Which of the following character is unique to Tusk-shell?

Step-by-step solution

Phylum Mollusca: This is the second largest animal phylum. Molluscs are terrestrial or aquatic (marine or freshwater) 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