Looks a lot like Phascolosoma agassizii. Found under a rock in sandy substrate.
Strange looking worm found on the beach just above the tide
This is the first time I've found Phascolosoma agassizii, or Agassiz's Peanut Worm. It was found under a rock at low tide, and measured between 2 and 3" long, about as wide as a pencil.
Worm-like thing sticking out of a hole in the rock. It withdrew when I disturbed it.
The Sipuncula or Sipunculida (common names sipunculid worms or peanut worms) is a group containing 144-320 species (estimates vary) of bilaterally symmetrical, unsegmented marine worms. Traditionally considered a phylum, they might be a subgroup of phylum Annelida based on recent molecular work.