Animals in the phylum Mollusca generally have exoskeletons. Most mollusks, such as snails, clams, and squids, are known for their hard shells, which serve as a protective outer structure.
The exoskeleton of mollusks is primarily made of calcium carbonate, which provides strength and durability. This hard shell is not only a defense mechanism against predators but also helps to prevent water loss in land-dwelling mollusks. In contrast to an endoskeleton, which is internal and found in animals like mammals and birds, the exoskeleton of mollusks is external and varies greatly in shape and size across different species.
However, it’s important to note that while many mollusks have a prominent shell, some, like octopuses and squids, have reduced or absent shells. These species still lack an endoskeleton and instead have a soft body, supported by a hydrostatic skeleton, which relies on water pressure within their body for structure.