Phylum Mollusca: Characteristics, Uses and Functions

Following Arthropoda, Molluscs remains the world’s largest phylum of invertebrates. Molluscs or molluscs were the members collectively referred to as. Molluscs are thought to comprise about 85000 species. Around 60,000 to 100,000 more species are believed to occur in fossil form. There are a lot of creatures that haven’t been discovered, yet numerous genera remain unclear. Molluscs are derived from the Latin word “mollusc”, which means” soft” and it was initially used by French Zoologist Cuvier around 1798 to denote squids and cuttlefish; these have an internal or lacking shell. Later, the ties among these creatures and other molluscs like snails and bivalves got noticed.

Characteristics

Mollusca have a soft body, which is differentiated into three regions – head visceral hump and foot. The visceral hump is covered by a thin fleshy fold called mantle or palladium. The mouth contains a rasping organ called radula with a file-like transverse row of chitinous teeth.

The muscular foot is utilized for moving as well as several other functions. The mantle is the tissue wrap that encases the body and can hide the shell. The gill or lungs are placed in the mantle cavity. Certain molluscs such as stupid have a calcified shell, while few others like slugs, nudibranchs and octopuses have neither. Phylum Mollusca features are predominantly marine, with some terrestrial and aquatic species.

These could be discovered in the interiors of certain other species as holstered parasites. Molluscs vary significantly in size ranging from massive squids and mussels to a millimeter of snails. 

Classification of Phylum Mollusca

Molluscs are categorized into six diverse classes depending on their symmetry, shells, coating, gills, nervous system and several other traits. 

Class 1 Monoplacophora

Monoplacophora is Dustin given such as they might have a diverse range of critical characteristics. Individuals have associated numerous organs with the sole, shielded shell, implying a minimum partitioning. These were the group of molluscs with a sole cap-shaped casing and bilateral symmetry. Examples of Monoplacophora are Bivalvia, snails, Teuthida and Scaphopoda.

Class 2 Amphineura

Amphineura is a group of elongated, bilaterally symmetrical aquatic creatures. The head is minimally distinguished and a few have stronger radula. It has a frontal shell composed of eight discrete shell layers or hinges. These could be seen in cool, hot and tropical water across the globe. It tends to dwell on or underneath the rock. The Caribbean islands, the Philippines and native Americans from northern and southern America ingest it. A few examples of Amphineura are chitons, neomenia and chaetoderma.Amphineura have two subclasses-

Subclass 1 Aplacophora

Aplacophora is tiny cylindrical. In appearance, they reflect like worms 1mm to 30cm in length. They don’t have a protecting coating like other Mollusca. However, the epidermis emits calcareous spicules or scales implanted in the lateral mantle. The Aplacophorans have a gloss due to their nodules. Examples of Aplacophora are neomenia and  squids .

Subclass-2 Polyplacophora

The body is flat dorso-ventrally, and the head region is tiny without eyes or tentacles. External gills, radula and mantle were seen.Example -Chiton

Class 3 Scaphopoda

Scaphopoda has an elongated body, and they are cylindrical. The feet are conical in shape and meant for dragging and burrowing. They do not have eyes but have tentacles.Example- Tusk shell

Class 4 Gastropoda

They have an asymmetrical body and a distinct head that bears eyes and tentacles. The foot is muscular and broader.It includes the largest number of molluscs.Example- Pila,Garden snail,Sea lemon etc.

Class 5 Pelecypoda

Pelecypoda, we’re the burrowing molluscs. The body is laterally concise. Examples of this species arePearl oysters and clams.

Class 6 Cephalopoda

These species have bilaterally symmetrical bodies where the head region is larger along with a mouth and paired eye. They have fully developed visceral mass. A few Mollusca examples under this class are Loligo and octopus.

Feeding habits of Molluscs

The majority of molluscs are herbivores that eat algae or filter feeds. These are two major dietary options for those that eat. Few consume tiny filamentous algae and use its radula like a scraper to gather filaments from the sea bed.

Plants, fungus and algae were eaten by terrestrial gastropods such as snails and slugs, whereas the vast of aquatic molluscs ingest the soluble plant debris that they filter feed.

Habitat of Molluscs

• They have adapted to a broad range of habitats like terrestrial, marine, benthic and accomplished swimmers.
• Molluscs were developed in the sea region and almost all molluscs were aquatic.
• Few gastropods and bivalves live in freshwater.
• Slugs and snails were terrestrial.

Uses of molluscs

• It is consumed as food mussels, clams, oyster, Avalon’s calamari (squid), octopus, escargot( snails) etc.
• Pearls are made in oysters and clams
• The inner region of shiny shells is used to make buttons.

Internal structure and functions

• Most molluscs have an open circulatory system with a heart, blood vessels and blood sinuses.
• Most Cephalopods have a closed circulatory system with the heart, blood vessels and capillaries.
• The majority of molluscs were unisexual and a few were hermaphroditic.
• Most molluscs’ life cycles have a free-swimming stage, affiliated stage and larval stage.

Conclusion

They are mantle and radial. The mantle is a tissue layer seen around the shell and body. The radula is utilized for drilling holes on the prey.

Phylum Mollusca is fundamentally significant as a component of food chains and environments. Numerous gastropods, bivalves and cephalopods were fed for multiple civilizations and therefore perform a substantial role in most countries fisheries.