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What is the primary reason that distinguishing nematode species is challenging?
What percentage of described nematode genera are marine dwellers?
Which of the following statements about nematode morphology is true?
In which ecological habitats can nematodes be found?
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What type of body cavity do nematodes have?
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How do nematodes transport nutrients within their bodies?
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Which of the following types of nematodes is beneficial as entomopathogens?
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What distinguishes nematodes as one of the most abundant multicellular animals on Earth?
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What is a key characteristic of male nematodes during copulation?
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What unique feature is associated with nematode sperm?
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Which reproductive mode allows some nematodes to self-fertilize?
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How do free-living roundworms develop their offspring?
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What is the primary criterion for traditional classification of nematodes?
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What modern technique is used for the classification of nematodes?
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Which class of nematodes lacks phasmids?
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What percentage of plant-parasitic nematodes are found in the Tylenchids group?
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What structural feature distinguishes Chromadorea from Enoplea?
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Which statement about plant parasitic nematodes is correct?
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What is the first stage in the life cycle of a typical phytonematode?
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During the molting process, which of the following occurs?
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What type of stylet is characteristic of the Chromadorea class?
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What is the usual duration of the life cycle for most phytonematodes?
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How do nematodes acquire and transmit viruses?
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What characterizes the feeding mechanism of plant parasitic nematodes?
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What form do Meloidogyne juveniles take after developing inside the root?
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What is the primary characteristic of the male Meloidogyne after it has developed?
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During the lifecycle of Meloidogyne, what do the females do after developing inside the roots?
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Which type of phytonematode is characterized as a sesile endoparasite?
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What do ectoparasitic feeders typically do?
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After a favorable feeding period, how many molts do the juvenile individuals undergo?
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Which of the following nematodes are known as migratory endoparasites?
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What defines the feeding behavior of surface feeders in phytonematodes?
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What is one way to diagnose nematode-induced plant diseases without visible symptoms?
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Which of the following extraction methods uses nested sieves?
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What structure is commonly looked for when diagnosing root knot nematodes?
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What type of nematode is associated with the term 'nema wool'?
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In nematode sampling, what must be considered when selecting sample times?
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Which method is effective in extracting all life stages of nematodes?
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What is one benefit of using a composite set of samples in nematode diagnostics?
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What distinguishes the Oostenbrink Elutriator as an extraction method?
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Study Notes
Introduction to Nematodes
- Nematodes, roundworms of Phylum Nematoda, are the second most abundant multicellular animals, following insects.
- Over 80,000 genera described, with approximately 15,000 being parasitic.
- Occupy diverse habitats including marine, freshwater, soil, and as parasites of animals and plants.
- Composition of the nematode body is predetermined in cell count; growth occurs through cell division.
- 50% of genera are marine, 25% free-living, 15% animal parasites, and 10% plant parasites.
- Some nematodes are beneficial, serving as entomopathogens.
Nematode Morphology
- Nematodes possess unsegmented, bilaterally symmetrical bodies with three tissue layers: ectoderm, mesoderm, and endoderm.
- Lacking a circulatory system, they transport nutrients via a pseudocoelom filled with fluid.
- They have a complete digestive system with specialized orifices for ingestion and excretion.
- Males are typically smaller than females and have curved tails for copulation purposes.
- Nematode sperm is unique, lacking globular protein G-actin, and may be either embryonated or unembryonated when laid.
Reproduction
- Free-living nematodes hatch from eggs and develop into larvae, while parasitic nematodes have complex life cycles.
- Some nematodes are hermaphroditic and may self-fertilize, retaining eggs until ready to hatch.
- Meloidogyne species can reproduce sexually, facultatively, or via various forms of parthenogenesis.
Nematode Taxonomy and Classification
- Traditional classification relies on morphological features, particularly phasmid presence.
- Modern classification is based on small subunit ribosomal DNA (SSU rDNA), identifying two classes: Enoplea and Chromadorea.
- Enoplea includes agriculturally important orders, while Chromadorea contains primarily plant parasites, constituting 94% of such nematodes.
Morphological Characteristics
- Chromadorea: pore-like amphids, annulated cuticle, and a three-part esophagus with multiple glands.
- Enoplea: pocket-like amphids, smooth or finely striated cuticle, cylindrical or bottle-shaped esophagus.
Plant Parasitic Nematodes
- Possess a specialized stylet for penetrating host cells and extracting cell fluids.
- Stylet types differentiate saprophytic from plant-parasitic nematodes: stomatostylet (Chromadorea) and odontostylet (Enoplea).
Life Cycle of Phytonematodes
- Typical life cycle lasts 3-4 weeks from egg-laying to the appearance of the next generation.
- Development involves multiple juvenile stages, with molting critical for growth and transition.
Feeding Types of Phytonematodes
- Surface feeders: feed on root epidermal cells (e.g., Trichodorus spp., Paratylenchus spp.).
- Ectoparasitic feeders: penetrate root cortex cells (e.g., Belonolaimus spp., Rotylenchus spp.).
- Migratory endoparasites: actively enter and move within plant tissues (e.g., Pratylenchus spp.).
- Sessile endoparasites: remain fixed in one position post-penetration (e.g., Meloidogyne spp., Heterodera spp.).
Diagnosis of Nematode-Induced Diseases
- Symptoms include galls, cysts, stubby roots, and internal leaf necrosis.
- Soil and plant tissue assays are essential for diagnosis, often requiring microscopy for nematode identification.
- Nematodes often congregate in "hot spots," making careful sampling crucial for accurate population assessment.
Extraction Methods
- Common methods include washing and sieving through nested sieves, Baermann funnel, and centrifugation-floatation techniques.
- Specific methods for cyst nematodes include washing and drying, Oostenbrink elutriator, and Fenwick can.
Summary
- Nematodes are integral to ecosystems, with various forms affecting agriculture and plant health.
- Understanding their morphology, life cycle, reproduction, and feeding habits is essential for their management and control.
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Description
This quiz covers the fundamental aspects of nematodes, including their classification, habitats, and biological characteristics. Explore their morphology, body structure, and the roles they play in ecosystems, from being beneficial organisms to their parasitic nature.
