Nereis mainly parasitizes on the shell of oyster and does not corrode the inside of oyster. Nereis is non-toxic and harmless, belonging to normal parasitic marine worms. Nereis is common in intertidal zone and also in deep sea. Nereis is the dominant invertebrate under rocks, cracks, algae, coral reefs or soft sediments. They mainly eat other worms and small marine animals. Except for a few species such as Nereis japonica, which live in fresh water or brackish water and have little morphological change before reproduction, most species of Nereistidae have obvious morphological change before reproduction, which is called Heteronereis.
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