BSc 1st Year Lower Non-chordates General Characters of Phylum Nematoda Sample Model Practice Question Answer Papers

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BSc 1st Year Lower Non-chordates General Characters of Phylum Nematoda Sample Model Practice Question Answer Papers

Q.1. Classify Nematoda or Nemathelminthes mentioning the characters of its orders. Cite an example of each order. 

Ans. 1. Nematodes are widely distributed free living as well as parasitic worms.

2. Roundworms are elongated, cylindrical, and soft-bodied worms with tapering ends. 

3. Body is unsegmented but may be wrinkled. It is not distinguished into regions.

4. Body unpigmented being either white or with a yellowish tinge.

5. Body triploblastic and bilaterally symmetrical.

6. Body wall has a thick outer cuticle, syncytial epidermis or hypodermis and longitudinal muscle layer; circular muscles are absent.

7. Longitudinal muscle fibres are arranged into four quadrants.

8. Body cavity is a pseudocoel.

9. Coelom, circulatory system and respiratory system and cilia are absent.

10. Excretory system consists of one or two gland-like organs called renette cells or H-shaped system of canals. Flame cells are absent.

11. Nervous system consists of nerve ring around pharynx and four longitudinal nerve trunks which run within four epidermal chords.

12. Sense organs are sensory papillae called amphids on head and phasmids at the posterior end.

13. Sexes are separate and exhibit sexual dimorphism. The posterior end of female is straight while in male the tail is curved.

14. Fertilisation is internal. Female may be oviparous or ovoviviparous. Cleavage is determinate. (BSc 1st Year Lower Non-chordates General Characters of Phylum Nematoda Sample Model Practice Question Answer Papers)

Classification

Nematoda is divided into two classes : Aphasmida (Adenophorea) and Phasmidia (Secernentea).

Class 1. Aphasmida (Adenophorea)

1. Posterior or caudal sensory organs (phasmids) absent.

2. Anterior sensory organs (amphids) not pore-like.

3. Caudal adhesive organ present.

4. Cephalic organs, setae and hypodermal glands present.

5. Epidermal cells uninucleate. Cuticle four layered.

ORDER 1. Enoploidea

1. Anterior end with six labial papillae and 10-12 sensory bristles.

2. Amphids cyanthiform or pocket-like, elongated or pore-like.

3. Cuticle with bristles.

4. Intestine ends in a blind pouch.

5. Free living and marine; small to moderate in size.

Examples : Enoplus, Metonchdiamus, Anticoma, Trilobus,

ORDER 2. Mermithoidea

1. Anterior end with 16 labial papillae; sensory bristles absent.

2. Amphids cyanthiform, large, sickle-shaped or small and pore-like.

3. Cuticle smooth and without bristles.

4. Oesophagous long; intestine ends in a blind pouch.

5. Adults free living, larvae parasite in invertebrates; large in size.

Examples : Mermis, Paramermis; Allomermis and Agamermis.

ORDER 3. Dorylaimoidea

1. Anterior end with 6-10 labial papillae, arranged in a circle.

2. Cuticle without bristles.

3. Amphids sickle-shaped.

4. Buccal cavity with protrusible spear.

5. Free living; common in soil and freshwater.

Example: Dorylaimus.

ORDER 4. Desmoscolecoidea

1. Anterior end with four sensory bristles or papillae.

2. Head armoured.

3. Amphids crescent-shaped or hemispherical.

4. Cuticle heavily ringed.

Examples : Desmoscolex, Episilonema, Tricoma.

ORDER 5. Monohysteroidea

1. Anterior end with 4, 6, 8 or many sensory bristles.

2. Amphids circular.

3. Cuticle smooth or slightly ringed with scattered bristles.

4. Small sized, free-living, mostly marine, some freshwater.

Examples : Monohystera, Siphonolaimus, Plectus.

ORDER 6. Chromadoroidea

1. Amphids spiral.

2. Cuticle smooth or ringed with bristles.

3. Anterior end with six lips and 10 papillae or bristles arranged in a circle.

4. Buccal cavity with teeth and pharynx with posterior bulb.

ORDER 7. Dioctophymatida

1. Mouth without lips but with papillae.

2. Pharynx elongated without bulb.

Examples : Diatophyma, Hystrichis.

