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Mollusks are a class of invertebrates that is made up of animal species characterized by having a soft body and, in most cases, a shell, carapace or exoskeleton that protects them. After arthropods, mollusks form the second largest group of invertebrates, including up to 85,000 different species.
Some species of mollusks live in salt water, others in fresh water, and others are terrestrial animals. All reproduce by sexual reproduction. Some species do so by external fertilization and there are some species that are hermaphrodites, while other species reproduce by internal fertilization. Additionally, they are oviparous.
There are eight different classes of mollusks, which are:
- gastropods
- cephalopods
- bivalves
- scaphopods
- caudofovate solenogastros
- polyplacophorans
- monoplacophores
Some typical examples of these invertebrates are:
- clams
- The different species of octopus
- The squids
- The oysters
- The mussels
- nautilus
- slugs
- The different species of snails
The anatomy of a mollusk
In addition to being invertebrates and having a soft body, the eight classes of mollusks are characterized by having the following characteristics: a muscular foot that is used for locomotion, a circulatory system made up of one or more hearts, an aorta, and a system of blood vessels. Many species of mollusks are protected by a shell or carapace, and all are characterized by having a mantle that covers all the visceral organs. The following image shows the anatomy of a snail, which is representative of mollusks and their anatomy.
This mantle is one of the most important and characteristic anatomical parts of mollusks and can fulfill a series of functions that are vital for their survival, which will be described below.
What is the mantle of mollusks and what is it for?
The mantle of a mollusk forms the external layer of its body and, therefore, encloses the set of internal organs that form the visceral mass. It is a fabric made up of three folds or layers. The outer layer produces the material that forms the shell in some mollusks, the intermediate layer is generally sensory, while the inner layer is muscular. In a few words, it is a muscular organ characteristic of these invertebrates and that has evolved in each species to fulfill different functions.
In many species of mollusks, the mantle is completely hidden within the shells or shells of the animal. However, in other species the mantle extends beyond the edges of the carapace. This protruding part is called the coat flap and sometimes gives the appearance of a cloak or blanket that covers the animal, which is where it gets its name. In addition to being called mantle, this part of the mollusk’s body is also often called pallium or pallium, which is nothing more than the same term in Latin.
Functions of the mantle of mollusks
As mentioned above, the mantle can serve a wide variety of functions for mollusks. The most important and common ones are explained below.
Protects the visceral mass
This is the main function of the mantle. It corresponds to a thick layer of tissue that includes both epithelial tissue and muscle tissue, which serves as a barrier between the environment and the delicate internal organs of the mollusk. We could say that it is the equivalent in molluscs to the skin of vertebrate animals. Although many species of mollusks are also protected by a shell, in some cases the mantle is the only thing that separates the visceral mass from the environment and from predators.
Produces the shells, shells or exoskeletons of some species of mollusks
Even in the cases of species such as oysters, clams and snails, which have a thick external calcareous shell that provides an additional layer of protection, this protection is due to the mantle. This is because, in all these cases, it is the mantle that, through the cells on its surface, secretes calcium carbonate and the other substances that form the matrix of the shell.
Helps in respiration, feeding and excretion
In all mollusks, the mantle encloses a hollow area called the paleal cavity or mantle cavity. This small chamber is normally located at the rear of the animal’s body and contains, among other things, the ctenidia . These are flat organs that serve both for respiration (fulfilling a function similar to the gills) and for the absorption of some nutrients directly from the water.
The paleal cavity also contains the mouth of the digestive system, through which the animal excretes undigested waste from its food. Thanks to the siphon shape and the musculature of the mantle, it helps to make fresh and oxygenated water flow from the outside towards the paleal cavity, bringing oxygen and nutrients so that the ctenidium absorbs them; then it helps to expel the water again, dragging with it the waste excreted by the mollusk.
used for locomotion
As mentioned above, the mantle is a muscular organ. Thanks to this, some species evolved to use the mantle flap as fins that allow them to move in the water.
On the other hand, cephalopods developed the ability to use the mantle as a “jet” propulsion system. To do this, these species of mollusks fill the cavity of the mantle with water and then contract the mantle, expelling the water at high speed through a siphon formed by the mantle itself. This technique is so effective that it is the main form of locomotion for squids, octopuses and other cephalopods, despite the fact that some have tentacles with which they can also move across the surface of the sea floor.
Assist in reproduction
In addition to containing the ctenidium and the mouth of the molluscan anus, the paleal cavity also contains the molluscan gonads. Through the same siphon mechanism that allows the evacuation of the mollusc’s excrement, the mantle also helps in the release of gametes or sexual cells to allow external fertilization in many species of molluscs.
Camouflage and communication
A peculiarity of some species of mollusks, such as the mime octopus, is that on the surface of the mantle they have specialized cells called chromatophores, which are sensitive to light and allow the animal to change color. This gives these species the ability to camouflage and go unnoticed both to defend themselves from predators and to hide and stalk their prey without being detected.
On the other hand, some species have very colorful and already striking mantles that make them useful for communicating with other members of their species.
References
- Encyclopedia of Examples. (2019). molluscs . Examples.co. https://www.examples.co/molluscos/
- Menéndez V., JL, & Lorenzo C., A. (sf). General characteristics of Molluscs . asturnatura.com [online] No. 70. https://www.asturnatura.com/moluscos/caracteristicas-molluscos.html
- molluscs | Introduction | Fish and shellfish . (nd). EROSKI Foundation. https://pescadosymariscos.consumer.es/moluscos/introduccion
- Moreno, AG (sf). Zoology Notes – Molluscs . UCM.es. https://www.ucm.es/data/cont/docs/465-2013-08-22-E1%20MOLUSCOS.pdf
- National Geographic. (2018, August 9). Octopuses talk and fight like this . National Geographic in Spanish. https://www.ngenespanol.com/naturaleza/los-pulpos-hablanasi/
- What is a mantle on the body of a mollusk? – Information – 2021 . (2021). LesKanaris. https://us.leskanaris.com/4290-what-is-a-mantle-in-the-body-of-a-mollusk.html
