Ray-finned fish belong to a very extensive class, which includes almost 95% of all the inhabitants of rivers, lakes, seas and oceans known to date. This class is widespread over all water bodies of the Earth and is a separate branch in the superclass of bone fish.
Radiant fishes (actinopterygii) got their name from Greek and Latin. It consists of two parts - “ray” and “feather”. This name has a connection with the structure of the fins.
Evolution
Since all species of marine fish and their freshwater counterparts are carefully studied, each archaeological find in this area is of interest to scientists. So it was found that the oldest skeleton of fossil ray-fin fish is older than 420 million years. According to its structure, it was determined that it was a predator belonging to the Paleoniscus order. Similar finds came across in Russia, Estonia and Sweden.
The following important finds were more than 200 million years younger. These were the skeletons of the first bony fish, which became the progenitors of a huge variety of species, subsequently named ray-finned fish. The emergence of a large number of species variations is explained by the fact that during evolution, fish were forced to adapt to different conditions and different levels of solar radiation. Related groups arose that were forced to adapt to the gradual changes in the world around them.
Primary classification
The entire class of "ray-finned fish" is divided into two separate groups:
Ganoid fish include 2 modern and 12 fossil orders. Newfishes belong to a younger group, the most numerous of which are bony fishes.
Despite the fact that they are representatives of the same class, they vary greatly in appearance and structure.
Radiant fishes. General characteristics of the group of ganoid fish
The first group, ganoid ray-finned fish, consists of only four orders. The most numerous and widespread of them are sturgeon-like. The structure of representatives of this detachment is rather primitive; their skeleton consists almost entirely of cartilage, in which there are no individual vertebrae. On the body there are 5 rows of bone diamond-shaped plates.
Cartilaginous ganoids differ from cartilaginous fish in the formed bones of the skull, gill covers and the presence of a swimming bladder. Sturgeon-shaped cartilaginous ganoids include some valuable commercial ray-fin fish, representatives of sterlet, sturgeon, beluga and others.
The structure of the group of bony fish
The second group is the most progressive. The body of bony fishes is covered with thin rounded bone plates, which are popularly called scales. The scales are located on the principle of tiles. On them, rings of growth are distinguishable, by which one can determine the age of an individual.
The backbone skeleton consists of individual ossified vertebrae, which are connected by ligaments, allowing the body of the fish to bend. Each segment of the spine, except for the cylindrical part, has an arc with a spinous process. The purpose of the upper arches of the vertebrae is to create a channel to protect the spinal cord. Down from the vertebrae, the transverse processes are directed to which the costal bones are attached.
Ray-finned fish from the bony group have a well-formed skull, consisting of a large number of bones. The brain is protected by a bone box. The skull is connected motionless to the bones of the spine.
The musculoskeletal system is formed by the skeleton and muscles that drive the fins, gill covers, and jaws. Radius fishes move due to the caudal region with a large fin. Stability and straightness during movement provide unpaired fins. And paired fins maintain the correct position of the body in the water and serve as rudders.
Variety of species
Freshwater ray-feathers and numerous species of marine fish, combined in one class, have different sizes and appearance. Moreover, the difference in size varies from 8 mm to 11 m. The weight of individual representatives can reach 2235 kg, we are talking about moon fish, which we managed to catch in 1908 in the Sydney area.
Radiation fish include all types of herring, numerous salmon-like fish, freshwater and sea eels, cyprinids, catfish, cod, stickleback, mullet and all types of perches and flounders.
Exotic species
You can make a huge list of interesting exotic inhabitants of the deep sea and home aquariums belonging to this class. The most striking of them are:
- Murjan fish, whose huge eyes contrast with the pinkish color of the scales;
- angel fish decorating the sea with bright stripes and nets of multi-colored scales;
- sea bass, the encounter with which can be dangerous, because it has a toxic substance in the fins;
- seahorse that can decorate any aquarium;
- Labotrophaeus fish bearing eggs in the mouth;
- a scalar that has earned fame among aquarists not only for its attractive appearance, but also for devotion to its pair.
A variety of representatives of this class appeared due to evolutionary processes. Today, most of the fish that live in the rivers, seas and oceans of our planet, or rather 95% of all existing species, belong to ray-creatures. Of course, to describe all the representatives is simply impossible. There are too many of them, but it is all the more interesting to study this class, finding more and more new information about it. It is not known whether all the inhabitants of the seas and oceans are familiar to mankind, perhaps new discoveries and sensations await us.