The Gut Contents of Ottoia (Priapulida) from the Burgess Shale: Implications for the Reconstruction of Cambrian Food Chains  

Ottoia prolifica (Walcott, 1911) is one of the most abundant priapulid worms of the Middle Cambrian Burgess Shale fauna, and often occurs in large numbers on the surface of bedding planes – suggesting gregarious habits.   Its “banana-shaped” body is divided into an anterior introvert (proboscis) armed with longitudinal rows of hook-like scalids and spines, and a posterior annulated trunk bearing terminal hooks.  Some specimens are preserved with the introvert invaginated into the anterior part of the trunk.  Those showing a fully everted introvert display a long, cylindrical pharynx lined with small pharyngeal teeth.  The detailed morphology of the pharyngeal region suggests that Ottoia was a predator that probably used a feeding mechanism comparable with that of large Recent priapulids (e.g. Priapulus) – i.e. seizing prey with the everted pharynx, and drawing it into the gut by inverting the pharynx and retracting the introvert. 

O. prolifica was infaunal, as indicated by individuals preserved within their burrows.  The scalid rows and the trunk hooks are likely to have anchored the body in the surrounding sediment at some points in the burrowing process. 

Preliminary study of abundant material from the Walcott Quarry Shale (Burgess Shale Formation) reveals gut contents in numerous specimens of O. prolifica. Hyolith exoskeletal fragments, such as cones, opercula, and the helens of Halophrentis carinatus, are the most common food remnants preserved in the O. prolifica gut.  Brachiopods (e.g. Micromitra burgessensis), bradoriids (e.g. Liangshanella burgessensis), and small trilobites (agnostid and non-agnostid larval stages) are present at a smaller frequency.   These gut contents bring direct evidence that Ottoia fed on a variety of small, epibenthic, mostly slow-moving prey.  Clusters of unrecognizable microscopic elements, typically concentrated within the posterior part of the gut, suggest that other types of prey were consumed by Ottoia. Appropriate methods (scanning electron microscopy, CT-scan) are expected to reveal their composition.  Elongated masses of very fine black material are also frequent in the posterior gut and may represent digested residues.  These also require detailed morphological and chemical analysis.  Although there is no doubt that O. prolifica was an infaunal worm that lived in burrows and fed at the water-sediment interface, its feeding behaviour – that is, whether or not it was a selective feeder – requires clarification.