Q.35 Given below are two statements:
Statement I: Sponges are the only major phylum that lack nerves.
Statement II: The simplest nervous system occurs in platyhelminthes.
In the light of the above statements, choose the
correct answer from the options given below:
- Both Statement I and Statement II are correct
- Both Statement I and Statement II are incorrect
- Statement I is correct but Statement II is incorrect
- Statement I is incorrect but Statement II is correct
Sponges lack nerves, but platyhelminthes do not have the simplest nervous system—cnidarians do.
Both statements contain inaccuracies: sponges are nerve-less, yet platyhelminthes’ nerve net exceeds Cnidaria’s primitive version.
Question Breakdown
Statement I correctly identifies sponges (Porifera) as the only major phylum without nerves or neurons, relying on cellular signaling. Statement II errs—Cnidaria (jellyfish, hydra) possess the simplest nerve net, while platyhelminthes (flatworms) have a more organized ladder-like system with brain ganglia.
Option Analysis
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Both correct: Incorrect. II overstates platyhelminthes simplicity.
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Both incorrect: Wrong. I holds true.
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I correct, II incorrect: Correct answer. Sponges: no nervous system; Cnidaria: nerve net; Platyhelminthes: cerebral ganglia + longitudinal cords.
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I incorrect, II correct: False. Sponges uniquely lack nerves among metazoans.
Correct Answer
Statement I is correct but Statement II is incorrect.
Nervous System Evolution
Sponges are the only major phylum that lack nerves, using choanocytes and calcium waves for coordination—no neurons or synapses exist. The simplest nervous system occurs in platyhelminthes? False—Cnidaria’s diffuse nerve net precedes flatworms’ advanced setup.
Statement I: Sponges Nerve-Free
Porifera uniquely lack nervous tissue among animals, with recent studies finding neural gene homologs but no true neurons. Flask cells enable larval phototaxis via signaling, not nerves.
Statement II: Cnidaria Simpler
Platyhelminthes feature anterior brain, ventral nerve cords, and commissures—more complex than Cnidaria’s net of interconnected neurons without centralization. Hydra exemplifies the baseline.
Phylum Nervous System Complexity Porifera None Basal signaling Cnidaria Nerve net Simplest Platyhelminthes Brain + cords Organized Exam Strategy
NEET/GATE tip: Sequence—Sponges (0), Cnidaria (net), Platyhelminthes (ladder), Annelida (segmented). Statement I textbook fact; II common distractor.
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