Animals with hard shells are commonly referred to as molluscs or shellfish. Molluscs are a diverse group of animals that belong to the phylum Mollusca, which is one of the largest phyla in the animal kingdom. They are characterized by their soft bodies and the presence of a hard shell that provides them with protection.
The term “shellfish” is often used to describe molluscs because many species within this group have shells. However, it is important to note that not all molluscs have shells, and not all shellfish are molluscs. For example, crustaceans such as crabs and lobsters also have hard shells but belong to a different phylum.
Molluscs can be found in various habitats, including the ocean, freshwater, and even on land. The majority of molluscs are marine species, with approximately 100,000 known species worldwide. They inhabit a wide range of environments, from shallow coastal waters to the deep sea.
The shells of molluscs are composed primarily of calcium carbonate, which is secreted by a specialized tissue called the mantle. The mantle covers the soft body of the mollusc and continuously produces new shell material as the animal grows. The shape and size of the shell vary greatly among different species of molluscs.
Molluscs have evolved shells for several reasons. One of the main functions of the shell is protection against predators and physical damage. The hard exterior provides a barrier between the mollusc’s vulnerable body and the surrounding environment. Some molluscs have elaborate and intricately patterned shells, which may also serve as a form of camouflage or a means of attracting mates.
It is worth mentioning that the term “shellfish” is often used more broadly to include other animals with hard shells, such as crustaceans and certain types of echinoderms. Crustaceans, which include crabs, lobsters, and shrimp, have an exoskeleton made of chitin, a tough and flexible material. Echinoderms, such as sea urchins and starfish, have a calcareous endoskeleton composed of plates or spines.
Animals with hard shells are commonly called molluscs or shellfish. Molluscs are a diverse group of animals with soft bodies and hard shells, while shellfish may also include other types of animals with hard shells, such as crustaceans and echinoderms. The shells of molluscs serve as protection and can exhibit a wide range of shapes, sizes, and patterns.