What is Actinopterygii and Elasmobranch?

kelolalaut.com - Actinopterygii is a class of bony fish, they comprise over 50% of living vertebrate. This fish is so called because of their fins that look like webs of skin supported by bony structure. Actinopterygii dominates the species of fish with nearly 99% over 30.000 fish species. You can find them in freshwater or marine environment, from the highest mountain stream to the deepest ocean. This type of fish certainly have so much range in size. The smallest like Paedocypris is just 8 mm, while the largest is ocean sunfish that can weigh up to 2,300 kg. Actinopterygians may have different scales type depend on their species. 

There are five major development of Actinopterygii in general: embryonic, larvae, juvenile, adult and senescent. In most of bony fish sex are separated and fertilization happened externally. However in some species can be found cases like sequential hermaphrodite. This mean that the individual can change its sex at some point in its life. Most cases the fish starting life as a female then become a male at some stage. This changes can be triggered by internal or external factors.

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Elasmobranch is refer to cartilaginous fish like sharks, rays and skate. Cartilage is type of bones that made our ears and nose. This type of bones is flexible and durable and weigh just half as much as true bones. The elasmobranch skeleton is made of cartilage and connective tissue. Elasmobranch breathe with their five to seven pair of gills. While many fish maintain their buoyancy with their swim bladder, a gas-filled organ in their body, Cartilaginous fish maintain their buoyancy with large liver full of oil. 

The different between sharks and rays or skate is the way they swims. Sharks move by swinging their tail side to side, while rays and skate swim by flapping their large pectoral fin. Cartilaginous fish covered in though skin and have placoid scale types. This types of scales make their skin feel like sand paper when it touched in opposite direction. Cartilaginous fish is provide by two function of this type of scales, protection and streamlining. Cartilaginous fish also have several sensory organs that helps them process the information of their surrounding. This sensory organ is called electroreceptor that helps them sense electric field in the water. Electroreceptor is used to find their prey, sense water temperature, and can be used as navigation system. Most development of their embryos are ovoviviparous (live birth after the eggs hatch in the mother’s oviduct), some are oviparous (laying fertilize eggs in the waters), and in rare case there is viviparous (live birth of their young) species.

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