Reconstruction of Aysheaia pedunculata.
© Marianne Collins
Aysheaia is one of a variety of lobopodian taxa from the Cambrian, which are early members of the lineage that gave rise to arthropods, and whose only modern survivors are onychophorans (velvet worms) and tardigrades (water bears). Lobopodians characteristically have annulated, unjointed bodies and bear soft limbs after which they are called: the lobopods. Although the finding is not consensual, the type of claws and orientation of rear limbs suggest that Aysheaia could be the earliest member of the water bear lineage.
Genus – after the nearby Aysha peak (since renamed Ayesha peak) in the Wapta icefield (3,065 m); original meaning unknown.
species – from the Latin pedunculus, “foot.”
Burgess Shale and vicinity: none
Other deposits: A.? prolata from the Middle Cambrian of Utah (Robison, 1985).
The Walcott Quarry on Fossil Ridge.
Walcott originally described Aysheaia as an annelid worm (Walcott 1911). It was later re-described as a velvet worm (or a close relative) (Brues 1923; Walton 1927; Hutchinson 1930; Walcott 1931), although it lacked features such as jaws and slime glands. Certain authors advocated a position in its own phylum (Tiegs & Manton 1958). A morphological reinterpretation based on photographs (Delle Cave & Simonetta 1975) prompted a detailed re-study of the fossil specimens (Whittington 1978), and relationships were suggested with the water bears (tardigrades) (Bergström 1978). Although some more recent phylogenetic approaches resolve Aysheaia as a basal lobopodian (Smith & Ortega-Hernandez 2014; Yang et al. 2015), other find support for a more derived affinity and a close relationship with tardigrades (Caron & Aria 2017, 2020).
Aysheaia is a worm-like animal, 1 to 6 cm in length and about 5 mm broad, bearing ten pairs of clawed, spiny limbs on the lower part of its body. It did not have a separate head, but a mouth occupied the very front of the body, accompanied by a pair of appendages and a circlet of bumps (papillae). The animal had a soft, flexible, non-mineralized cuticle, which had a corrugated, accordion-like form. Each stubby limb had ten corrugations, some of which bore a spiny projection. The terminal pair of limbs was oriented towards the front of the animal. A suite of claws also adorned the end of each stub-foot. A faint line running down the axis of the organism is interpreted as its gut.
Aysheaia is rare in the Walcott Quarry representing less than 0.04% of the specimens counted in the community (Caron and Jackson, 2008).
Aysheaia is frequently associated with the remains of sponges, and an ecological association has been posited. Considering recent evidence that other lobopodians lived anchored to a substrate for suspension-feeding (Caron & Aria 2017), it is possible that Aysheaia also used sponges as substrate for its lifestyle, although the animal lacked the morphological specializations of a suspension feeder, and more likely grazed or predated walking on their surface.