Skip to content

Bivalvia sp.

Bivalves are the class of molluscs whose shell is made of two valves joined by a hinge: clams, oysters, mussels and scallops. 1 2 3 There are about 9,200 species, in the sea and in fresh water, and almost all feed by filtering the water. 2 3

Bivalvia sp.

At a glance

Data from the scientific sources listed at the bottom.

Conservation

NEDDLCNTVUENCREWEX

IUCN Red List: not evaluated. The Red List assesses individual species, not the class. For example, the giant clam, Tridacna gigas, is classified as Critically Endangered (assessment of 23 May 2024) and is in CITES Appendix II. 4

Where it lives

They live in almost the whole ocean, from the tropics to the Arctic and from the coasts to the abyss; some species live by hydrothermal vents in the Pacific, at more than 13,000 feet (about 4,000 m). 2 Many species live in fresh water. 3

How to recognise it

Tap a number on the photo: the key explains what to look for.

123
  1. 1Two valves the shell is in two parts joined by a hinge 2
  2. 2Gap between the valves the water to be filtered comes in through an opening or siphons 3
  3. 3On a hard substrate many species attach to rock with their byssus 3

Life in the wild

Where it is found

Some bivalves live buried in the seabed, others attach to hard surfaces or to each other with byssal threads or an adhesive. 3 As adults most move little; the young are more mobile and serve to spread the species. 3 Oyster reefs and freshwater mussel beds are centres of biodiversity. 3

What it eats

Almost all filter suspended particles from the water with their gills, which they also use to breathe. 2 3 Some species, especially among the burrowing ones, eat detritus from the bottom. 3 Giant clams and some small Indo-Pacific bivalves host symbiotic algae in their mantle that supply part of their food; some species from extreme environments, such as hydrothermal vents, host bacteria that produce nutrients from sulphur. 3

Behaviour

Some species extend a pointed, retractable foot to dig or move through the sediment. 2 The mantle produces the calcium carbonate that makes the shell grow. 2

Reproduction

Life strategies are very varied. 3 Many marine species have larvae that live in the plankton, where they are eaten by comb jellies and jellyfish and can be filtered out by adult bivalves themselves; some species have parasitic larvae. 3

In the aquarium

From the experience of the BallingMania community.

Community rating

No rating in the original sheet.

Original sheet

Bivalves (Bivalvia Linnaeus, 1758), also called lamellibranchs or pelecypods, are a class of the phylum Mollusca, comprising 13,000 species, generally marine, although there are also freshwater ones. They have a laterally compressed body enclosed in a shell made of two hinged parts. Bivalves include clams, oysters, tellins, mussels, scallops and numerous other species that live in salt water. Most are filter feeders, that is, they filter the water, retaining food particles and phytoplankton in suspension. Their gills have evolved into organs specialised for feeding and breathing. Most bivalves bury themselves in sediment or sand, where they are relatively safe from predators, while others attach themselves to rocks or other hard surfaces.

good or bad?

VERDICT:

Key: Good! An organism beneficial to the system. Reef Safe!

An organism whose benign or harmful nature is not yet known, to be kept an eye on.

Bad! The organism is a threat to the other inhabitants of the aquarium or could become a pest.

A food source for the other inhabitants of the aquarium.

A potentially toxic or venomous organism.

© Oysterk · © GAV

Did you know?

The oysters and mussels of the Marennes-Oléron bay, in France, can filter all the water in the bay in about 2.7 days. 3
The giant clam reaches 137 cm in length and 500 kg in weight. 4

Sources

  1. WoRMS Editorial Board (2026). Bivalvia Linnaeus, 1758. World Register of Marine Species.
  2. NOAA National Ocean Service (2026). What is a bivalve mollusk?. National Oceanic and Atmospheric Administration.
  3. Vaughn C.C., Hoellein T.J. (2018). Bivalve impacts in freshwater and marine ecosystems. Annual Review of Ecology, Evolution, and Systematics 49: 183-208.
  4. (2026). Tridacna gigas (Linnaeus, 1758). SeaLifeBase.

Sources checked on 5 November 2026. Community texts and ratings are kept separate from the scientific data.

Download the original sheet (Italian)All species