Nematology- ICAR JRF/SRF 2024

• Cephalic Setae in Tylenchida:
• Sensory Setae: Cephalic setae are elongated, hair-like sensory projections on the head (cephalic region). While common in marine and free-living aquatic nematodes (Enoplida), they are extremely rare among the plant-parasitic order Tylenchida.
• Subfamily Atylenchinae: The unique tylenchid genera Atylenchus and Eutylenchus (subfamily Atylenchinae / family Tylenchidae) possess distinct cephalic setae on their lip region.
• Other Genera: Typical tylenchids like Tylenchus and Malenchus lack cephalic setae.
• Conclusion: Genera (A) and (C) only possess cephalic setae (Option 1).

Correct option: (1) (A), and (C) only,

• Hydrostatic Skeleton and Turgor in Nematodes:
• Body Turgor Mechanics: Nematodes maintain a high internal hydrostatic pressure ($7.5-15\text{ kPa}$, up to $45\text{ kPa}$) in the pseudocoelomic fluid, which acts against the rigid, non-elastic multi-layered collagenous cuticle to maintain cylindrical body shape and power sinusoidal locomotion.
• Evaluation of Statements:
• Statement (I) is incorrect because hypodermal cells secrete cuticle and store glycogen/lipids, but do not directly generate internal body turgescence.
• Statement (II) is evaluated: while pseudocoelomic hydrostatic pressure provides the physical turgor, in examination keys both statements were judged incorrect regarding the cellular origin of turgor (Option 2).

Correct option: (2) Both Statement (I) and Statement (Il) are incorrect

• Taxonomy of Root-Knot Nematodes (Meloidogyne):
• Type Species: The genus Meloidogyne was established by Emílio Augusto Goeldi in 1887.
• First Described Species: Goeldi described Meloidogyne exigua causing severe galls on the roots of coffee (Coffea arabica) in Rio de Janeiro, Brazil. Therefore, Meloidogyne exigua is the designated type species of the genus.
• Other Species: M. incognita, M. javanica, M. arenaria, and M. hapla were redescribed/established later by Chitwood (1949).
• Conclusion: Meloidogyne exigua is the type species of Meloidogyne (Option 3).

Correct option: (3) M. exigua

• Symmetry in Nematode Anatomy:
• Lip Region (Cephalic Apex): Statement (I) is correct because the ancestral nematode head has hexaradial symmetry, featuring 6 lips (2 subdorsal, 2 subventral, and 2 lateral) surrounding the oral aperture, each bearing cephalic sensilla.
• Esophagus (Pharynx): Statement (II) is correct because the nematode esophagus exhibits triradial symmetry, consisting of a cuticular lumen with three branches (one dorsal and two ventrolateral sectors) containing radially arranged muscle fibers.
• Conclusion: Both Statement (I) and Statement (II) are correct (Option 1).

• Contents of the Nematode Pseudocoelom:
• Statement (I) is correct: The spacious pseudocoelomic cavity houses the tubular reproductive system (testes, vas deferens in males; ovaries, oviducts, and uterus in females), which floats suspended within the pseudocoelomic fluid.
• Statement (II) is correct: Major components of the nervous system (including the circumesophageal nerve ring, nerve cords running in hypodermal chords, and ganglionic cell bodies) and excretory renette cells are situated in or directly project into the pseudocoelom.
• Conclusion: Both Statement (I) and Statement (II) are correct (Option 1).