Saccoglossus

Saccoglossus is a genus of acorn worm. It is the largest genus in the Enteropneusta class, with 20 species.

This genus is characterized especially by the concentric rings of muscle fibers in the proboscis. Many Saccoglossus can be found in coastal mud and sand habitat, often near bays. They dig tubes in the substrate, ejecting conical piles of castings in a spiral fashion.