Spartobranchus

Spartobranchus is an extinct genus of acorn worm from the Cambrian Burgess Shale. It contains the species Spartobranchus tenuis. It is similar to the modern representatives of the family Harrimaniidae, although distinguished by living in branching fibrous tubes. It is a likely stem-member of the acorn worms, although it is somewhat intermediate between them and pterobranchs. Studies show that the ability to create tubes were lost in the line leading to modern acorn worm, but remained in the pterobranchs. However recently Antarctic torquatorids have been found that also make tubes.