Phylum Nematoda

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Nematoda, or roundworms, are a phylum of cylindrical, unsegmented worms with a complete digestive system. They are found in diverse environments and include free-living species as well as parasitic species that infect plants, animals, and humans.

General Characteristics:

1) Habitat: Mostly parasitic (in animals/plants), few free living. 

2) Shape: Body is perfectly cylindrical in shape adapted for living in minute place.

3) Symmetry: They have bilateral symmetry. 

4) Germ Layer: They are Triploblastic animals.

5) Coelom: Body cavity is “Pseudocoel”.

6) Organization: They have the organ system level of organization. 

7) Cuticle: Body wall composed of thick & tough cuticle, epidermis & musculture.

8) Digestion: They have complete digestive system, alimentary canal is distinct with mouth & anus.

9) Reproduction: Reproduce by sexual reproduction. They are sexually dimorphic animals. Fertilization is internal. 

10) Respiration: They respirete through body surface by diffusion.

11) Excretion: Excretion is done by ‘Renette glands’.

12) Nervous system: It consists of a nerve ring and many longitudinal nerve cords.

13) Sense Organ: Sense organ at the anterior end ‘amphid’ and posterior end is ‘phasmid’ present.

14) Sperm cells: They posses amoeboid sperm cell.

Examples: Ascaris lumbricoides (Round worm); Loa loa (Eye worm); Wucheria bancrofti (filarial worm); Rhabditis sp. (free living)

Classes of Nematoda:

There are two class in the phylum Nematoda.

  1. Adenophorea or Aphasmida 
  2. Secernentea or Phasmida

1.) Adenophorea or Aphasmida :

  1.  Habitat: Marine, mostly free living.
  2. Amphid: The members possess variously shaped amphid) (Chemosensory organ) behind the lips. 
  3.  Phasmid: Phasmid (caudally located sensory pits) absent in caudal area. 
  4.  Excretory system: The excretory system consists of Renette cells/gland without lateral canals.
  5. Testis: Generally males has two testis.
  6. Glands: Most of species possess caudal adhesive glands. and epidermal glands.

Example:Trichinella sp. (Trichina worm); Dorylaimus sp.

2.) Secernentea or Phasmida:

  1.  Habitat: Mostly parasitic, freeliving species are largely terrestrial.
  2. Amphid: These species comprises pore like labial amphid in the lateral lips.
  3. Phasmid: In the caudal region there is presence of a pair of phasmids.
  4. Testis: Males with a single testis.
  5. Excretory system: Excretory system canal like and comparatively more complex complex.  
  6.  Glands: Epidermal and caudal adhesive glands are absent.

Example: Ascaris lumbricoides (Round worm). Wucheria bancrofti (Filarial worm)

Phylum Platyhelminthes Phylum Annelida

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