Earthworm-like protrusions on oyster shells are not parasites. Earthworm-like protrusions on oyster shells are Nereis or Nereis, which are common in shellfish shells and rarely parasitic in oysters. Nereis and Nereis can also eat by themselves. The live Nereis on the oyster shell indicates that the oyster is fresh.

Nereis, also known as "sea earthworm", often adheres to the surface of oyster shells. Some sea worms on oysters are difficult to clean, and will be embedded in the seams along the lace of oyster shells, so it is difficult for high-pressure pumps to wash them down. Earthworms are edible, non-toxic and high in protein, and are also rare bait for sea fishing.