Phylum Nematoda
Definition of Phylum Nematoda:
Phylum Nematoda are un-segmented vermiform animals with anterior lateral chemosensory organs or amphids and with a persistent blastocoel or pseudocoelom; dorsal and ventral nerve cords in epidermis and excretory system of renette cells or tubules.
General Characteristic Features of Phylum Nematoda:
1. Body of Phylum Nematoda is un-segmented, bilaterally symmetrical, elongated and tapering at both ends.
2. Triploblastic animals with perivisceral cavity is more extensive than that of Platyhelminthes.
3. Body of of Phylum Nematoda is generally covered with thick, flexible multi-layered collagenous cuticle and often bears cuticular setae (hairs), spines or annulations.
4. Cuticle moulted periodically.
5. Epidermis or hypodermis syncytial; i.e., the nuclei are not separated from each other by cell membranes.
6. Only longitudinal body-wall muscles; no circular body-wall muscles.
7. Body cavity of of Phylum Nematoda is pseudocoel filled with parenchyma in most cases.
8. Alimentary canal provided with distinct mouth and anus (complete digestive tract). Muscular pharynx and the inner surface of the gut usually not lined by cilia. Extracellular digestion.
9. Mouth of of Phylum Nematoda is surrounded by six lips.
10. Blood vascular system and respiratory system are absent in of Phylum Nematoda.
11. Haemoglobin sometimes present in the pseudocoelomic fluid.
12. Excretory system without nephridia and flame cells. In the class Adenophorea glandular renette cells with a duct or in the class Secernentea excretory canal system without flame cells act as excretory system.
13. Dorsal and ventral nerve cords in the epidermis.
14. Chemosensory organs are small cuticular projections called amphids which are situated on the lips, derived from cilia and opening to the exterior through a small pore, and lined with modified non-motile cilia called sensillae.
15. Sexes of of Phylum Nematoda are separate (gonochoristic).
16. Tubular gonads are present in of Phylum Nematoda.
17. Amoeboid sperm cells.
18. Fertilization is internal in of Phylum Nematoda.
19. Determinate cleavage (mosaic).
20. of Phylum Nematodaare eutelic animals.
21. Generally complex life history.
22. They are free-living or phytoparasitic or zooparasitic.
Classification of Phylum Nematoda:
Following the scheme of Chitwood (1933), the phylum Nematoda is divided into two classes:
1. Adenophorea or Aphasmida and
2. Secernentea or phasmidea.
Class 1. Adenophorea or Aphasmida (Gk. Adenophorea = gland-bearing; Gk. Aphasmida – without phasmids):
1. Most species possess caudal adhesive glands and epidermal glands.
2. Phasmids (caudal papillae bearing pores connecting with glandular pouch called phasmids which are thought to be chemosensory in function) are absent.
3. Amphids are post labial and variously shaped such as pouch-like or tube-like, rarely pore-like.
4. Coelomocytes well developed.
5. Excretory organs are only renette cells but without collecting tubules.
6. Males usually without caudal alae.
7. Usually two testes in males.
8. Mostly marine, and include both free- living and parasitic species. The free- living species include both terrestrial, freshwater, and major marine forms.
The class Adenophorea or Aphasmida contains the following orders:
Order 1. Enoplida:
1. Cuticle provided with bristles.
2. 6 labial papillae and 10-12 sensory bristles are present.
3. Cyanthiform amphids.
4. Mostly marine.
Examples:
Enoplus, Anticoma, Metonchdiamus.
Order 2. Dorylaimida:
1. Cuticle smooth and without bristles.
2. 6-10 labial papillae.
3. Cyanthiform amphids.
4. Buccal cavity with a protrusible spear.
5. Mostly terrestrial.
Examples:
Dorylaimus, Tylencholaimus, Xiphinema, Trichodoris.
Order 3. Mermithida:
1. Cuticle smooth and without bristles.
2. 16 labial papillae.
3. Amphids cyanthiform or reduced.
4. Invertebrate parasites (larval stage); adult stage free-living.
Examples:
Mermis, Agamermis, Paramermis.
Order 4. Chromadorida:
1. Cuticle smooth or ringed with heavy bristles.
2. Spiral amphids.
3. Pharynx with a posterior bulb.
4. Mostly marine and free-living.
Example:
Paracanthonchus, Paracytholaimus.
