出典:Wiktionary
出典:Wikipedia
出典:『Wikipedia』 (2011/05/09 18:08 UTC 版)
Gill slits are individual openings to gills, i.e., multiple gill arches, which lack a single outer cover. Such gills are characteristic of Cartilaginous fish such as sharks, rays, sawfish, and guitarfish. Most of these have five pairs, but a few species have 6 or 7 pairs. The anterior edge of a gill slit is motile, moving outward to allow water to exit, but closing to prevent reverse flow. In contrast, Bony fishes have a single outer bony gill covering called an operculum.