysheaiidae |
| Genus: | Aysheaia |
| Type species | |
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Aysheaia pedunculata Walcott 1911 |
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| Species | |
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Aysheaia was a genus of Cambrian-aged soft-bodied, caterpillar-shaped fossil organisms with average body lengths of 1–6 cm.
Aysheaia has ten body segments, each of which has a pair of spiked, annulated legs. The animal is segmented, and looks somewhat like a bloated caterpillar with a few spines added on — including six finger-like projections around the mouth and two grasping legs on the "head." Each leg has a subterminal row of about six curved claws. No jaw apparatus is evident. A pair of legs marks the posterior end of the body, unlike in onychophorans where the anus projects posteriad; this may be an adaptation to the terrestrial habit.
Based on its association with sponge remains, it is believed that Aysheaia was a sponge grazer and may have protected itself from predators by seeking refuge within sponge colonies. Aysheaia probably used its claws to cling to sponges.
A terminal mouth is also seen in tardigrades that are omnivores or predators (but not detritovores or algavores) — this may provide an ecological signal.
Unlike many early Cambrian forms whose relationships are obscure and puzzling, Aysheaia is remarkably similar to a modern phylum, the Onychophora (velvet worms). Notable differences are the lack of jaws and antennae, and the terminal mouth.
Species of Aysheaia are known from fossils found in the middle Cambrian Burgess shale of British Columbia, and from the Wheeler Formation in Utah. Similar taxa are known from the lower Cambrian Maotianshan shales of China. Other than the 20 specimens from the Greater Phyllopod bed, where they comprise 2% of the community, only 19 specimens of A. pedunculata are known. A. prolata is the species from the similarly-aged Wheeler Shale Formation of Utah.
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