Pouched gills . Charactgeristic of Agnatha. Gill filaments in pouchlike chambers. Septal gills . Gill chambers larger, communicate more widely with pharynx.
Gill slits present.
Elasmobranchs Spiracle Hemibranch anteriorly. Opercular gills . Characteristic of Osteichthyes. Most bony fishes lose spiracle, but some may retain pseudobranch. Functional gills of bony fishes usually consist of 4 holobranchs.