Amiskwia is a large Cambrian gnathiferan with complex gnathostomulid-like jaws

Abstract

Phylogenomic studies have greatly improved our understanding of the animal tree of life but the relationships of many clades remain ambiguous. Here we show that the rare soft-bodied animal Amiskwia from the Cambrian of Canada and China, which has variously been considered a chaetognath, a nemertine, allied to molluscs, or a problematica, is related to gnathiferans. New specimens from the Burgess Shale (British Columbia, Canada) preserve a complex pharyngeal jaw apparatus composed of a pair of elements with teeth most similar to gnathostomulids. Amiskwia demonstrates that primitive spiralians were large and unsegmented, had a coelom, and were probably active nekto-benthic scavengers or predators. Secondary simplification and miniaturisation events likely occurred in response to shifting ecologies and adaptations to specialised planktonic habitats.

Jean-Bernard Caron and Brittany Cheung provide new evidence that the rare Cambrian animal Amiskwia is closely related to gnathiferans, thereby resolving its ambiguous phylogeny. They describe new specimens from the Burgess Shale that preserve the complex jaw apparatus, which is most similar to gnathostomulids.