Priapulus caudatus known as the cactus worm, is a marine invertebrate belonging to the phylum Priapulida.

Priapulids were abundant and widespread in the Early Cambrian period and their tunnelling activities in soft sediment created many trace fossils.

The body is divided into two distinct regions; at the front is the introvert, ridged longitudinally and heavily armed with rows of spines.

The introvert is retractable into the trunk, a longer and broader region with transverse, ring-like markings.

[7] It is believed to be carnivorous while other closely related species are thought to be deposit feeders and detritivores.