Scientists have identified a new species of worms, Spartobranchus tenuis, from the Cambrian period. The strange, phallus-like creature is believed to be the 'missing-link' between two groups of modern animals: enteropneusts and pterobranchs. The study was published in the journal Nature.
The new species was about as long as an earthworm and consisted of three segments: a phallus-shaped head, a collar-like structure, and a long tale with gill slits. The tale ended in a bulbous structure the scientists suspect helped the animal anchor in the sea floor. The animal closely resembles modern acorn worms. It lived over 500 million years ago, during the Cambrian explosion, when all modern classifications of animals came into being.
Spartobranchus tenuis differed from acorn worms in that it lived in fibrous tubes, making it similar to pterobranchs, which are colonial animals who live in tubes and feed using tentacles. This similarity suggests that Spartobranchus tenuis could be a common ancestor of enteropneusts and pterobranchs.