Name these organs which use a countercurrent system to extract large amounts of oxygen from water, found in fish.
These organs are protected by namesake "rakers" which prevent food from entering them. Unusual examples of these are found behind the legs of horseshoe crabs, and in some animals they are accessed through spiracles.  Asteroidea [aas-tur-oh-ee-DAY-uh]-class animals have simple versions of these called papulae [PAA-pyoo-lay] just under their skin. These organs are supported by a cartilaginous [kar-tih-LAA-jih-nuss] arch and protected by an operculum [oh-PUR-kyoo-lum], and their primary structures are lamellae [LAA- mih-lay], which have very large surface areas. Name these organs which use a countercurrent system to extract large amounts of oxygen from water, found in fish.
These organs are protected by namesake "rakers" which prevent food from entering them.
gills