I am not entirely sure this is a Peanut worm but I cannot find anything else close.
From benthic grab
t rex found! for sale $100000000000
Specimen #: BBEL_0104, Collection Event #: BLIZ_005, Common Name: peanut worm, Magnification: .67x, Notes: send to Mary Rice for identification, Location: Smithsonian Institution's Field Station on Carrie Bow Cay, Belize
Collected from one cubic foot of backreef substrate plus water in the lagoon behind Carrie Bow Cay. CBCUBE_03_BCBC_402_DSC_8365.jpg
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.