A mussel is a bivalve mollusk found worldwide, especially in cooler seas. Marine mussels are typically wedge or pear-shaped, ranging from 2 to 6 inches in size, with smooth or ribbed shells that are often dark blue or greenish-brown. Mussels attach to solid surfaces using byssus threads and are frequently found in dense clusters. Some species burrow in mud or wood. They are filter feeders that strain food particles from the water. Certain mussel species, such as the blue mussel, are commercially cultivated as a food source, while others, like the zebra mussel, are considered pests due to their ability to clog water pipes and disrupt aquatic ecosystems.

How are mussels different from other types of mollusks?

Mussels are bivalve mollusks, meaning their bodies are enclosed in a two-valved shell. They belong to the families Mytilidae (marine) and Unionidae (freshwater) and are common worldwide, especially in cooler seas. Mollusks are a diverse group of soft-bodied invertebrates, typically enclosed in a calcium carbonate shell. Mussels attach to solid objects using byssus threads, often forming dense clusters, while other mollusks exhibit diverse lifestyles and adaptations. For example, some mollusks like squids , octopuses , and nautiluses (all cephalopods) possess arms or tentacles and are free-swimming. Other bivalves can burrow, and some have adapted to carnivory.

Where do mussels usually live?

Mussels are bivalve mollusks found worldwide, particularly in cool seas and freshwater habitats like streams, lakes, and ponds. Marine mussels commonly appear in wedge or pear shapes, attaching to solid surfaces or each other using byssus threads, often forming dense clusters. Some species can burrow into soft mud or wood. Freshwater mussels, such as the zebra mussel, can attach to almost any surface.

How do mussels eat and breathe underwater?

Mussels are filter feeders that use their gills to strain food particles from the water. Cilia, or microscopic whips, produce a water current over the gills, and other cilia move the trapped food particles along the gill face and into food grooves. The labial palps then process this food. Mussels breathe using gills that facilitate gas exchange between water and blood. Water circulates across the gills, and oxygen is extracted. The currents produced by ciliary movement ventilate and bring in food. Mussels can close their shells to prevent dehydration during low tide, switching to anaerobic metabolism until normal conditions return.

What role do mussels play in their ecosystem?

Mussels play a significant role in their ecosystems, both in marine and freshwater environments. As filter feeders, mussels filter water to obtain food, which helps maintain water quality. This filtering activity can affect the populations of invertebrate larvae in the water. However, mussels can also disrupt ecosystems. For example, the zebra mussel is known to wipe out phytoplankton, which disrupts the aquatic food chain and threatens native mussel species. They can also cause commercial damage by clogging water pipes and other structures. Mussels also serve as a food source for various animals, including birds and starfishes. Some mussel species, like the blue mussel, are commercially cultivated and consumed by humans.

How are mussels important to humans and the environment?

Mussels play a significant role for both humans and the environment. As filter feeders, mussels contribute to the organic turnover in marine and fresh water by filtering up to 40 liters of water per hour. Certain mussel species, such as the blue mussel , are important as food sources and are raised commercially in Europe and other parts of the world. However, mussels can also have negative impacts. For example, the zebra mussel is considered a harmful exotic invader that clogs water pipes and outcompetes native mussel species, disrupting the aquatic food chain.

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Images & Videos

The video thumbnail image shows two hands holding zebra and quagga mussels, superimposed above a clear body of water. White question marks appear in the upper left corner.

A boat propeller encrusted with zebra mussels against a white background.

Oysters, clams and mussels arranged on crushed ice with clearly visible price tag at a seafood market.

Discover an undersea cluster of mussels and alvinocaridid shrimp found at NW Eifuku located near the Mariana Islands

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Related Topics:: bivalve; aquaculture; What’s the difference between clams, mussels, and oysters?; freshwater mussel; marine mussel

On the Web:: PNAS - Invasive mussels regulate nutrient cycling in the largest freshwater ecosystem on Earth (Oct. 27, 2026)

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Top Questions

What is a mussel?
A mussel is a bivalve mollusk found worldwide, especially in cooler seas. Marine mussels are typically wedge or pear-shaped, ranging from 2 to 6 inches in size, with smooth or ribbed shells that are often dark blue or greenish-brown.

Mussels attach to solid surfaces using byssus threads and are frequently found in dense clusters. Some species burrow in mud or wood. They are filter feeders that strain food particles from the water.

Certain mussel species, such as the blue mussel, are commercially cultivated as a food source, while others, like the zebra mussel, are considered pests due to their ability to clog water pipes and disrupt aquatic ecosystems.
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How are mussels different from other types of mollusks?
Mussels are bivalve mollusks, meaning their bodies are enclosed in a two-valved shell. They belong to the families Mytilidae (marine) and Unionidae (freshwater) and are common worldwide, especially in cooler seas. Mollusks are a diverse group of soft-bodied invertebrates, typically enclosed in a calcium carbonate shell.

