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.