Mollusks are invertebrate animals, that is, they have no spine, they have a long, slimy body. Some species, for example, oysters and shellfish, have a protective shell, while other mollusks, such as octopus and squid, do not.

Division of molluscs – General characteristics


This is the case with mollusks such as snails and some species of slugs. They are mollusks that have contractile tentacles, (which can be collected), and the spiral-shaped shell, used as a form of protection.

Other species, such as slugs, despite not having a shell are classified in the same group. These animals can be aquatic or terrestrial beings. In the case of the terrestrial, it always needs a humid environment and its breathing is carried out by means of lungs, whereas aquatic molluscs carry out their breathing by means of gills.

The head of a gastropod has two pairs of tentacles and its eyes are located at the ends of the longest pair of tentacles.


Photo: Reproduction


Representatives of this class are oysters, mussels and seafood. The shell of this type of mollusk is formed by two valves that can open or close. The molluscs of this classification do not have a defined head and their feet may often not exist or be small (in the shape of a hammer). Bivalves feed on particles transported by water.

Bivalves that have a foot, use it as a way of fixing in the sand, it is called bisso. Their breathing is branchial, and they feed on particles that are trapped in their gills, and through their lashes, these foods are taken to your mouth. They are aquatic animals, and can be found in both seawater and freshwater. Some of its species are capable of producing pearls.

Pearls are formed from some object that enters its shell, so the mollusk creates several layers of nacre. After several insertions of this substance, the pearl forms inside the shell.


In this class we find squid, octopus, nautilus and argonaut, known as marine animals. The molluscs of this classification have no shell, in addition, their eyes are developed and in their tentacles are found several suction cups. Their defense structure is formed by chromatophores, that is, when they feel threatened, they release a pigment that darkens the water around them, confusing predators.

Mollusc reproduction

Mollusks can be hermaphroditic or dioecious, which are:

– Hermaphrodites: mollusks that present both sexes, that is, female and male.
– Dioecious: mollusks in which sex is separated into individuals, that is, male and female.

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