Order 5. Desmoscolecida:
1. Cuticle heavily ringed with prominent bristles throughout or certain areas of the body.
2. Anterior end with 4 sensory bristles.
3. Amphids crescent-shaped or pump- shaped.
4. Marine and free-living nematodes.
Examples:
Desmoscolex, Greefiella, Epsilonema.
Order 6. Monohysterida:
1. Cuticle smooth or slightly ringed, often with bristles.
2. Anterior end with 4, 6, or 8 bristles or multiple of the above numbers.
3. Amphids circular.
4. Mostly marine, some fresh water and some terrestrial.
Examples:
Monohystera, Saiphonolaimus.
Order 7. Araeolaimida:
1. Cuticle smooth, sometimes with bristles.
2. Labial papillae present.
3. Four cephalic bristles at the anterior end.
4. Amphids spiral.
Examples:
Plectus, Odontophora, Wilsonema.
15. Sexes of of Phylum Nematoda are separate (gonochoristic).
16. Tubular gonads are present in of Phylum Nematoda.
17. Amoeboid sperm cells.
18. Fertilization is internal in of Phylum Nematoda.
19. Determinate cleavage (mosaic).
20. of Phylum Nematodaare eutelic animals.
21. Generally complex life history.
22. They are free-living or phytoparasitic or zooparasitic.
Classification of Phylum Nematoda:
Following the scheme of Chitwood (1933), the phylum Nematoda is divided into two classes:
1. Adenophorea or Aphasmida and
2. Secernentea or phasmidea.
Class 1. Adenophorea or Aphasmida (Gk. Adenophorea = gland-bearing; Gk. Aphasmida – without phasmids):
1. Most species possess caudal adhesive glands and epidermal glands.
2. Phasmids (caudal papillae bearing pores connecting with glandular pouch called phasmids which are thought to be chemosensory in function) are absent.
3. Amphids are post labial and variously shaped such as pouch-like or tube-like, rarely pore-like.
4. Coelomocytes well developed.
5. Excretory organs are only renette cells but without collecting tubules.
6. Males usually without caudal alae.
7. Usually two testes in males.
8. Mostly marine, and include both free- living and parasitic species. The free- living species include both terrestrial, freshwater, and major marine forms.
The class Adenophorea or Aphasmida contains the following orders:
Order 1. Enoplida:
1. Cuticle provided with bristles.
2. 6 labial papillae and 10-12 sensory bristles are present.
3. Cyanthiform amphids.
4. Mostly marine.
Examples:
Enoplus, Anticoma, Metonchdiamus.
Order 2. Dorylaimida:
1. Cuticle smooth and without bristles.
2. 6-10 labial papillae.
3. Cyanthiform amphids.
4. Buccal cavity with a protrusible spear.
5. Mostly terrestrial.
Examples:
Dorylaimus, Tylencholaimus, Xiphinema, Trichodoris.
Order 3. Mermithida:
1. Cuticle smooth and without bristles.
2. 16 labial papillae.
3. Amphids cyanthiform or reduced.
4. Invertebrate parasites (larval stage); adult stage free-living.
Examples:
Mermis, Agamermis, Paramermis.
Order 4. Chromadorida:
1. Cuticle smooth or ringed with heavy bristles.
2. Spiral amphids.
3. Pharynx with a posterior bulb.
4. Mostly marine and free-living.
Example:
Paracanthonchus, Paracytholaimus.
Order 5. Desmoscolecida:
1. Cuticle heavily ringed with prominent bristles throughout or certain areas of the body.
2. Anterior end with 4 sensory bristles.
3. Amphids crescent-shaped or pump- shaped.
4. Marine and free-living nematodes.
Examples:
Desmoscolex, Greefiella, Epsilonema.
Order 6. Monohysterida:
1. Cuticle smooth or slightly ringed, often with bristles.
2. Anterior end with 4, 6, or 8 bristles or multiple of the above numbers.
3. Amphids circular.
4. Mostly marine, some fresh water and some terrestrial.
Examples:
Monohystera, Saiphonolaimus.
Order 7. Araeolaimida:
1. Cuticle smooth, sometimes with bristles.
2. Labial papillae present.
3. Four cephalic bristles at the anterior end.
4. Amphids spiral.
Examples:
Plectus, Odontophora, Wilsonema.
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