INTERNAL GILLS
· Pouched gills: in agnathans – lamp rays
· Septal gills: in chondrichthyes
· Aseptal gills: in osteichthyes
Pouched gills
· Large sac like branchial pouches which are lined with primary gill lamellae.
· Water goes through mouth àpharynx àpore shaped internal gill slitsàbranchial pouches.
· Water leaves the branchial pouches through pore shaped external gill slits.
Septal gills
· Branchial pouches are narrow chambers.
· Between the branchial chambers, para branchial chambers are present with external gill slits. External gill slits are small and slit shaped.
· Distal tips of the interbranchial septa can act as valves to close the external gill slits.
· Gill lamellae runs along the interbranchial septa towards the body surface.
· Internal gill slits rise from the pharynx and run into each branchial chamber.
Aseptal (non-septal) gills
· Operculum covers the gills.
· A single large opercula cavity is present with one valved external gill slit.
· Interbranchial septa are greatly reduced.
· Therefore gill lamellae extend freely into the opercula cavity.
(diagram: http://people.eku.edu)
