General character, classification upto order of phylum Nematoda

General character:

The distinguishing feature of phylum Nematoda is as discuss below.

1. Widely distributed,aquatic or terrestrial, and parasitic or free-living.
2. Body elongated, cylindrical , unsegmented, worm-like , bilaterally symmetrical , and tapering towards both ends.
3. Body trophoblastic with organ- system grade of organization.
4. Body wall with thick resistant cuticle, cellular or syncytial epidermis, and only longitudinal muscle fibres in four bands.
5. True coelom absent. persistent blastocoel or pseudocoel present not lined by mesoderm.
6. No cilia, no circulatory and no respiratory system.
7. Digestive system complete with the anus, either muscular pharynx and non-muscular intestine.
8. Excretory system of glandular organ or canals or both.Flame cells absent.
9. Nervous system with the circumfering ring and anterior and posterior nerves.
10. Sense organs poorly developed, in the form of small papillae and aphids near on two body ends.
11. Dioecious with sexual dimorphism Male smaller than female. Gonads simple and coiled. Male genital ducts lead into the cloaca.Female genital ducts ith a separate opening.No asexual reproduction.
12. Fertilization internal Development usually direct, with or without an intermediate host.

Classification of phylum Nematoda:

Nematoda is among the most numerous of any phylum.Every fistful of soil contains thousand of them.About 15,000 species of nematodes are known at present. Their classification is difficult due to much diversity in the form and structure.Chitwood (1933) divided them into to classes. they are Phasmidia and Aphasmidia,on the basis of presence or absence of plasmid. They are group into 17 orders, but only some important orders have been included below.

Class 1. Aphasmidia:Some characterised of class Aphasmidia is below .It is divided into 6 order which is discussed below.

1. Plasmids (caudal sensory organs) absent
2. Amphids (anterior sense organ) of various types,rarely pure- like.
3. No excretory system. If present, poorly developed.
4. Mesenterial tissue well developed.
5. Caudal adhesive glands present.

Order 1. Enoploidea:

1. Anterior end with six labile papillae and 12- 13 sensory bristles.
2. Cuticle usually with bristles.
3. Amphids cyathiform.
4. Chiefly marine, free-living.

Example: Enoplus, Metonchdiamus.

Order 2. Dorylaimoidea

1. Anterior end with 6-10 papillae.
2. Cuticle smooth, no bristles.
3. Amphids cyathiform.
4. Buccal cavity with a protrusible spear.
5. Free living in soil and fresh water.

Example: Dorylaimus, Tylencholaimus.

Order 3. Mermithid:

1. Large sized.
2. Anterior end with 16 labile papillae and no sensory bristles.
3. Amphids cyathiform or reduced.
4. Oesophagus long leading into the blind intestine.
5. Amphids cyathiform or reduce.
6. Larvae parasitic invertebrates, adults free_living.

Example : Mermis, Agamermis, Parameris,

Order4. Chromadoroidea.

1. Small sized.
2. Cuticle smooth or ringed: with heavy bristles.
3. Amphids spiral.
4. Buccal cavity with teeth.
5. Pharynx with the posterior bulb.
6. Mostly marine.free living.

Example: Halichoanolaimus.

Order 5. Monohysteroidea.

1. Small sized.
2. Aphids circular.
3. Cuticle smooth or slightly ridged, often with bristles.
4. Anterior end with 4,6, 8,or many sensory bristles.
5. Free-living: mostly marine, some fresh- water, some terrestrial.

Example: Desmoscolex, Epsilonema.

Class 2. Phasmidia: Some character feature of this class is discussed below . It is further divided up to order 10 which is discussed below.

1. Plasmids present.
2. Amphids pore- like.
3. The excretory system developed.
4. Mesenterial tissue weakly developed.
5. No caudal adhesive glands.

Order 1. Trichuroidea

1. Body filiform anteriorly.
2. Mouth without lips: pharynx slender.
3. Female with one ovary and male ith one or none spicule.
4. Parasites of vertebrates.

Example: Trichuris, Trichinella,

Order 3. Dioctophymoidea

1. Large worms.
2. Mouth without lips: with 6, 12, or 18, papillae.
3. Female with one ovary and male ith one spicule and muscular bursa.
4. Parasites of vertebrates, birds,and mammal.

Example: Dioctophyma, Hysterics.

Order 3: Rhabditoidea

1. Small to modern sized.
2. Cuticle smooth or ridged.
3. Sensory bristles as papillae in two ring an inner ring of 6 and outer ring 4,6, or 10.
4. Copulation spicules in male accompanied by gubernaculum.
5. Free - living or parasite in animals and plants.

Example: Rhabditis, Heterodera.

Order.4. Rhabdiasoidea

1. Medium sized.
2. Cuticle smooth.
3. No pharyngeal bulb.
4. Parasite stage in vertebrates is either hermaphroditic or parthenogenetic.

Example: Rhabdias, Strongyloides.

Order.5 Oxyuroidea:

1. Pin shaped small worms.
2. Mouth surrounded by 3-6 simple tips.
3. Pharynx with Vascular posterior bulbs.
4. Female with a long pointed tail.
5. Parasitic in invertebrates and vertebrates.

Example: Oxyuris, Enterobius.

Order 6. Ascaroidea

1. Large-sized worms.
2. Mouth surrounded by 3 lips.
3. Pharynx without bulb.
4. Parasites of vertebrates.
5. Parasitic in vertebrates.

Example:Ascaris, Ascaridia.

Order 7. Strongyloides.

1. Mouth without lips but with leaf crowns.
2. Buccal capsule well developed.
3. No pharyngeal bulb.
4. Male with expanded copulatory bursa: female usually with objector.
5. Parasites of vertebrates.

Example :Nectar, Ancylostoma, Strongylus.

Order 8. Spiruroidea:

1. Mouth with two lateral lips.
2. Pharynx with bulb, muscular anteriorly and glandular posteriorly.
3. No copulatory bursa in male but with spirally coiled tail.
4. Parasitic in animals.

Example: Thelazia, Gnathostoma, Spiroxys.

Order 9. Dracunculoidea:

1. No lips. or buccal capsule.
2. Mouth surrounded by a ring of papillae.
3. No pharyngeal bulb, pharynx muscular anteriorly and glandular posteriorly.
4. Male without copulatory bursa.
5. Parasitic of vertebrates.

Example: Dracunculus, Philometra.

Order 10 . Filarioidea

1. Filmform slender worms.
2. No lips and buccal capsule.
3. Six labile papillae present.
4. No pharyngeal bulb.
5. Male small w ith coiled tail.
6. Microfilaria in blood or skin and develop in blood -sucking insects.
7. Parasites of vertebrates.

Example.Wucheria, Microfilaria, loa.

Reference:

Aggarwal Sarita. A Text Book of Biology,New Delhi.: Madhuban Educational Books, 2011.

Bhamrah, H.S., and Kavita, Juneja. A Text Book of Invertebrates, New Delhi: Anmol Publications Pvt Ltd, 2011.

Jordan E.L. and P. S., Verma. Invertebrate Zoology, New Delhi,: S. Chand and Company Pvt. Ltd., 2011.

Kotpal, R. L., Modern Text Book of Zoology: Invertebrates, New Delhi, India: Rastogi Publications,2011.

http://www.biologydiscussion.com/

http://www.parasitesinhumans.org/

https://web.stanford.edu/class/

https://en.m.wikipedia.org/wiki/Nematoda