The oldest now living on the earth spider - a scorpion.Gone for millions of years, and they have not changed.Today, science knows more than 700 of their species.
Scorpions - not only the inhabitants of the desert, as is commonly believed.They also are found in the humid and hot tropical and subtropical regions, some species can be found in cooler places - in the mountains at high altitudes.But ticks - a relatively young group of arachnid arthropods.But in his article, I will prefer not to mites, and scorpions, namely, spiders, even though I'm not particularly their liking.It is interesting to see how the process of evolution going on a reduction and simplification of the external structure of the spider caused by merging segments and distinguishes it from a scorpion.Here, I'll answer the age-old dispute over how many legs a spider, as well as tell you, from what turns his web.Let's go!
As he looks
external structure of spider also distinguishes it from insects.If their body is clearly composed of three sections: the head, thoracic and abdominal, then the spider of only two departments: cephalothorax, formed by the merger of the head and chest and composed of chitin, durable, and soft abdomen.On the cephalothorax located eight eyes already!Do not be surprised, but generally the minimum number of spider eyes - six, the maximum - twelve.Cephalothorax connected to the soft abdomen is very thin and a small tube.At the end of unsegmented abdomen positioned so called spinneret.Their destiny I'll tell you later.
How many legs a spider
Many of us still can not correctly answer the question about how many legs a spider and probably think that their six, like all insects.But there it was!Herein lies the major difference - the presence of exactly eight feet, whereas insects, indeed, all three pairs of legs.The first pair of spider legs - chelicerae.This poisonous head limb serving for gripping and grinding food.Further there are three pairs of legs designed for walking.Here we are with you and know how many legs a spider, from which departments he is as a pair of eyes, and perhaps most importantly - he is not an insect!This is its main external signs.Go to an internal "review of the Spider."
internal structure of spider
This nervous system is controlled by the brain, located in the cephalothorax.There is a spider and the heart, which is located in the upper front part of the soft abdomen (red in the figure).Heart rate is 30-70 strokes per minute, but if the spider for any reason strained or exhausted, then the frequency is increased to 200 ... bpm!At the end of the abdomen are located so-called spinning bodies.They produce silk glands and associated with producing various proteins.As a result of the mixing and polymerization of proteins obtained watery silk flowing through special bodies spinning and turning into a thread.Here it is - the web! Habitat
Spiders spread completely around the world - from Antarctica and mountainous areas to the deep gorges and caves.Many of them live on land, and some - in the sea, in freshwater springs and groundwater.
