A gill that develops in the walls of the pharynx along a series of gill slits opening to the exterior. In fish, the gills are located on both sides of the pharynx. [ http://en.wikipedia.org/wiki/Gill#Vertebrate_gills ]
- A gill that develops in the walls of the pharynx along a series of gill slits opening to the exterior. In fish, the gills are located on both sides of the pharynx.
- Gills are made of filaments which help increase surface area for oxygen exchange
- In bony fish, the gills are covered by a bony cover called an operculum. When a fish breathes, it opens its mouth at regular times and draws in a mouthful of water. It then draws the sides of its throat together, forcing the water through the gill openings. The water passes over the gills on the outside. Valves inside the mouth keep the water from escaping through the mouth again. The operculum can be very important in adjusting the pressure of water inside of the pharynx to allow proper ventilation of the gills. Lampreys and sharks lack an operculum, they have multiple gill openings. Also, they must use different methods to force water over the gills. In sharks and rays, this ventilation of the gills is achieved either by the use of spiracles or ram ventilation (ventilation by constantly swimming). Although some animals use this method it is much better for animals to use a spiracle because they are less susceptible to injury