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Amphibians have soft bodies with thin skins, and lack claws, defensive armour, or spines. Nevertheless, they have evolved various defence mechanisms to keep themselves alive. The first line of defence in salamanders and frogs is the mucous secretion that they produce. This keeps their skin moist and makes them slippery and difficult to grip.
Amphibians are ectothermic, anamniotic, four-limbed vertebrate animals that constitute the class Amphibia.In its broadest sense, it is a paraphyletic group encompassing all tetrapods excluding the amniotes (tetrapods with an amniotic membrane, such as modern reptiles, birds and mammals).
All living amphibians belong to the group Lissamphibia. They inhabit a wide variety of habitats, with most species living within terrestrial, fossorial, arboreal or freshwater aquatic ecosystems. Thus amphibians typically start out as larvae living in water, but some species have developed behavioural adaptations to bypass this.
Amphibious fish are fish that are able to leave water for extended periods of time. About 11 distantly related genera of fish are considered amphibious. This suggests that many fish genera independently evolved amphibious traits, a process known as convergent evolution .
Coelacanth eggs are large, with only a thin layer of membrane to protect them. Embryos hatch within the female and eventually are born alive, which is a rarity in fish. This was only discovered when the American Museum of Natural History dissected its first coelacanth specimen in 1975 and found it pregnant with five embryos. [67]
The hippopotamus (Hippopotamus amphibius) (/ ˌ h ɪ p ə ˈ p ɒ t ə m ə s /; pl.: hippopotamuses; often shortened to hippo (pl.: hippos), further qualified as the common hippopotamus, Nile hippopotamus, or river hippopotamus, is a large semiaquatic mammal native to sub-Saharan Africa.
It has been estimated there are as many as 7.77 million animal species on Earth. Animal body lengths range from 8.5 μm (0.00033 in) to 33.6 m (110 ft). They have complex ecologies and interactions with each other and their environments, forming intricate food webs.