Mollusca is a broad phylum of invertebrate animals having a soft body of bilateral symmetry. they have muscular feet covered by their bodies protected by a shell or calcium-based exoskeleton except for octopuses. All Molluscs are considered aquatic animals, having more than 100,000 species.
they are said to be the second-largest phylum in the animal kingdom after the arthropods.
This is a Complete Guide About Phylum Mollusca Characteristics.
- What is Mollusca (Definition)
- Some Examples of Mollusca
- Mollusca Nervous system
- Mollusca Digestive System
- Mollusca Respiratory System
Common name, habitat, classes, and more….!
Let’s get started.
What is Phylum Mollusca?
Mollusca is considered the second-largest phylum of animals after Arthropoda and is an invertebrate. they have a foot along with a ventricle structure for locomotion. An open circulatory system is present in some mollusks for the blood circulation through vessels and also some have closed circulatory systems to move blood through the body enclosed entirely in blood vessels.
General Characteristics of Phylum Mollusca
The phylum Mollusca is composed of a variety of organisms. They include slow-moving snails and slugs bivalved (shell with two parts) clams and highly active cephalopods. This phylum has 50,000 living species. It is the second-largest phylum of invertebrates. The giant squid is the largest invertebrate animal.
Mollusks show a great variety of forms (structures). But all Molluscs have the same basic structure. They show the following characters:
- Body Characters: They are triploblastic, coelomate, and show bilateral symmetry.
- Mantle and shell: The body is covered by a glandular (having glands) epithelial envelope called the mantle. It secretes a calcareous shell. The shell is a protective structure. However, it slows down the locomotion. So some of the active Molluscs have reduced or lost their shell.
- Habitat: They are widely distributed. Some groups are exclusively aquatic, freshwater, or marine (e.g. Cephalopoda). The other Molluscs are terrestrial animals (e.g. Land snails). They live in moist places.
- Body structure: They have an unsegmented and soft body. The body can be divided into:
- A ventral muscular foot
- Dorsal visceral mass, containing most of the internal organs.
The mantle is present over the visceral mass. Mantle secretes outer shell. The space between the shell and the mantle cavity contains gills in some Molluscs. A rasping tongue-like structure radula is present in the mouth cavity of many Molluscs. The radula has many horny teeth. The body is highly organized. It has complex digestive, respiratory, circulatory, excretory, nervous, and reproductive systems.
- Digestive system: The digestive system consists of the gut. It has two openings, a mouth, and an anus.
- Excretory system: The excretory organs are paired with nephridia.
- Circulatory system: They have an open circulatory system, except Cephalopoda. The coelom is divided into sinuses or blood spaces.
The heart pumps blood into these sinuses. They have a blue respiratory pigment called hemocyanin.
- Respiratory system: The exchange of gases takes place by gills. In some cases like snails, the mantle cavity is converted into lungs.
- Nervous system: The nervous system consists of three pairs of interconnected ganglia. These ganglia are present in the head, foot, and body regions.
- Locomotion: The organ of locomotion is the muscular foot. Movement is slow in many species. The other Molluscs are sessile i.e. unable to move.
- Reproduction: The sexes are separate. They develop trochophore larva during their development.
Examples of Phylum Mollusca
- Sea hare
Classification of Phylum Mollusca
The Molluscs are divided into three classes. There following major classes:
- Their body is asymmetrical (without any symmetry). Their body is covered with coiled shell. The animal can withdraw itself into the shell.
- They are both aquatic and terrestrial.
- The aquatic species have lungs. While in terrestrial animals the mantle cavity is converted into lungs.
- They have bilateral symmetry with a dorso-ventrally body.
- All species are aquatic.
- The shell is much reduced and internal. In most cases, it is absent.
- These animals are highly developed and active.
- Loligo: Squid
- Sepia: Cuttle Fish
Economic Importance of Mollusca
Mollusks are indirectly harmful to man. The harmful Molluscs are slugs and shipworms.
- Slug: They are harmful to gardens and other cultivations. They eat leaves and destroy plants by cutting up their roots and stems.
- Teredo (Shipworm): It damages wooden parts of ships.
Most Molluscs are beneficial.
- Many types of Molluscs are used as foods by man. A large number of clams, oysters (cf), and mussels are eaten in the Far East (Japan, China), Europe, and America. Oysters are regarded as delicious food.
- Shells of freshwater mussels are used in the button industry.
- Shells of oysters are mixed with tar for making roads in America.
- Their shells are used for making ornaments in certain countries.
- Some oysters make valuable pearls. For Example Pearl Oyster.
Other Related Phyla:
- Phylum Porifera Characteristics & Examples
- Phylum Chordata Characteristics & Classification
- Characteristics of Phylum Echinodermata
- Phylum Coelenterata/Cnidaria Characteristics and Examples
- Phylum Porifera/Sponges With Examples & Characteristics
- Phylum Protozoa: Characteristics & Groups/Classes