Mollusks, such as snails, clams, and octopuses, possess a type of external skeleton known as an exoskeleton. This exoskeleton is primarily composed of calcium carbonate and serves several essential functions.
Unlike vertebrates, which have an internal skeleton (endoskeleton) that supports their bodies from within, mollusks have an exoskeleton that provides structure, protection, and support. The exoskeleton can vary significantly among different mollusk species. For instance, in snails and clams, the exoskeleton manifests as a hard shell that offers protection against predators and environmental hazards.
It’s important to note that some mollusks, like octopuses, do not have a hard shell. Instead, they possess a more flexible form of tissue which allows for greater mobility and adaptability. Despite this, they are still classified as having an exoskeleton due to their evolutionary lineage.
In summary, mollusks are primarily characterized by their exoskeletons, which serve to protect and support their bodies, while variations exist among species regarding the hardness and presence of external shells.