Mary Allen
Introduction to Gills
Gills are respiratory organs found in many aquatic animals that allow them to extract oxygen from water. They are typically located on the sides of the animal’s body and consist of thin, flat structures that are highly vascularized. As water flows over the gills, oxygen is diffused into the bloodstream while carbon dioxide and other waste gases are removed. Gills come in many different shapes and sizes, and are found in a wide variety of aquatic animals.
Fishes: The Most Common Gilled Animals
Fishes are the most common type of animal with gills. They have a wide variety of gill structures, depending on their species and habitat. Some fishes, such as sharks and rays, have five to seven pairs of gill slits that run along the sides of their head. Other fishes, such as salmon and trout, have gill arches that are covered by a bony plate called an operculum. The majority of fishes are able to extract enough oxygen from water to support their metabolism and activity levels, but some species, such as lungfishes, can also breathe air.
Cartilaginous Fishes: Sharks, Rays, and Chimaeras
Cartilaginous fishes, which include sharks, rays, and chimaeras, have a unique gill structure that differs from other fishes. Their gill slits are not covered by an operculum and are instead exposed to the water. Sharks are able to actively pump water over their gills, while rays and chimaeras rely on the movement of water over their gills as they swim. These animals have a highly efficient respiratory system that allows them to extract enough oxygen from water to support their high metabolic rates.
Bony Fishes: The Largest and Most Diverse Group
Bony fishes, which include the majority of the fish species, have a wide variety of gill structures. Some, such as perch and tuna, have gill arches covered by an operculum, while others, such as eels, have gill slits that are partially covered by skin. Bony fishes have a highly efficient respiratory system that allows them to extract enough oxygen from water to support their activity levels. They are able to adjust the size of their gill openings to regulate the amount of water flowing over their gills, which helps them to conserve energy.
Amphibians: Gilled Larvae, Lung-Breathing Adults
Amphibians, which include frogs, toads, and salamanders, are unique in that they have gills as larvae but breathe air as adults. The gills of amphibian larvae are located on the outside of their body and are similar in structure to those of fishes. As they develop into adults, many amphibians lose their gills and develop lungs. However, some species, such as the axolotl, retain their gills throughout their life.
Crustaceans: The Gills in Their Exoskeletons
Crustaceans, which include crabs, lobsters, and shrimp, have gills located in their exoskeletons. These animals are able to extract oxygen from water by pumping it over their gills using specialized appendages. Some crustaceans, such as crabs, also have gills located inside their carapace, which helps to increase their respiratory efficiency.
Mollusks: The Gills in Snails, Clams, and Squids
Mollusks, which include snails, clams, and squids, have gills located inside their mantle cavity. These animals are able to extract oxygen from water by pumping it over their gills using specialized cilia. Mollusks have a highly efficient respiratory system that allows them to extract enough oxygen from water to support their activity levels.
Echinoderms: The Gills in Sea Urchins and Starfishes
Echinoderms, which include sea urchins and starfishes, have a unique type of gill called a water vascular system. This system pumps seawater through a series of channels and into specialized structures called tube feet, which are used for respiration and locomotion. Echinoderms have a highly efficient respiratory system that allows them to extract enough oxygen from water to support their activity levels.
Aquatic Insects: The Gills in Mosquitoes and Stoneflies
Aquatic insects, which include mosquitoes and stoneflies, have a variety of gill structures that allow them to extract oxygen from water. Some insects, such as mosquito larvae, have specialized structures called siphons that allow them to extract oxygen from the surface of the water. Other insects, such as stoneflies, have gill structures located on the outside of their body.
Tadpoles: The Gills in Frog and Toad Larvae
Tadpoles, the larvae of frogs and toads, have gills located on the outside of their body. These gills are similar in structure to those of fish and allow the tadpole to extract oxygen from water. As they develop into adults, frogs and toads lose their gills and develop lungs.
Lampreys: Jawless Fishes with Gills and No Jaws
Lampreys are a type of jawless fish that have a unique gill structure. They have seven pairs of gill openings that are not covered by an operculum. Lampreys are able to extract enough oxygen from water to support their metabolism and activity levels, but they are also able to breathe air through their skin.
Hagfishes: The Slimy Fishes with Gills and No Jaws
Hagfishes are a type of jawless fish that have a unique gill structure. They have five to sixteen pairs of gill openings that are not covered by an operculum. Hagfishes are able to extract enough oxygen from water to support their metabolism and activity levels, but they are also able to breathe air through their skin. Hagfishes are also known for their slimy secretions, which they use for defense and to help them move through narrow spaces.