Mussels attach to solid objects using byssus threads, often forming dense clusters, while other mollusks exhibit diverse lifestyles and adaptations. For example, some mollusks like squids, octopuses, and nautiluses (all cephalopods) possess arms or tentacles and are free-swimming. Other bivalves can burrow, and some have adapted to carnivory.
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Where do mussels usually live?
Mussels are bivalve mollusks found worldwide, particularly in cool seas and freshwater habitats like streams, lakes, and ponds. Marine mussels commonly appear in wedge or pear shapes, attaching to solid surfaces or each other using byssus threads, often forming dense clusters. Some species can burrow into soft mud or wood. Freshwater mussels, such as the zebra mussel, can attach to almost any surface.
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Created from Britannica articles using AI. AI can make mistakes, so verify using Britannica articles.
How do mussels eat and breathe underwater?
Mussels are filter feeders that use their gills to strain food particles from the water. Cilia, or microscopic whips, produce a water current over the gills, and other cilia move the trapped food particles along the gill face and into food grooves. The labial palps then process this food.

Mussels breathe using gills that facilitate gas exchange between water and blood. Water circulates across the gills, and oxygen is extracted. The currents produced by ciliary movement ventilate and bring in food. Mussels can close their shells to prevent dehydration during low tide, switching to anaerobic metabolism until normal conditions return.
6 Britannica Sources
Created from Britannica articles using AI. AI can make mistakes, so verify using Britannica articles.
What role do mussels play in their ecosystem?
Mussels play a significant role in their ecosystems, both in marine and freshwater environments. As filter feeders, mussels filter water to obtain food, which helps maintain water quality. This filtering activity can affect the populations of invertebrate larvae in the water.

However, mussels can also disrupt ecosystems. For example, the zebra mussel is known to wipe out phytoplankton, which disrupts the aquatic food chain and threatens native mussel species. They can also cause commercial damage by clogging water pipes and other structures.

Mussels also serve as a food source for various animals, including birds and starfishes. Some mussel species, like the blue mussel, are commercially cultivated and consumed by humans.
6 Britannica Sources
Created from Britannica articles using AI. AI can make mistakes, so verify using Britannica articles.
How are mussels important to humans and the environment?
Mussels play a significant role for both humans and the environment. As filter feeders, mussels contribute to the organic turnover in marine and fresh water by filtering up to 40 liters of water per hour. Certain mussel species, such as the blue mussel, are important as food sources and are raised commercially in Europe and other parts of the world.

However, mussels can also have negative impacts. For example, the zebra mussel is considered a harmful exotic invader that clogs water pipes and outcompetes native mussel species, disrupting the aquatic food chain.
3 Britannica Sources
Created from Britannica articles using AI. AI can make mistakes, so verify using Britannica articles.

mussel, any of numerous bivalve mollusks belonging to the marine family Mytilidae and to the freshwater family Unionidae. Worldwide in distribution, they are most common in cool seas. Freshwater mussels, also known as naiads, include about 1,000 known species inhabiting streams, lakes, and ponds over most of the world.

Marine mussels are usually wedge-shaped or pear-shaped and range in size from about 5 to 15 centimetres (about 2 to 6 inches). They may be smooth or ribbed and often have a hairy covering. The shells of many species are dark blue or dark greenish brown on the outside; on the inside they are often pearly. Mussels attach themselves to solid objects or to one another by proteinaceous threads called byssus threads; they often occur in dense clusters. Some burrow into soft mud or wood. Principal enemies of the mussel are birds (e.g., herring gulls, oystercatchers, ducks), starfishes, and dog whelks.

Some species (e.g., the blue mussel, Mytilus edulis) are important as food in Europe and other parts of the world and are raised commercially. M. edulis, which attains lengths of up to 11 cm and is usually blue or purple, has been cultivated in Europe since the 13th century. Mussels are collected from deep water by means of dredges or rakes.

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The two species of the tiny zebra mussel (genus Dreissena) are prominent freshwater pests, known to proliferate readily and to adhere in great numbers to virtually any surface. The zebra mussel’s filtering activities tend to wipe out phytoplankton, disrupting the aquatic food chain that supports many fish species and driving many native mussel species to extinction. In addition, its massive clustering on water-intake valves and pipes, bridge abutments, and other structures can cause severe commercial damage. The zebra mussel made its first known attack on Europe in the early 1800s, proliferated in the 20th century, and was carried (probably in ship ballast water) to North America about 1986, eventually invading all the Great Lakes. At present, zebra mussels are spreading to inland lakes and other waterways in parts of the United States.

The capax horse mussel (Modiolus capax) has a bright orange-brown shell under a thick periostracum; its range in the Pacific Ocean extends from California to Peru. The Atlantic ribbed mussel (Modiolus demissus), which has a thin, strong, yellowish brown shell, occurs from Nova Scotia to the Gulf of Mexico. The tulip mussel (Modiolus americanus), from North Carolina to the Caribbean Sea, attaches itself to broken shells and rocks; its smooth, thin shell is usually light brown but sometimes has rosy or purple rays.

The yellow mussel (Mytilus citrinus), from southern Florida to the Caribbean, is a light brownish yellow. The hooked, or bent, mussel (M. recurvus), from New England to the Caribbean, attains lengths of about 4 cm and is greenish brown to purplish black. The scorched mussel (M. exustus), from North Carolina to the Caribbean, is bluish gray and about 2.5 cm long.

The largest family of freshwater mussels is the Unionidae, with about 750 species, the greatest number of which occur in the United States. Many unionid species also live in Southeast Asian waters. Several North American unionids are threatened by habitat degradation, damming, and the invasion of zebra mussels.

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