noun
gill slit
The external opening of a fish's gill chamber; a standard anatomical term.
サメの鰓孔は体の側面に並んでいる。
The shark's gill slits are lined up on the side of its body.
noun
pharyngeal slit
In vertebrate embryology, a structure homologous to gill slits; more technical than sense 1.
発生学では、鰓孔は咽頭裂とも呼ばれる。
In embryology, the pharyngeal slit is also called a pharyngeal cleft.
Compound of 鰓 (えら, 'gill') and 孔 (あな, 'hole'). The reading さいこう is the on'yomi reading of the kanji, used in technical contexts.