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.
HABIT AND HABITAT
- 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.
GENERAL CHARACTERSTICS OF NEREIS
- 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.
The animal has prostomium, peristomium, parapodium and all above features and hence it is Nereis.