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In this article we will discuss about of Phylum Nematoda:- 1. Definition of Phylum Nematoda 2. General Characteristic Features of Phylum Nematoda 3. Classification.
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.
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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.
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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.
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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.
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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:
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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):
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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.
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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.
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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.
Class 2. Secernentea or Phasmida:
Characters:
1. Caudal phasmids present.
2. Labial amphids pore-like.
3. Excretory system canal-like and comparatively more complex.
4. Epidermal and caudal adhesive glands absent.
5. Males with a single testis.
6. Mostly parasitic.
7. Free-living species are largely terrestrial.
It includes certain important orders:
Order 1. Rhabditida:
1. Cuticle smooth and ringed.
2. Sensory bristles in 2 rings; the outer ring 4, 6 or 10 bristles and inner ring of 6 bristles.
3. Pharynx with a posterior bulb.
4. Copulatory spicules with gubernaculum in males.
5. Free-living and parasitic nematodes.
Examples:
Rhabditis, Heterodera, Bunonema.
Order 2. Strongylida:
1. Lips absent.
2. Males with two spicules.
3. A true copulatory bursa is present.
4. Buccal capsule well developed.
5. Pharynx without bulb.
6. Vertebrate parasites.
Examples:
Ancylostoma duodenale (Hookworm), Strongylus, Trichostrongylus (Hair worm), Ne-cator.
Order 3. Oxyurida:
1. Small to moderate in size.
2. Copulatory spicules present in males.
3. Tail of females long, narrow and pointed.
4. Mouth provided with 3-6 simple lips.
5. Pharynx with a valvular posterior bulb.
6. Caudal alae present.
7. Invertebrate and vertebrate parasites.
Examples:
Oxyuris, Enterobius vermicularis (Pinworm), Heterakis gallinae, Thelastoma, Aspiculuris.
Order 4. Ascaridida:
1. Large stout nematodes residing in the intestine of vertebrates as parasites.
2. Mouth provided with 3 prominent lips.
3. Males possess 2 equal or almost equal copulatory spicules.
4. Buccal capsule absent.
5. Pharynx with or without a posterior bulb.
6. Tail of females blunt.
7. Oviparous.
Examples:
Ascaris (Ascaris lumbricoides, Ascaris megalocephala, Ascaris suillas), Parascari, Toxocara.
Order 5. Spirurida:
1. Thread-like, moderate to large size.
2. Females larger than males.
3. Mouth usually provided with two lateral lips.
4. Pharynx without bulb.
5. Males with two unequal copulatory spicules but do not have bursa or caudal alae.
6. Oviparous or viviparous.
7. Parasites of vertebrates and with a blood sucking invertebrate as intermediate host.
Examples:
Spirura, Wuchereria bancrofti (Filaria), Loa loa (Eye worm), Brugia, Onchocerca, etc.
Order 6. Trichuroida (= Trichinelloidea):
1. Anterior part of the body whip-like.
2. Mouth without lips.
3. Pharynx slender.
4. Males with one or without spicule.
5. Males are either with bursa or with cirrus.
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6. Life cycle simple—no intermediate host.
7. Commonly known as whip worms.
Examples:
Trichuris (Parasites of mammals), Trichinella spiralis (Trichinia worm).
Order 7. Camallanida:
1. Thread-like; females larger than males.
2. Lips absent.
3. Buccal capsule large or absent.
4. Spicules of males of same size.
5. No bursa in males.
6. Adult females with degenerated bursa.
7. Mostly oviparous.
8. Parasites of vertebrates.
Examples:
Camallanus, Procamallanus, Dracunculus medinensis (Guinea-worm), Philometra.
