Nereis is classified under Phylum Annelida. It is a unisexual annelid and its reproductive phase is called Heteronereis. It is usually called clam worm or sand worm or rag worm which is found on the sea shore in the tubular burrows. Except the peristomium (first segment) and last anal segment, each segment bears laterally one pair of fleshy projections, the para podia, used in swimming.