Spiders - What Are They?

 Sometimes frighten us by their appearance. Their very thin, long legs and hairy body looks like a monster. These fantastic animals are spiders. Spiders belong to the largest branch of the animal kingdom and arthropod class Arachnida. Spiders have eight legs and chelicerae well developed turned into fangs to inject venom into the victim. They breathe air. Spiders, together, make up the largest population of arachnids and rank seventh in the number of species in the world compared to other organizations. It is a cosmopolitan distribution, but is missing in Antarctica. They do not colonize in the sea and air. In 2008, there were 40,000 taxonomists families and 109 species of spiders, but confusion still prevails on this classification as what has been done this recording and if all species are classified correctly or not.
The body of the spider plan differs from that of other arthropods are divided into two tagmata, cephalothorax and abdomen, and the two are connected by a small stem structure. Lack antennae as insects. A primitive group of spiders called Mesothelae was a well developed nervous system compared to all other arthropods are composed of a large ganglion in a molten mass in the cephalothorax. The spiders have no extensor muscles in their limbs and use of hydraulic pressure to the extension of their members.
The abdomen well developed and has appendages modified using chains named as the production of silk six different types of silk glands embedded within the abdomen. Webs are very different in shape, size, and the mountain of silk thread used for its construction. In 2008 were discovered a vegetarian spider species, but the rest of the species are predators that feed on insects, spiders and some large species, as previously on birds and lizards. Spiders fit various techniques surprising to capture prey like trap prey in sticky web, also show mimicry. Most species catch prey by sensing vibrations, but the genre Portia spiders have well-developed sense of vision. The intestine of spiders is very narrow and therefore are not able to take solid food. They mix the food with the help of digestive enzymes and grind the food with pedipalps because they have true jaws.
Male spiders use fascinating courtship rituals to avoid being eaten by the female spiders. The males have a short life and die after a couple of pairs. The females lay their eggs in the case of silk and each case is home to hundreds of eggs. The females of some species also show parental care for eggs. The social organization has been noted in some species, like the widow who make a huge web containing about 50,000 individuals. Most species have a life span of about two years, but tarantulas and mygalomorphs live up to 25 years in captivity.
Spider venom is harmful to humans and the search continues to make use of spider venom in medicine and non-polluting pesticides. Spider silk is a good source of resistance, lightness and is much higher than that of synthetic materials. They are also a symbol of terror and cruelty in mythology. Are chelicerates and body like other arthropods has been divided into segments carrying covered by the cuticle and jointed appendages consisting of chitin and other proteins. The head consists of a large number of segments that come together in the embryo. Are coelomates and coelom is reduced to a small area around the excretion and reproductive organs. The position of the coelom is mainly taken by the hemocoel, a cavity which extends over the entire length of the body and the blood flowing through it. The core is in the form of a tube in the upper part of the body composed of a few ostia that act as non-return valves. Spiders have open circulatory systems. Many books have spiders lungs and carries a respiratory pigment keyhole for the transport of oxygen. Breathing can be performed by the system book-lung or trachea. Tracheas in spiders are effective bodies of water conservation and maintain a better metabolic rate.
Spiders excrete their waste product in the form of a nitrogenous waste denominated as uric acid, which leaves the body in the form of a solid. Excretory organs are Malpighian tubules that help pass uric acid through the anus. The general plan of the central nervous system in spiders consists of the brain formed by the fusion of the nuclei within the carapace, and the strings mouth and nerve arising from the nodes. The most spiders are four pairs of eyes in the front of the carapace, and also wear cups of pigments called eyespots that help in the detection of light. The eyes are responsible for vision mosaic because they are the compound eyes. There are a large number of hairs or bristles throughout the body that act as receptors tactile and taste. The spiders were not well developed in the muscles of the limbs so they move with the help of hydraulic pressure. If the carapace of a spider is damaged, is unable to move his legs. Spiders can generate a pressure of more than eight times to stretch their legs and jumping spiders can jump 50 times their length with hydraulic pressure.
Spider silk is produced by silk glands present in the abdomen, and is similar to that of silk insect. It is essentially a protein that is generally flexible, but hardens on exposure to air. It seems nylon, the collagen in its tensile strength. Spiders reproduce sexually and fertilization is internal, but indirect. The females are oviparous and lay their eggs in about 3000 bags of silk egg that are maintained at a particular level of humidity. The females of some species die after spawning, but most of the species to protect their eggs by attaching them to their nests or other means. The baby spiders spend their larval stages in the egg sac ad hatch as small, sexually immature spiders race.
Three classes of pigments were identified in spiders and include, ommochromes, bilins and guanine. Many spiders use camouflage as a defensive measure. Some species of spiders also show social behavior. Scientists believe that spiders have developed 100 million years. Spider bites are responsible for a series of symptoms such as headache, redness, pain, itching, shortness of breath, muscle cramps, etc. Some spiders are also a source of delight for the residents of some countries. Tarantulas are cooked and eaten by some people.