Temporal range: Cambrian – Recent
Mussels in the intertidal zone in Cornwall, England
Scientific classification
Linnaeus, 1758
A large number of venerid bivalves with their siphons visible
Shell of the giant clam (Tridacna gigas)
Empty shell of the giant clam
(Tridacna gigas)
The world's largest clam (187 cms), a Sphenoceramus steenstrupi fossil from Greenland in the Geological Museum in Copenhagen

The bivalves are a large class of molluscs, also known as pelecypods.

They have a hard calcareous shell made of two parts or 'valves'. The soft parts are inside the shell. The shell is usually bilaterally symmetrical.

There are over 30,000 species of bivalves, including the fossil species. There are about 9,200 living species in 1,260 genera and 106 families. All of them live in the water, most of them in the sea or in brackish water. Some live in fresh water. All are filter feeders: they lost their radula in the course of evolution. A few are carnivorous, eating much larger prey than the tiny microalgae eaten by other bivalves.

The best known examples of bivalves are clams, mussels, scallops and oysters.[1]


Bivalves have two shells or valves connected by a hinge with hinge teeth. They are made of a calcareous mineral, calcite or aragonite. The valves are covered by a periostracum, which is an organic horny substance. This forms the familiar coloured layer on the shell.

The shells are usually held shut by strong adductor muscles. Scallops can use their muscles to flap the valves and swim.[2]

Other Languages
Afrikaans: Tweekleppige
asturianu: Bivalvia
Avañe'ẽ: Mymba ijyta mokõi
azərbaycanca: İkitaylılar
Bân-lâm-gú: Siang-khak-kong
беларуская: Двухстворкавыя
беларуская (тарашкевіца)‎: Двухстворкавыя
български: Миди
brezhoneg: Daougleureged
català: Bivalves
Cebuano: Ukab-ukab
čeština: Mlži
dansk: Muslinger
Deutsch: Muscheln
eesti: Karbid
Ελληνικά: Δίθυρα
English: Bivalvia
español: Bivalvia
Esperanto: Duvalvulo
euskara: Bivalvia
français: Bivalvia
Gaeilge: Débhlaoscach
galego: Bivalvos
한국어: 이매패류
हिन्दी: पटलक्लोमी
hrvatski: Školjkaši
Ido: Bivalvo
Bahasa Indonesia: Bivalvia
interlingua: Bivalvia
íslenska: Samlokur
italiano: Bivalvia
עברית: צדפות
Basa Jawa: Bivalvia
Latina: Bivalvia
latviešu: Gliemenes
Lëtzebuergesch: Muschelen
lietuvių: Dvigeldžiai
Lingua Franca Nova: Bivalva
magyar: Kagylók
македонски: Школки
Bahasa Melayu: Bivalvia
Nederlands: Tweekleppigen
日本語: 二枚貝
Nordfriisk: Twiiskaalagen
norsk: Muslinger
norsk nynorsk: Muslingar
oʻzbekcha/ўзбекча: Ikki pallalilar
ਪੰਜਾਬੀ: ਸਿੱਪੀਆਂ
پنجابی: سپیاں
Plattdüütsch: Musseln
polski: Małże
português: Bivalvia
română: Bivalve
Runa Simi: Lakachu
Scots: Bivalvia
slovenčina: Lastúrniky
slovenščina: Školjke
српски / srpski: Шкољке
srpskohrvatski / српскохрватски: Školjke
suomi: Simpukat
svenska: Musslor
Tagalog: Bivalvia
తెలుగు: ఆల్చిప్ప
Türkçe: Bivalvia
українська: Двостулкові
West-Vlams: Twêekleppign
Winaray: Bivalvia
粵語: 雙殼綱
中文: 双壳纲