gill slit in fish and other aquatic animals

The gill-bearing arch or its vestigial crease found on the sides of the neck of vertebrates.

lamprey; a jawless fish of the family Petromyzontidae; also known as a lampern

to fail an imperial examination or suffer a major career setback; literally to expose one's gills at the Dragon Gate

a reddish invertebrate that lives on the deep sea floor and can emit light

Lamellibranchia; a class of mollusks commonly known as bivalves

the protective bony flap covering the gills of a fish; characteristic of bony fish

(literary) to be cautious or fearful