Mollusks are classified according to several characteristics, the most important of which is that they contain a shell

Mollusks are classified according to several characteristics, the most important of which is that they contain a shell

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Mollusks are classified according to several characteristics, the most important of which is that they contain a shell

Mollusks are classified according to several characteristics, the most important of which is that they contain a shell. Many people believe that the bodies of all living organisms consist of a skeleton, not that there are some living organisms that do not have a skeleton in their bodies, and this makes them more flexible, and falls under this category. A large number of these species, and they are called mollusks, where mollusks are described as a group of living organisms, which are characterized by their soft bodies, and are mostly covered with a solid structure like shells, and this structure protects them from external factors, so the answer to the questionMollusks are classified according to several characteristics, the most important of which is that they contain a shell correct answer.

What are mollusks?

  • Mollusks are known in English (Mollusk), and mollusks are considered one of the most diverse animals in the world, with no less than 50,000 species and up to 20,000 species.
  • It was believed to have become extinct millions of years ago, but one was discovered in 1952 in the depths of the ocean off the coast of Costa Rica.
  • Mollusks are considered primarily aquatic organisms, as the majority of them live in salt water, and a few live in brackish water and on land.
  • And mollusks can be obtained in a hidden form inside other animals.

What are the characteristics of mollusks?

Mollusks share many characteristics which are as follows:

places to live

Mollusks adapt to live in many different environments, some of them live in the land environment, others live between rock voids, or in sandy areas, and there are some of them live in aquatic environments, and there are no flying mollusks, that is, there are no mollusks that live in the air.

the size

The size of mollusks is that they are very small and minute organisms, with a size of a few millimeters, like the ventricles of the feet, and at some time they reach large sizes that extend to several meters, and the squid is the largest invertebrate creatures.


Mollusks have spread abundantly all over the world, where they have an important biological role, and are an important component of many food chains.

Morphological characteristics of mollusks

  • body shapeMollusks are characterized by a distinctive head with a mouth, eyes, claws, and other sensory organs, and it contains tentacles.
  • the scarfThe mantle that covers the mollusks is what distinguishes them most, as it is the outer covering of them, and the diaphragm of their inner cavity, where the mantle protects the mollusks’ body, and gives them their ability to move and gather food.
  • foot:Mollusks have a distinctive foot that can be moved for use in swimming or crawling.
  • viscous liquid:Mollusks secrete a sticky fluid that they use to defend themselves against predators, and some mollusks secrete harmful chemicals such as toxins, which are secreted from the salivary gland, or unpleasant acids found in the cells of the outer mantle.

types of mollusks

After we have answered the classification of mollusks according to several characteristics, the most important of which is that they contain the shell, we will explain to you the types of mollusks, where mollusks are divided into ten categories, two of which are extinct and the other species are found in several different environments, which are as follows:

  • gastropodsThis type of mollusk is considered one of the most diverse species of mollusk, as it lives in several environments, including salt water, fresh water and dry land, and this type includes snails and snails.
  • Bivalves:This type of mollusk is edible, such as oysters, oysters and mussels. This type of mollusk is famous for not having a head, and it lives in salty and fresh water.
  • Fang-shelled:Where they have long cylindrical shells and models.
  • multi-shell:These mollusks are described as flat slugs, and they live in the tidal waters of rocky coasts all over the world.
  • cephalopods:This species lacks an outer mantle of nacre, such as octopus and squid.
  • plank monocytes: It is found in the depths of the sea, covered with shells, and it was believed that this type of mollusk became extinct, but scientists discovered some of them in 1952.
  • Codophophyta: This type of mollusk is small in size, lives in the depths of the sea, hides in the hall, and looks like worms.
  • Neominimorpha: This type is similar to worms, and lacks shells and lives in the ocean. These mollusks are often blind and either cylindrical or flat in shape.

mollusk food

  • Mollusks are divided into types that feed on meat and other types that feed on plants. Some of them, such as cephalopods and gastropods, feed on crabs, crayfish, small species of mollusks, oysters, crustaceans and shrimp.
  • As for others, such as small squid, they feed on algae phytoplankton mainly, and there is a class of plants that feed on different plants.

mollusk life cycle

The life cycle of mollusks has many distinctive features, as it passes through three stages, which are as follows:

fertilization stage

The first stage begins with the fertilization of eggs inside the female’s body by the male, and the female places her eggs in a safe place, and keeps them. This type of fertilization in the reproduction of oysters.

hatching stage

At this stage, different types of eggs are laid, according to the type of mollusk, and the eggs hatch after a period of two to four weeks, and this period varies according to the type, and then the small larvae appear.

growth stage

Young larvae begin to grow within several weeks, and then become an adult organism capable of mating and fertilization again, and there are some types of mollusks that do not reach sexual maturity, until after some years

The internal composition of mollusks

Mollusks are like other living things, as their bodies consist of many organs, which are as follows:

  • Muscles and tissues:The body of the mollusk includes a group of dorsal ventral muscles that connect the body parts to each other, as these muscles and tissues help them to move, and their bodies are characterized as mollusks filled with tissues and fluids.
  • Nervous system: This system contains a pair of brain ganglia, a pair of collateral nerve cords that emerge from the dorsal brain ganglia, and a ventral pair of nerve cords, and both cords are connected to each other through the lateral branches of nerve fibers.
  • Digestive:Mollusks have a simple digestive system, consisting of a mouth and a posterior anus, except for the gastropods. This type of mollusk has a U-shaped intestine, where the anus is in front, and this indicates that the digestive system of mollusks is in the form Straight, and contains a stomach, digestive gland, and slender intestines.
  • circulatory system:The periodic system of mollusks is characterized by that it is devoid of apparent walls, through which body fluid is transported inside the sinuses, and its heart consists of a ventricle and two hind ears, and mollusks have many gills, and there are some species that live on land that have developed lungs, and thus breathing occurs through the gills or lungs or both. together.
  • Reproductive system: Mollusks are classified into males and females, but sometimes they are hermaphrodites, and fertilization is external or internal, and eggs or sperms are placed in the cavity of the pericardium, which is a thin sac found in their composition, and they move by a method and from here fertilization occurs.

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