Phylum Mollusca: Definition, Characteristics, Classification, Exampales
Molluscs are a huge class of soft-bodied invertebrates of the phylum Mollusca, which is one of the largest phyla of the kingdom of animals. Scientists have found over 85,000 different species of molluscs inhabiting freshwater as well as seas. They have a soft, unsegmented body and a hard calcareous shell for protection. They include snails, clams, octopuses, and squids.
This Story also Contains
- What are molluscs?
- General Characteristics of Mollusca
- Classification of Mollusca
- Mollusca Examples
- Recommended video for "Mollusca"
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Molluscs have a small but robust body plan with a muscle tissue foot for the purpose of movement, a mantle to usually forms the shell, and an internal visceral mass housing organs. They have a complete digestive system and a simple circulatory system, except in cephalopods such as octopuses that have a closed circulatory system. Molluscs play an important role in life in nature as grazers, filter feeders, and even predators in various habitats.
What are molluscs?
Molluscs are soft-bodied creatures in the phylum Mollusca, which are present in oceans, freshwater, and terrestrial habitats. They have a hard calcium carbonate-based shell, although there are some groups, such as octopuses and slugs, that do not possess a shell. Molluscs have simple body structures such as a head, foot, and visceral mass. They are ecologically important in ecosystems as grazers, filter feeders, or predators, and they constitute one of the world's largest groups of animals. Some basic points are discussed below:
- Molluscs have a soft and non-segmented body that is usually covered by a shell.
- The body is organised into head, foot, and visceral mass.
- The mantle is a sheet of tissue that aids in the development of the shell in most molluscs.
- Bilateral symmetry is displayed in the body structure of molluscs.
- They have a full digestive system with mouth and anus.
- Most molluscs utilise a radula (toothed organ) to feed.
- They are in marine, freshwater, as well as terrestrial environments.
- Animals such as snails, clams, squids, and octopuses are molluscs.
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General Characteristics of Mollusca
Mollusca is a vast phylum of soft, unsegmented-body animals that are usually covered by a calcium carbonate shell. Their body is divided into three distinct parts: a head for feeding and sensing, a foot of muscle to move, and a visceral mass containing internal organs. Molluscs have a mantle that can secrete a shell and a radula (present in most molluscs) for scraping food. They have bilateral symmetry and a complete alimentary system. Molluscs inhabit marine, freshwater, and terrestrial environments, and most have gills to breathe underwater. The characteristics are described below-
| Feature | Description |
|---|---|
| Soft-bodied animals |
|
| Body structure | The body is divided into head, foot, and visceral mass.
|
| Mantle and shell |
|
| Symmetry | Molluscs have bilateral symmetry, meaning the body can be split into two halves. |
| Body plan | Body form is versatile and varies in shape and function based on the environment. |
Classification of Mollusca
Mollusca is a vast phylum separated into various classes according to body structure, whether they have a shell or not, and habit. Some of the main classes are Gastropoda (snails and slugs), Bivalvia (clams, oysters), Cephalopoda (squids, octopuses), Polyplacophora (chitons), and Scaphopoda (tusk shells). Each class exhibits distinct characters such as torsion in gastropods, hinged shells in bivalves, or tentacles in cephalopods. Molluscs inhabit marine, freshwater, and land habitats.
The characteristics of all of them are listed below-
| Class | Characteristics | Examples |
|---|---|---|
| Gastropoda |
| Helix aspersa (garden snail), Strombus gigas (queen conch) |
| Bivalvia |
| Crassostrea virginica (oyster), Mercenaria mercenaria (clam) |
| Cephalopoda |
| Enteroctopus dofleini (giant Pacific octopus), common squid |
| Polyplacophora |
| Tonicella lineata (lined chiton) |
| Scaphopoda |
| Dentalium entalis (tusk shell) |
Mollusca Examples
Following are a few examples of the phylum Mollusca:
- Turbinella (Shankha)
- Loligo (Squid)
- Limax (Slug)
- Unio (Freshwater mussel)
- Pila (Apple snail)
- Helix (Garden snail)
- Octopus (Devilfish)
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Frequently Asked Questions (FAQs)
It includes soft body tissues usually enclosed in a shell, a head, a foot, a mass of viscera, a mantle that secretes shells in the shelled species and a radula for feeding.
Depending on the structures and life cycles, molluscs are divided into Gastropoda, Bivalvia, Cephalopoda, Polyplacophora, and Scaphopoda.
Molluscs form the basis of fisheries and aquaculture industry particularly clams and oysters since some of them produce pearls, and also useful in biomedical sciences, because of their complicated nervous systems.
Molluscs respond through growth modifications which include shell diversification and feed specialisation which comprise filter feeding, herbivores, and predators as well as burrowing, ability to camouflage and tolerability to extreme climatic conditions.
They consist of the preservation of the species' natural environment, counting populations, breeding in captivity and raising awareness to counter factors that threaten the existence of endangered species and thus total bio-diversity.
