+20 animals with shells

The shell is a support and protection structure that many animals present. Its morphology is highly variable, depending mainly on whether it appears in vertebrate or invertebrate animals.

Internal skeletons

In vertebrate animals, as we well know, we find bony or cartilaginous internal skeletons, divided into trunk and extremities. In this case, the structure of the shell is anchored to the spine and the rib cage of the animal, being one more element of its internal skeleton .

external skeletons

On the other hand, there are external skeletons, which support proportionally less weight than endoskeletons of the same size. The main examples of exoskeleton are found among arthropods (group of invertebrates), in which the exoskeleton forms a shell that protects internal organs. In addition, we can find other ways of naming it, such as shell .

Within the arthropods, the group of crustaceans stands out as carriers of shell or shell in their anatomy. Although they are not the only invertebrates that present it, it is also the case of mollusks.

Let’s take a closer look at these types of shell with some examples.

Whether terrestrial, marine or freshwater, the internal skeleton of turtles develops its own strength as a shell, a unique trait among vertebrates. The shell of these reptiles acts as an envelope that protects the internal organs of their body, allowing the head, the front and rear legs, and the tail to emerge from it.

• Land tortoises: in land tortoises, such as the Mediterranean tortoise ( Testudo hermanni) , the shell is always dome-shaped, to prevent possible predators from catching them with their mouths or claws.
• Sea or freshwater turtles : on the other hand, in aquatic turtles , the shape of the shell is flattened, presenting a more hydrodynamic and lighter structure that allows them to be great swimmers, such as the loggerhead turtle ( Caretta caretta ) and the tortoise. Florida ( Trachemys scripta elegans ).

Mollusks constitute one of the great phyla (Phylum Mollusca) within the animal kingdom. In it, the gastropods (“feet on the stomach”), the bivalves (“two valves”) and the cephalopods (“feet on the head”) stand out.

The soft body of mollusks is protected by a shell formed from cells that secrete calcium carbonate , which crystallizes outside as a calcareous substrate. Thus, a resistant and essential structure is constituted to avoid the dissolution of the organism in acidic environments.

The shell of land and marine snails (Gastropods) is in one piece and is wound in a spiral, being normally open to the right side.

Regarding the group of bivalves, they present a carapace with two symmetrical lateral valves, which are closed by the action of one or two muscles and linkages that act as a hinge. Those commonly known as mussels (Mytilioida family), oysters (Ostreoida family) and clams (Veneroida family) are some of the many examples of marine bivalves.

Among the most surprising mollusks appears the nautilus (genus Nautilus ), a living fossil belonging to the group of cephalopods, whose outer shell is highly developed, flat-spiral and totally septate.

Crustaceans, as arthropods that they are, have an exoskeleton whose main component is chitin . This exoskeleton often acquires the character of a true shell, being mineralized with calcium salts, which gives it great hardness. Among the main crustaceans, we can find:

• Crabs
• Crawfish
• Lobsters
• Lobsters

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