NEREIS

Contents hide

CLASSIFICATION OF NEREIS

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 :- Nereis (Rag worm or Clam worm)

It has cosmopolitan distribution found along the North Atlantic coast, Pacific coast, u.S.A. and Europe.

Nereis is a marine crawling type, living in temporary burrows in sand, 200 meters deep. They are free-living, predaceous, nocturnal, carnivorous, often found buried in the intertidal sad.

Commonly called as Rag worm or Clam worm and is the simplest annelid.
Examination of preserved specimen shows cylindrical and elongated body form which is divided into similar metameres or segments about 200 in number.
First few segments fuse to form head which is composed of (i) prostomium or preoral lobe, which carries prostomial tentacles, palps and ocelli; and (ii) peristomium (2 segments fused), which carries antero-laterally 4 pairs of peristomial tentacles.
Mouth is found on the anterior surface of the peristomium.
Body segments, except head and anal segment, contain each pair of locomotory parapodia.
Segments are also called as metameres and between two segments in intersegmental groove.
Parapodia also serve as respiratory and circulatory organs. Each parapodium is composed of dorsal notopodium and ventral neuropodium. Parapodium also possesses aciculum for support and needle like setae for crawling.
Anal segment contains a pair or anal cirri.
Nereis is dioecious, although male and female worms can hardly be recognized.