Large worms (>600 mm in length). Deep red in colour. Prostomium bilobed. Five antennae arranged in a slight half-circle; antennae reaching beyond the edge of prostomium. No peristomial cirri. Branchiae present; formed filaments branching from a common area; extending from Ch to Ch?, depending on size.
If older taxonomic literature is used to identify this species, it will key out as M. sanguinea. However, recent work using molecular methods have shown that there are at least three species of Marphysa in the Atlantic formerly called M. sanguinea. It is likely therefore that the species found in the Ranong area may be a new species.
This worm is commonly used as bait by local fishermen.