Shorelines, estuaries, and freshwater beds host a surprising variety of two-shelled mollusks that quietly shape ecosystems and fisheries. Whether you walk a tidal flat or peer into a clear stream, bivalves can tell you a lot about water quality, habitat type, and regional biodiversity.
There are 20 Bivalve Examples, ranging from Asian clam to Zebra mussel. For each entry, you’ll find below the Scientific name, Habitat, Size (cm) so you can compare where each species lives and how large it typically grows — helpful whether you’re studying, surveying, or just curious about local wildlife; you’ll find the details below.
How can I identify common bivalves in the field?
Look at shell shape, hinge structure, surface texture, and size, and note the habitat (freshwater vs. marine, sediment type). Carry a simple field guide or take clear photos of both valves and the hinge area; comparing those to the Scientific name entries below will quickly narrow possibilities.
Which of these bivalves are likely to be invasive or impact local ecosystems?
Species like the Zebra mussel are notorious invaders that attach to hard surfaces and alter food webs, while others (e.g., Asian clam) can spread quickly in disturbed waters; check the Habitat and regional reports below to see which species are nonnative or monitored locally.
Bivalve Examples
| Name | Scientific name | Habitat | Size (cm) |
|---|---|---|---|
| Eastern oyster | Crassostrea virginica | Estuarine and coastal Atlantic (North America) | 10–15 |
| Pacific oyster | Crassostrea gigas | Temperate Pacific coasts, introduced worldwide | 10–20 |
| Blue mussel | Mytilus edulis | North Atlantic intertidal and subtidal zones | 4–10 |
| California mussel | Mytilus californianus | NE Pacific rocky intertidal (California to Alaska) | 6–15 |
| Zebra mussel | Dreissena polymorpha | Freshwater lakes and rivers (Europe native, invasive N. America) | 1–4 |
| Quahog (hard clam) | Mercenaria mercenaria | Coastal estuaries and sandy bays (Atlantic N. America) | 5–13 |
| Soft-shell clam (steamer) | Mya arenaria | Intertidal mudflats and sandy bays (Atlantic, introduced worldwide) | 4–10 |
| Pacific razor clam | Siliqua patula | Sandy intertidal beaches of NE Pacific | 15–20 |
| Geoduck | Panopea generosa | Subtidal muddy bottoms, NE Pacific | 15–20 |
| Atlantic sea scallop | Placopecten magellanicus | Continental shelf bottoms, NW Atlantic | 8–15 |
| Giant clam | Tridacna gigas | Indo-Pacific coral reefs and lagoons | 60–100 |
| Shipworm | Teredo navalis | Marine wood in warm temperate/tropical coastal waters worldwide | 10–30 |
| Common cockle | Cerastoderma edule | Sandy and muddy intertidal zones, NE Atlantic | 3–6 |
| Fan mussel (pen shell) | Pinna nobilis | Mediterranean sublittoral seagrass beds | 20–50 |
| Freshwater pearl mussel | Margaritifera margaritifera | Cold, well-oxygenated rivers in Europe and N. America | 6–12 |
| Asian clam | Corbicula fluminea | Freshwater rivers and lakes, native Asia, invasive worldwide | 2–5 |
| Manila clam | Ruditapes philippinarum | Coastal sandy/muddy substrates, native NW Pacific, widely cultured | 4–6 |
| Atlantic surf clam | Spisula solidissima | Sandy continental shelf bottoms, NW Atlantic | 10–20 |
| Horse mussel | Modiolus modiolus | Cold temperate subtidal beds, NE Atlantic and Arctic | 6–12 |
| Pismo clam | Tivela stultorum | Sandy beaches of the Eastern Pacific (California coastline) | 7–12 |
Images and Descriptions
Eastern oyster
Briny, irregular-shelled bivalve found on tidal reefs and farms; identifiable by rough, layered shell. Widely eaten raw or cooked and heavily cultured, important for water filtration and estuary habitat restoration.
Pacific oyster
Cupped oyster with fluted shell, farmed globally for aquaculture. Fast-growing and hardy, it dominates commercial oyster production and can be invasive where introduced, altering local ecosystems.
Blue mussel
Dark blue-black mussel forming dense beds on rocks and piers. Commonly harvested for food, easy to spot by byssal threads and triangular shells; important for coastal ecology and filter-feeding water quality.
California mussel
Large, ribbed blue-black mussel clinging to wave-battered rocks. Tough shell and strong byssal threads distinguish it; harvested locally and ecologically important as a foundation species on rocky shores.
Zebra mussel
Small, striped freshwater invader that attaches to hard surfaces in dense colonies. Clogs pipes and alters ecosystems; identifiable by D-shaped shell and zebra-like striping, a major conservation and management concern.
Quahog (hard clam)
Thick-shelled, round clam often called quahog or chowder clam. Valued for chowders and clams on the half shell; shell color varies and growth rings can indicate age and size.
Soft-shell clam (steamer)
Elongated, fragile shell and large burrowing siphons; prized steamed or in chowders. Easily dug from sand; soft shell and gape when alive distinguish it from hard clams.
Pacific razor clam
Long, razor-shaped shell that lives deep in sand. Famous for surf-digging fisheries on Pacific beaches; large siphon and ability to dig rapidly are key ID features.
Geoduck
Huge, elongated-siphoned clam with relatively small shell and very long neck. Prized in Asian markets and farmed; notable for longevity and enormous siphon extending well beyond the shell.
Atlantic sea scallop
Round, ridged scallop with large adductor muscle; swims by clapping valves. Commercially valuable for “scallop” meat; shells often fan-shaped with radiating ribs for identification.
Giant clam
Massive, colorful reef clam with symbiotic algae in its tissues. Highly distinctive for size and bright mantle patterns; protected in many areas due to overharvesting and aquarium trade pressure.
Shipworm
Elongated, worm-like bivalve that bores into submerged wood, causing ship and dock damage. Despite name, it’s a bivalve with tiny shell plates; ecologically important decomposer and notorious pest historically.
Common cockle
Small, heart-shaped ribbed shell found in shallow bays and beaches. Edible locally and collected at low tide; easily recognized by rounded ribs and burrowing habit in tidal flats.
Fan mussel (pen shell)
Large, triangular pen shell anchored vertically in sediment, with shiny inner nacre. Once common, now critically endangered from disease and protected; notable for size and delicate fan-like appearance.
Freshwater pearl mussel
Long-lived river mussel that historically produced pearls. Indicator of pristine rivers and now threatened by pollution and habitat loss; heavy conservation focus on populations and host fish.
Asian clam
Small, round freshwater clam that reproduces rapidly and forms dense beds. Invasive in many regions, altering sediments and clogging infrastructure; identified by concentric growth rings on smooth shell.
Manila clam
Popular farmed clam with oval, patterned shell; cultured extensively for markets worldwide. Recognizable by fine radial and concentric patterns; a staple in seafood cuisine.
Atlantic surf clam
Large, heavy surf clam harvested commercially for canned and frozen products. Thick oval shell and strong siphons are identifiers; supports major fisheries along the Atlantic coast.
Horse mussel
Robust, elongated mussel forming dense reefs that provide habitat. Dark brown shell and byssal attachments distinguish it; ecologically important for benthic community structure.
Pismo clam
Plump, rounded surf clam living in sandy swash zones, popular for recreational diggers. Smooth, glossy shell and ability to burrow in wave-swept sand make it a recognizable beach species.
