In which of the following animals is the brain absent but nerve cells are present?
Correct answer: D. Hydra
- A. Sponge
- B. Earthworm
- C. Cockroach
- D. Hydra
Explanation
Hydra belongs to the phylum coelenterata and has nerve cells but no brain. Its nervous system consists of nerve cells and their processes. Sensory cells are also present. Sponges do not have nerve cells as they lack a nervous system. Earthworm (annelida) has a nervous system consisting of a circumenteric nerve ring and a solid, double, midventral nerve cord with ganglia. Cockroach (arthropoda) has the same nervous system as the earthworm.
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