Q.40 Ascaris lumbricoides is
(1) Acoelomate
(2) Pseudocoelomate
(3) Coelomate
(4) Nephrocoelomate
Ascaris lumbricoides: The Classic Pseudocoelomate Parasite
Ascaris lumbricoides, the human roundworm, infects ~800 million people worldwide, causing ascariasis. The question “Ascaris lumbricoides is” tests animal body cavity classification—a fundamental zoology concept. The correct answer is (2) Pseudocoelomate. This distinction reveals evolutionary relationships in phylum Nematoda.
Body Cavity Types: The Evolutionary Progression
Body cavities form during embryogenesis and define animal phyla:
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Acoelomate: No body cavity (solid mesoderm).
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Pseudocoelomate: False cavity between mesoderm and endoderm.
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Coelomate: True coelom fully lined by mesoderm.
Understanding this hierarchy is crucial for NEET, CSIR NET, and invertebrate zoology.
Correct Answer: Option (2) Explained
(2) Pseudocoelomate
Ascaris has a pseudocoelom—a fluid-filled cavity not fully lined by mesoderm. Key features:
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Forms from embryonic blastocoel persistence.
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Provides hydrostatic skeleton for locomotion.
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Houses organs but lacks peritoneum lining.
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Typical of Nematoda, Rotifera, minor phyla.
Cross-section view: Gut (endoderm) surrounded by pseudocoelom, then body wall muscles (mesoderm). This enables turgor pressure movement.
Why Not the Other Options?
Eliminate systematically:
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(1) Acoelomate
No body cavity at all—mesoderm fills space entirely (e.g., Platyhelminthes like Taenia). Ascaris clearly has a cavity. -
(3) Coelomate
True coelom with mesodermal peritoneum lining both sides (e.g., Annelida, Chordata). Nematodes lack this complete lining. -
(4) Nephrocoelomate
Obscure term; refers to coelom derived from nephrotome (kidney precursor) in vertebrates. Not standard for invertebrates like Ascaris. Distractor option.
| Body Cavity | Lining | Examples | Ascaris? |
|---|---|---|---|
| Acoelomate | None | Flatworms | No |
| Pseudocoelomate | Partial | Nematodes, Rotifers | Yes |
| Coelomate | Complete mesoderm | Earthworms, Humans | No |
Biological Significance and Exam Tips
Pseudocoel aids Ascaris survival: nutrient transport, waste removal, flexibility through intestine. Females (25-35 cm) lay 200,000 eggs/day. Memorize: Roundworms = pseudocoelomates always.
This classification links to phylogeny—pseudocoelomates bridge acoelomates and eucoelomates.
