How many legs does a spider, or Why is it not akin to an insect?
The most ancient of the arachnids living on Earth are scorpions. Millions of years have passed, and they have not changed much. To date, science knows more than 700 of their species.
Scorpions are not only desert inhabitantslocalities, as it is commonly believed. They are found also in humid and hot tropics and subtropics, some species can be found in cooler places - in the mountains at high altitudes above sea level. But ticks are a relatively young group of arachnid arthropods.But in my article I will give preference not to ticksand scorpions, namely spiders, although I do not particularly like them. It is interesting to see how in the process of evolution, the spider's external structure decreased and simplified, caused by the merging of segments and distinguishing it from the scorpion. Here I will answer the age-old controversial question about how many legs a spider has, and also tell you what its cobwebs are from. Go!
What does he look like
The external structure of the spider is also fundamentallydistinguishes it from insects. If their body clearly consists of three divisions: head, thoracic and abdominal, the arachnids of these divisions have only two: the cephalothorax, formed by the fusion of the head and chest and consisting of durable chitin, and a soft abdomen. On the cephalothorax there are already eight eyes! Do not be surprised, but generally the minimum number of spider's eyes is six, the maximum is twelve.The cephalothorax is connected with the soft abdomen with a very thin and small tube. At the end of the non-segmented abdomen are located the so-called cobweb warts. I will tell you about their purpose below.
How many legs does the spider have?
Many of us still can not properlyanswer the question about how many legs the spider has and probably think that there are six of them, like all insects. But it was not there! This is the main difference - the presence of eight legs, while insects, in fact, only three pairs of legs. The first pair of spider's legs are chelicera. These are poisonous head limbs, which serve to grasp and crush food. Next come three pairs of feet intended for walking.Here we are and we know how many legs a spider, fromwhat departments it consists of, how many pairs of eyes it has and, perhaps most importantly, that it is not an insect! These are its main external features. We pass to the internal "spider review".
The internal structure of the spider
It is a nervous system controlled by the brain,located in the cephalothorax. There is a spider and a heart that is in the upper anterior part of the soft abdomen (red in the figure). Heart beat frequency is 30-70 beats per minute, but if the spider is tense or exhausted for any reason, then this frequency increases to ... 200 beats per minute! At the end of the abdomen are the so-called spinning organs. They produce silk and are associated with glands producing various proteins. As a result of mixing and polymerization of proteins, a thin silk is produced, passing through special spinning organs and turning into a thread. Here it is - cobwebs!Habitat
Spiders are spread all over the world -from Antarctica and highlands to deep gorges and caves. Many of them live on land, and some - in the seas, in fresh sources and in underground waters.