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The animals belonging to the invertebrate group of Kingdom Animalia are highly diverse and are divided into several phyla. The classification is based upon several factors, such as symmetry, the shape of the body, presence or absence of segmentation, presence or absence of exoskeleton, and a few more.

A land snail, an octopus, and a clam are all members of the phylum mollusc. The common features of all the members of this phylum are unsegmented soft bodies, three distinct regions in the body (visceral mass, head, and foot), and a body covering a mantle.

Thus, the mantle is common in clams, land snails, and octopuses (mollusc members).

Therefore, the given option is true.

The term radula describes a feeding structure found in most members of the mollusc. It has a tiny teeth-like appearance and is present within the mollusc member鈥檚 buccal cavity. An exception to this structure is found in bivalve molluscs (such as clams) which contain cilia instead of radula.

Thus, the structure of radula is common to land snails and octopuses, but it is absent in clams.

Therefore, the given option is false.

Respiration is an important physiological activity found in all life forms. The mollusc members that inhabit the aquatic environment respire through the gills present in their mantle structure, while the terrestrial molluscs respire through the lungs.

Thus, gills are absent in the case of land snails.

Therefore, the given option is false.

In biology, cephalization refers to how the nervous system components aggregate towards one region of the body and constitute a distinct head structure. It is found in all mollusc members except for the bivalve molluscs (clams).

Thus, distinct cephalization is not found in clams.

Therefore, the given option is false.