A phylum of worm-like animals, the priapulids are also known as the ‘penis worms’ due to their shape. Priapulids are known from fossils as early as the Cambrian Period (e.g. Ottoia from the Burgess Shale) and are represented by about 20 extant species. They live in burrows in soft sediment and have an invertible proboscis – their mouth parts turn inside out to feed.