Nereis (also called Neanthes) is a marine worm belonging to Phylum Annelida, Class Polychaeta. Commonly known as the ragworm or clam worm, Nereis is a free-living (errant) polychaete found in marine and brackish environments worldwide. It is a classic example studied in school and college biology for the features of Phylum Annelida.
Nereis: Phylum Annelida, Class Polychaeta (many setae)
Common name: Ragworm or Clam worm
Parapodia on each segment — used for locomotion and respiration
Eversible pharynx with chitinous jaws
Eucoelomate (true coelom)
Closed circulatory system
Polychaeta = many setae; Oligochaeta = few setae (earthworm); Hirudinea = no setae (leech)
Kingdom: Animalia Phylum: Annelida (segmented worms) Class: Polychaeta (many setae) Order: Phyllodocida Genus: Nereis (also known as Neanthes) Common name: Ragworm / Clam worm
Why Polychaeta? Nereis belongs to Class Polychaeta because it has many (poly) setae (chaetae = bristles/hair-like appendages) on each body segment. This contrasts with Oligochaeta (earthworm — few setae) and Hirudinea (leech — no setae).
Body plan: Elongated, flattened, bilaterally symmetrical, segmented (annulated) body.
Segments: The body is divided into many similar segments (metameres). Each segment is separated by septa internally.
Head (Prostomium and Peristomium):
Parapodia: Each body segment (except the first and last) has a pair of paddle-like lateral appendages called parapodia. These are used for locomotion and respiration (gaseous exchange).
Setae: Each parapodium bears numerous setae (bristles made of chitin).
Coelom: True coelom (eucoelomate) — a fluid-filled body cavity lined by mesoderm.
Closed circulatory system: Blood vessels with haemoglobin-like respiratory pigment (erythrocruorin).
Sexes: Separate (dioecious); reproduction involves spawning.
Nereis is used as the standard example of Phylum Annelida in NCERT and other biology textbooks because it shows all the key features of annelids:
Other Annelida examples:
Nereis (also called Neanthes) is a marine worm belonging to Phylum Annelida, Class Polychaeta. Commonly known as the ragworm or clam worm, it is found in marine and brackish environments. It is used as the classic example of polychaetes in biology textbooks.
Nereis belongs to Phylum Annelida and Class Polychaeta. 'Poly' = many, 'chaeta' = setae (bristles). Nereis has many setae on parapodia on each body segment, distinguishing it from Oligochaeta (few setae, e.g., earthworm) and Hirudinea (no setae, e.g., leech).
Parapodia are paired, fleshy, paddle-like lateral appendages present on each body segment of Nereis (except first and last). They bear setae and are used for locomotion (crawling and swimming) and respiration (gaseous exchange, acting as gills). Parapodia are characteristic of Class Polychaeta.
All three belong to Phylum Annelida but different classes: Nereis = Polychaeta (many setae, parapodia, marine). Earthworm = Oligochaeta (few setae, no parapodia, terrestrial). Leech = Hirudinea (no setae, suckers, freshwater/terrestrial). Nereis has the most complex head with eyes and jaws.
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