Variety of Fascinating Fishes in the underwater world-நீருக்கடியில் உலகி...
Fish are gill-bearing aquatic craniate animals that lack limbs with digits. They form a sister group to the tunicates, together forming the olfactores. Included in this definition are the living hagfish, lampreys, and cartilaginous and bony fish as well as various extinct related groups. Around 99% of living fish species are ray-finned fish, belonging to the class Actinopterygii, with over 95% belonging to the teleost subgrouping. Many fish of the Paleozoic developed external armor that protected them from predators. The first fish with jaws appeared in the Silurian period, after which many (such as sharks) became formidable marine predators rather than just the prey of arthropods. Fish are abundant in most bodies of water. . With 34,300 described species, fish exhibit greater species diversity than any other group of vertebrates. Most fish are ectothermic ("cold-blooded"), allowing their body temperatures to vary as ambient temperatures change, though some of the large activ