CLASSIFICATION OF HETERONEREIS
PHYLUM :- ANNELIDA (Metamerically segmented, coelomate and laterally symmetrical. )
CLASS :- POLYCHAETA (Many setae, clitellum absent. )
ORDER :- ERRANTIA (Free-swimming or burrowing, pharynx protrusible, provided with jaws and teeth. )
GENUS :- Heteronereis
It has cosmopolitan distribution found along the North Atlantic coast, Pacific coast, u.S.A. and Europe.
HABIT AND HABITAT
Heteronereis is a free-swimming worm found in sea.
GENERAL CHARACTERSTICS OF HETERONEREIS
- Malmsgren identified that Heteronereis is the sexual phase of Nereis in which marked modifications occur in the posterior segments of the body which contain gonads.
- During breeding season, clam worm leaves its tube and becomes free-swimming.
- Body is differentiated into asexual anterior atoke and a posterior sexual epitoke which contains gametes.
- Epitoke or posterior part becomes IP0rphoiogically modified as the parapodia for become swimming.
- Parapodia of Heteronereis contain additional foliaceous lobes and setae become oar-like. The notopodium and neuropodium become large leaf-like and act as fins and gills.
- Peristomial cirri become large. Special sensory papillae develop on anal segment.
- Prostomium contains prostomial tentacle, prostomial ocelli and prostomial palp. Peristomium contains peristomial tentacles.
- Muscles and alimentary canal are reduced or become degenerated due to large development of gonads.
- There is no marked sexual dimorphism in both sexes but the females tend to become orange or reddish.
Heteronereis has swarming habit. They swim to the surface of the sea water to shed the sperm or ova. Swarming occurs in the night and in some species they perform nuptial dance. Heteronereis dies after spawning. The development includes trochophore larva which metamorphoses into the adult.
The animal has epitoke, atoke and all above features and hence, it is Heteronereis.