Cartilaginous fish were, of course, before their bony counterparts.But whether this fact makes it possible to assert that these ancient creatures - imperfect children of nature, play compared to their more advanced "colleagues"?Consider the basic differences.The main feature, which is why the class got its name, is a cartilaginous skeleton.Also, they do not swim bladder (although it is not certain and bony fish, e.g., flounder y).Since the specific weight of the animal is heavier than water, it is not to go down, it must always be in motion.Placed in an aquarium, they just suffocate even if the water is clear: in order to saturate the blood with oxygen, it is necessary to pump a lot of water through the gills, which is achieved by continuous motion.
Next cartilaginous fish have gill covers as bone.Slots overt airway.They are located on the side of the head.In holocephali (chimeras) only one gill slit, sharks and rays have several.In addition, the back of the animal's eyes is another Gill - Spiracle.Sharks is a rudiment, and stingrays actively use Spiracle (it is located on top of their heads) when waiting for their prey buried in the sand.When swimming, these creatures swallow mouth water and release it through the hole.
What else distinguishes the class "cartilaginous fish"?General description of them is that they all have placoid scales.These are special plates, tooth capped with one or two edges.Of those spikes consist rays, fin spines of some species of sharks' teeth, saw "a fish-saw, and, by the way, true, being in the jaw, teeth, cartilage class.But here there is a similarity with chimeras dvoyakodyshaschmi - chewing their bodies merged into two plates, the grinding plant foods.Also note that the chimera has the traits of a population of bony depths - chord they retain throughout their lives.The name itself (as the ancient Greeks dubbed mythical creatures, combines the features of various creatures - the centaur, sphinx) characterizes these strange creatures: they not only merged anatomical features of bone and cartilage, but their tail resembles a rat's why they are also called "searats ".
Class "cartilaginous fish" is divided into two subclasses: holocephali (Chimera) and elasmobranch.This is divided into two groups: the sharks and stingrays.Their representatives have a lot of similarities between them.We can say that stingrays - is "flattened sharks," though such a statement is too simplistic.Gill slits they are in the belly, while toothed hischnits- sides.There are about 350 species of skates and rays: among them there pilorylye (not to be confused with pilonosymi sharks!), Stingray and high.If the stingray strike their prey with poison that is injected into the body through the spike, then kill her electric high-voltage discharge.The greatest view of the world - Manta - with their giant size (scale of the "wings" up to 8 meters) feeds on plankton.
But the most popular in human culture are cartilaginous fishes such as sharks.They are about 250 species, and they are distributed in all oceans, from the equator to the polar latitudes.Their sizes range from 15 centimeters (cat) of up to 20 meters (whale).Not only the temperature of the water does not scare the sharks, but its salinity: they met in the mouths and downstream, where they were sailing in the hope to attack the migrating herds of deer.In literature and film, they deserve not very flattering title always hungry stomach without brains, greedy and insatiable.The concept of "fetal kainizm" came into use after people found that live-bearing fish eat each other embryos in the womb.
Are cartilaginous fish dozhivshim to our time a class of prehistoric animals, a kind of stalemate in the development, as some ichthyologists?Yes, they have not held the formation of skeleton, but that does not mean that their soft bones.Under the influence of the backbone of the mineralization is not inferior to other types of hardness.Some characteristics (no gill slits and swim bladder) they show the evolutionary "slack" in comparison with kostevymi but have internal fertilization, and many of their species - viviparous or ovoviviparous.And some even sharks produced "baby seat" as in placental animals.