Class 2. Phasmidia 

1. Phasmids present

2. Amphids pore-like

3. Caudal adhesive glands absent.

4. Cephalic sensory organs present, setae or papillae are not found in females.

5. Epidermal cells uni or multinucleate. Cuticle two or four layered.

ORDER 1. Rhabditoidea

1. Cuticle smooth or ringed.

2. Sensory bristles on the head in the form of papillae arranged in two rings.

3. Male with genital papillae and copulatory spicules. The dorsal wall of spicules is thickened to form a gubernaculum. (BSc 1st Year Lower Non-chordates General Characters of Phylum Nematoda Sample Model Practice Question Answer Papers)

4. Small or moderate-sized worms; free-living or parasites in animals and plants.

5. Pharynx with two bulbs: one without valves and the other with valves.

Examples: Rhabditis, Heterodera, Tulenchus, Anguina.

ORDER 2. Trichuroidea or Trichinelloidea

1. Body filiform anteriorly.

2. Mouth without lips; pharynx slender without bulb.

3. Male without copulatory apparatus or contains an eversible spicule or cirrus.

Examples: Trichiuris, Trichinella, Capillaria, Cystopsis.

ORDER 3. Oxyuroidea

1. Pin-shaped, small worms, parasitic.

2. Mouth surrounded by 3-6 simple lips.

3. Pharynx with posterior bulb. Bulb contains valves.

4. Female has long and slender tail.

Examples: Oxyuris, Enterobius, Heterakis.

ORDER 4. Ascaroidea

1. Large-sized worms; endoparasites in vertebrates.

2. Mouth surrounded by three lips.

3. Pharynx without bulb-like enlargement.

4. Tail coiled ventrally in male.

5. Males smaller than females and have equal-sized copulatory spicules.

Examples : Ascaris, Ascaridia, Parascaris, Toxascaris.

ORDER 5. Filarioidea

1. Filiform, slender worms; parasites of vertebrates.

2. Labial papillae six; mouth without lips.

3. Buccal and pharyngeal bulb absent. Pharynx is divided into anterior muscular and posterior glandular parts. (BSc 1st Year Lower Non-chordates General Characters of Phylum Nematoda Sample Model Practice Question Answer Papers)

4. Copulatory spicules in male dissimilar and unequal.

5. Males smaller than females; tail coiled in males.

Examples : Wuchereria, Microfilaria, Loa.

ORDER 6. Spiruroidea

1. Slender worms, parasite in vertebrates.

2. Mouth with two lateral unlobed lips or trilobed lips.

3. Sensory papillae on head in two circles of 6 and 4 or 6 and 8.

4. Pharynx with bulb muscular anteriorly and glandular posteriorly.

Examples : Gnathostoma, Spiroxys, Pneumonema, Rictularia, Oxyspirura.

ORDER 7. Strongyloidea

1. Parasitic worms of small or moderate size.

2. Mouth without lips but with leaf crowns.

3. Buccal capsule well-developed; pharyngeal bulb absent.

4. Female with ovijector and male with expanded copulatory bursa.

Examples : Ancylostoma, Strongylus, Necator.

ORDER 8. Dracunculoidea

1. Large sized worms; parasites in vertebrates.

2. Lips and buccal capsule absent.

3. Mouth surrounded by rings of papillae 4 or 8 in number.

4. Pharyngeal bulb absent; pharynx muscular anteriorly and glandular posteriorly.

5. Copulatory spicules filiform and equal.

6. Males smaller than females.

Examples : Dracunculus, Philometra.

ORDER 9. Rhabdiasoidea

1. Pharyngeal bulb absent.

2. Cuticle smooth.

3. Pharynx without bulb.

4. Life cycle includes both parasitic and free-living stages. The parasitic stage is adult. (BSc 1st Year Lower Non-chordates General Characters of Phylum Nematoda Sample Model Practice Question Answer Papers)

5. Parasites may be protandrous hermaphrodites or parthenogenetic females.

Examples: Rahbdias, Strongyloides.

BSc 1st Year Lower Non-chordates General Characters of Phylum Nematoda Sample Model Practice Question Answer Papers

BSc 1st Year Lower Non-chordates General Characters of Phylum Nematoda Sample Model Practice Question Answer Papers

BSc 1st Year Sample Model Practice Mock Test Question Answer Papers

BSc 1st Year Lower Non-chordates General Characters of Phylum Nematoda Sample Model Practice Question Answer Papers

BSc 1st Year Lower Non-chordates General Characters of Phylum Nematoda Sample Model Practice Question Answer Papers