What are Molluscs?

Molluscs are a large group of invertebrates that include familiar species such as snails, shellfish, octopuses, and squids. They are one of the most diverse and widespread animal phyla on Earth, living in marine, freshwater, and terrestrial environments.

Key characteristics of molluscs

Molluscs are named for their soft, boneless bodies. Although they vary greatly in appearance and habitat, they share several common characteristics:

1. Soft body: Molluscs have no bones and are usually made up of three parts: a head, a foot, and a visceral mass. They have soft bodies, and many species rely on shells for protection.

2. Shell protection: Many mollusks, such as clams and snails, have hard shells made of calcium carbonate to protect their soft bodies. However, some species, such as octopuses and squids, do not have shells and have evolved other defense mechanisms.

3. Foot: Most species of mollusks have muscular feet for locomotion. Snails use their feet to move slowly on the ground or underwater, while squids and octopuses use specialized foot structures to jet and swim quickly.

4. Gills or lungs: Most mollusks that live in water breathe through gills, while species that live on land, such as land snails, use lungs.

5. Open circulatory system: Molluscs usually have an open circulatory system, with blood flowing through blood vessels and body cavities in the animal's body. A few mollusks, such as cephalopods (octopuses, squids), have a closed circulatory system, with blood flowing only in blood vessels.

Classification of Molluscs

The phylum Molluscs contains several important classes, the most common of which are the following:

1. Gastropoda

• Representative species: snails, slugs

• Characteristics: Gastropods are the most diverse group of molluscs, with a wide distribution, including marine, freshwater, and terrestrial species. They usually have a spiral shell, although some species (such as slugs) do not have a shell.

2. Bivalvia

• Representative species: clams, oysters, mussels, scallops

• Characteristics: Bivalve molluscs have a body surrounded by two hard shells connected by hinges. They mainly live in marine and freshwater, relying on gills to filter tiny food in the water.

3. Cephalopoda

• Representative species: octopus, squid, cuttlefish, nautilus

• Characteristics: Cephalopoda is the most complex mollusk, with a developed nervous system and visual organs. Their feet have evolved into tentacles to catch prey. Many cephalopods can spray ink for self-defense and change color through pigment cells for camouflage or communication.

4. Polyplacophora

• Representative species: Chiton

• Characteristics: The back of the Polyplacophora molluscs is covered by a series of eight overlapping hard plates. They live on the rocky surface of the ocean and mainly feed on algae.

5. Scaphopoda

• Representative species: Ivory snail

• Features: Scaphopoda mollusks are usually tubular, with ivory-like shells buried in the seabed. They use their tentacles to capture tiny food particles.

Ecological Role of Molluscs

Molluscs play an important role in the ecosystem:

1. Food Source: They are an important food source for many marine organisms (such as fish and seabirds), and are also important seafood resources for humans, such as oysters, clams and squid.

2. Ecological Balance: Bivalve animals help keep water clean by filtering organic particles in the water. Gastropod species play an important role in decomposing organic matter and regulating the growth of algae.

3. Bioengineer: Some mollusks, especially oysters and mussels, provide habitats and shelters by building reefs or attaching to other objects, promoting ecological diversity.

Economic and Cultural Value of Molluscs

Molluscs have significant economic value in human society. They are an important part of the seafood industry, and clams, oysters, mussels, octopus, and squid are common ingredients on people's tables. In addition, mollusc shells are often used as decorations, currency, or other cultural symbols. Pearls come from mollusks such as oysters and mussels, and their value in the jewelry industry is immeasurable.

Conclusion

Molluscs are one of the most diverse animals on Earth, covering a wide range of ecological environments from the ocean to the land. Whether it is their unique physiological structure, important ecological role, or economic value, they occupy an indispensable position in humans and nature. As we further study mollusks, we will better understand these amazing creatures and their contributions to global ecosystems.

The following is an inventory of common mollusks, presented in a table and organized by classification class:

This table lists representative species of the phylum Mollusca and their main characteristics. These species are widely distributed in different environments, from marine to terrestrial, demonstrating the diversity and adaptability of mollusks.

animal tags： Molluscs