Habitat

The Priapulida is a phylum of marine worms found in seas and oceans around the World. Their fossil record goes back over 500 million years to the Cambrian and the fossil genus Ottoia is one of the largest and most abundant worms found in the Burgess Shale assemblage. Priapulus caudatus is one of about 20 species of extant priapulid worms and is widely distributed around the northern hemisphere from the Arctic to the Mediterranean and from Alaska to California in the eastern Pacific Ocean. The animals grow up to 15 cm long and are common in coastal waters living in soft mud to a depth of at least 300m.

Biology

The priapulids have a cylindrical body with external annulations and an internal hydrostatic skeleton - the body cavity is large and fluid filled. The mouth is anterior and found at the end of a introvert, ringed by spines, that can be extended from the front of the body for feeding. The alimentary canal is straight and the anus is terminal. Priapulus caudatus has a prominent feathery structure at the posterior of the body which is likely to be used for gas exchange. It is a detritivore when small and becomes an active predator as it becomes larger: in captivity, in the absence of alternative food, they will happily eat each other.

Priapulus caudatus has separate sexes although some other priapulid species are hermaphroditic. Embryonic development is only recently becoming properly understood with few studies published over the past century. The females produce tens of thousands of tiny eggs, fertilisation is external and development is direct via an embryo with holoblastic radial cleavage and a larva with a cuticular casing called a lorica. Their cuticle is periodically moulted throughout the life of the animal as they grow larger.

The priapulids are a member of the major group of animal phyla called the Ecdysozoa along with other animals that moult their cuticles (Ecdysis) including the arthropods and nematodes. Their precise relationships to the other ecdysozoan phyla is uncertain but their closest relatives are likely to be the minute marine phyla the Loricifera and Kinorohyncha.

Sequencing Plan

Survey sequencing of the Priapulus caudatus genome is currently underway to gather information needed to prepare a sequencing plan.

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Contacts

Name	Affiliation
John Spieth	The Genome Institute, Washington University School of Medicine
Max Telford	University College London
Graham Budd	Uppsala Universitet
David Ferrier	University of St Andrews

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