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Secondary aquatic adaptations tend to develop in early speciation as the animal ventures into water in order to find available food. As successive generations spend more time in the water, natural selection causes the acquisition of more adaptations. Animals of later generations may spend most their life in the water, coming ashore for mating.
Aquatic animals generally conduct gas exchange in water by extracting dissolved oxygen via specialised respiratory organs called gills, through the skin or across enteral mucosae, although some are evolved from terrestrial ancestors that re-adapted to aquatic environments (e.g. marine reptiles and marine mammals), in which case they actually ...
Adult salamanders often have an aquatic phase in spring and summer, and a land phase in winter. For adaptation to a water phase, prolactin is the required hormone, and for adaptation to the land phase, thyroxine. External gills do not return in subsequent aquatic phases because these are completely absorbed upon leaving the water for the first ...
Sleeping the season away. If an animal’s physiology, diet, or other characteristics don’t allow it to stay warm and/or find sufficient food during the winter, an additional set of survival ...
Wading and bottom-feeding animals (such as manatees) need to be heavier than water in order to keep contact with the floor or to stay submerged. Surface-living animals (such as sea otters) need the opposite, and free-swimming animals living in open waters (such as dolphins) need to be neutrally buoyant in order to be able to swim up and down ...
It seems to have been adapted to water much like a beaver, with teeth different in many ways from all other docodonts, presumably due to a difference in diet. Most docodonts had teeth specialized for an omnivorous diet. The teeth of Castorocauda suggest that the animal was a piscivore, feeding on fish and small invertebrates.
Mangrove killifish (Mangrove rivulus): It can survive for about two months on land, where it breathes through its skin. Eels: Some eels, such as the European eel and the American eel, can live for an extended time out of water and can also crawl on land if the soil is moist. The moray Echidna catenata sometimes leaves the water to forage. [7]
Euryhaline organisms are able to adapt to a wide range of salinities. An example of a euryhaline fish is the short-finned molly, Poecilia sphenops, which can live in fresh water, brackish water, or salt water. The green crab (Carcinus maenas) is an example of a