Final answer:
Mollusks have a distinct body plan characterized by a hard outer shell, a head region with tentacles, a muscular foot, and a mantle that covers the body and secretes a calcium carbonate shell.
Step-by-step explanation:
Mollusks are a diverse phylum of invertebrates that include species such as snails, clams, and octopuses. They have a distinct body plan characterized by a hard outer shell, a head region with tentacles, a muscular foot, and a mantle that covers the body and secretes a calcium carbonate shell.
For example, the head of a snail may have eyes at the base of the tentacles, which are used for sensing the environment. The muscular foot can be used for crawling or burrowing, while the tentacles can be used for feeding. The mantle, which is a fold of tissue present in all mollusks, carries out various functions such as respiration, reproduction, and shell formation.