二枚貝(にまいがい)

Composed of 二枚(にまい) ('two sheets / two flat objects,' using the counter 枚(まい) for thin, flat things) + 貝(かい) (shellfish). The two halves of a bivalve's shell are counted as flat 'sheets,' giving the word its literal meaning 'two-sheet shellfish.' When 貝(かい) appears as the second element of a compound, it is read がい (rendaku).

Common collocations

• 二枚貝(にまいがい)類(るい): bivalves (as a biological group)
• 二枚貝(にまいがい)の仲間(なかま): members of the bivalve family
• 二枚貝(にまいがい)の砂抜(すなぬ)き: removing sand from bivalves (before cooking)
• 二枚貝(にまいがい)の養殖(ようしょく): bivalve farming / aquaculture
• 二枚貝(にまいがい)の殻(から): a bivalve shell

COMMON 二枚貝(にまいがい):

• アサリ (浅蜊(あさり)): Manila clam — small, most common in miso soup and pasta.
• シジミ (蜆(しじみ)): freshwater basket clam — very small, used in miso soup.
• ハマグリ (蛤(はまぐり)): hard clam — larger, traditional in ひな祭(まつ)り soup.
• ホタテ(ガイ) (帆立貝(ほたてがい)): scallop — prized for its large adductor muscle.
• カキ (牡蠣(かき)): oyster — eaten raw or cooked; a major aquaculture product.
• ムール貝(がい): mussel — loanword + 貝(がい).

Similar words

• 巻(ま)き貝(がい): univalve, snail, gastropod — shellfish with a single spiral shell; the main biological counterpart of 二枚貝(にまいがい).
• 貝(かい) / 貝類(かいるい): shellfish (in general) — the broader cover term including both bivalves and univalves.
• 甲殻類(こうかくるい): crustaceans — a separate group including shrimp, crabs, and lobsters; not shellfish in the biological sense, but often grouped with them culinarily.

Biology note

Bivalves are filter feeders that pump water through gills to extract plankton and organic particles, which makes them sensitive indicators of water pollution. They can also accumulate toxins from harmful algal blooms, which is why shellfish advisories warn specifically about 二枚貝(にまいがい).