Mollusk Anatomy & Key Features — NEET Biology
📚 Practice ConceptThis is the second largest animal phylum. Molluscs are terrestrial or aquatic (marine or fresh water) having an organ-system level of organisation. They are bilaterally symmetrical, triploblastic and coelomate animals. Body is covered by a calcareous shell and is unsegmented with a distinct head, muscular foot and visceral hump. A soft and spongy layer of skin forms a mantle over the visceral hump. The space between the hump and the mantle is called the mantle cavity in which feather like gills are present. They have respiratory and excretory functions. The anterior head region has sensory tentacles. The mouth contains a file-like rasping organ for feeding, called radula.
Which of the following statements regarding the characteristics of Phylum Mollusca are correct? S1: The body of molluscs is distinctly divided into a head, a muscular foot, and a visceral hump, but remains unsegmented. S2: The mantle, a soft and spongy layer of skin covering the visceral hump, is responsible for secreting the calcareous shell. S3: Feather-like gills, situated in the mantle cavity, perform both respiratory and excretory functions. S4: All molluscs universally possess a file-like rasping organ called radula in their mouth, used for feeding. S5: Molluscs are typically dioecious, oviparous, and exhibit indirect development, often involving free-swimming larval stages.
View solution & NCERT explanation
Correct answer: B — S1, S2, S3 and S5
This question evaluates the understanding of specific structural and functional characteristics of Phylum Mollusca. S1: Correct. NCERT states that the mollusc body is 'unsegmented with a distinct head, muscular foot and visceral hump.' (Page 44, Phylum Mollusca section). S2: Correct. NCERT describes the mantle as 'A soft and spongy layer of skin forms a mantle over the visceral hump.' The mantle is known to secrete the calcareous shell, which is mentioned as covering the body. (Page 44, Phylum Mollusca section). S3: Correct. NCERT explicitly mentions, 'The space between the hump and the mantle is called the mantle cavity in which feather like gills are present. They have respiratory and excretory functions.' (Page 44, Phylum Mollusca section). S4: Not correct. NCERT states, 'The mouth contains a file-like rasping organ for feeding, called radula.' However, the quantifier 'All molluscs universally possess' makes this statement incorrect, as some molluscs (e.g., bivalves) lack a radula. NCERT implies it's a general feature but doesn't explicitly state 'all' or 'some'. In the context of competitive exams, 'all' for radula is generally considered false. (Page 44, Phylum Mollusca section). S5: Correct. NCERT states, 'They are usually dioecious and oviparous with indirect development.' (Page 45, Phylum Mollusca section). Therefore, statements S1, S2, S3, and S5 are correct. This highlights the importance of precise language and quantifiers in biological statements.
What does NCERT say about This second largest animal?
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