This 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.
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