Ray-finned fish belong to a very large class, which includes almost 95% of all currently known inhabitants of rivers, lakes, seas and oceans. This class is distributed throughout all water bodies of the Earth and is a separate branch in the superclass of bony fish.
Ray-finned fish (actinopterygii) get their name from Greek and Latin. It consists of two parts - "beam" and "feather". This name has a connection with the structure of the fins.
Evolution
Because all types 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-finned fish is older than 420 million years. According to its structure, it was determined that it was a predator belonging to the order of paleonisciformes. Similar finds came across on the territory of Russia, Estonia and Sweden.
The following important finds turned out to be younger than 200 million years. These were the skeletons of the first bony fish, which became the progenitors of a huge variety of species, later called ray-finned fish.fish. The emergence of a large number of species variations is explained by the fact that in the course of evolution, fish were forced to adapt to different conditions and different levels of solar radiation. Kindred groups emerged and were forced to adapt to the gradual changes in the world around them.
Primary classification
The whole class "ray-finned fish" is divided into two separate groups:
- ganoid fish;
- new-finned fish.
Ganoid fish include 2 modern and 12 fossil orders. New-finned fish belong to a younger group, the most numerous species of which are bony fish.
Despite the fact that these are representatives of the same class, they differ greatly in appearance and structure.
Ray-finned fish. General characteristics of the group of ganoid fish
The first group, the ganoid ray-finned fish, consists of only four orders. The most numerous and widespread of them are sturgeons. The structure of the representatives of this detachment is quite primitive, their skeleton almost entirely consists of cartilage, in which there are no individual vertebrae. On the body are arranged in 5 rows of bony rhomboid plates.
Cartilaginous ganoids differ from cartilaginous fishes in the formed bones of the skull, gill covers and the presence of a swim bladder. Sturgeon-like cartilaginous ganoids include some valuable commercial ray-finned fish, representatives - sterlet, sturgeon, beluga and others.
Structure of the bony groupfish
The second group is the most progressive. The body of bony fish is covered with thin rounded bony plates, which are popularly called scales. Scales are located according to the principle of tiles. Growth rings are distinguishable on them, by which one can determine the age of an individual.
The skeletal skeleton consists of separate ossified vertebrae, which are connected by ligaments that allow 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 canal to protect the spinal cord. Down from the vertebrae are the transverse processes, 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 fixedly connected to the bones of the spine.
The musculoskeletal system is formed by the skeleton and muscles that move the fins, gill covers, jaws. Ray-finned fish move thanks to the tail section with a large fin. Stability and straightness during movement are provided by unpaired fins. And paired fins maintain the correct position of the body in the water and serve as rudders.
Diversity of species
Freshwater ray-finned and numerous species of marine fish, united in one class, have different sizes and appearances. At the same time, the difference in size ranges from 8 mm to 11 m. The weight of individual representatives can reach 2235 kg, we are talking about the moon fish,who managed to catch in 1908 in the Sydney area.
Ray-finned fish include all types of herring, numerous salmon-like fish, freshwater and s altwater 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 aquaria belonging to this class. The brightest of them are:
- Murjan fish, whose huge eyes contrast with the pinkish color of the scales;
- angel fish that decorates the sea with bright stripes and nets of colorful scales;
- sea bass, which can be dangerous to meet because it has a poisonous substance in its fins;
- seahorse that can decorate any aquarium;
- labeotropheus fish that hatches eggs in its mouth;
- angelfish, which has gained fame among aquarists not only for its cute appearance, but also for its devotion to its mate.
The variety of representatives of this class appeared as a result of evolutionary processes. To date, most of the fish that live in the rivers, seas and oceans of our planet, or rather 95% of all existing species, are ray-finned. Of course, it is simply impossible to describe all the representatives. 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 for certain whether all the inhabitants of the seas and oceans are familiar to mankind, perhaps new discoveries and sensations await us.
