Fish are a separate group of vertebrates. Given vertebrates, are there fish without bones?
Pisces - General Description
Fishes are maxillofacial animals, but jawless are considered their ancient ancestors, the fossilized remains of which are over 500 million years old. Fish can live in both salt and fresh water. They are of great value in various fields. In particular, they play an important role in aquatic ecosystems and are also of commercial importance.
According to 2019 data, more than 35,000 species have been found. Of these, approximately 3,000 live in the waters of Russia. But these indicators are not the limit. Up to 500 descriptions of new species appear annually. Their diversity is quite large - there are individuals ranging in size from 7.9 mm to 20 m.
The body of most fish is covered with scales. Its structure depends on a particular class. The skin can acquire any shades - neutral, bright, camouflage. Fish move in the aquatic environment and perform other actions due to the musculoskeletal system, represented by a system of organs and tissues. The main “engine" is paired and unpaired fins.
Fish have good vision (with the exception of some blinded deep-sea or cave species). They also have a developed sense of smell, taste. Many receptors allow these animals to determine the chemical composition of water. The lateral line and the inner ear allow you to navigate perfectly in space.
Interesting fact: Fishes are considered to be silent creatures because they do not have a vocal apparatus. However, in fact, they communicate with each other through various sounds. Various parts of the body are used to reproduce them: teeth, bones, vibrating muscles near the swimming bladder.
The respiratory function is carried out using gills, which can be closed by gill covers in some species. In terms of nutrition, fish are divided into predators, herbivores, detritophages (feed on organic debris) and omnivores. Some absorb plankton. Also, fish can change their diet depending on age.
Pisces is characterized by self-regulation in the form of osmotic pressure. They reproduce in several ways, depending on the species - by live birth, egg production and egg production.
What are the classes of fish?
There are two main classes of fish:
- bone
- cartilaginous.
There are also additional classes, such as ray-fin and lap-fin, which are related to bone fish. 2 classes are considered extinct: acanthodes and placoderma.
The main difference between bone and cartilaginous fish is hidden in the class names. So, bone fish have a full bone skeleton. In the class of cartilaginous fish, the skeleton is represented by cartilage, which have sufficient strength and elasticity due to minerals.
Thus, fish without bones are representatives of the cartilage class. There are also some families of bone fish in which the number of bones is significantly less than that of other relatives. These include sturgeon.The total number of varieties of cartilage species is about 1000.
The characteristic features of cartilaginous fish that distinguish them from bone:
- cartilage skeleton;
- no gill covers;
- no swim bladder;
- placoid scales (in bone - ganoid, ctenoid or cycloid with an additional layer of mucus);
- horizontal fins.
Interesting fact: Bone fish have a swim bladder that supports buoyancy. They need to spend a minimum of energy to stay at the right depth or freeze in one position. Cartilaginous swim bladders do not, therefore, these fish are forced to constantly move.
The class of cartilaginous fish is also represented by two subclasses: plate-branchial and whole-headed. Representatives of the first subclass are sharks and stingrays. The modern whole-headed population is represented only by chimeras, the rest are considered extinct.
Lack of bones is characterized by one of the classes of fish, namely, cartilaginous. This class is represented by sharks, stingrays, chimeric fish. Instead of the bone skeleton, their musculoskeletal function is supported by the cartilage skeleton. Thanks to numerous minerals, cartilage is endowed with sufficient strength. Some bone fish (sturgeon) have fewer bones than other families. In particular, their muscles do not contain small bones.
