Medical Significance of the Class Arachnida Arthropoda : The class Arachnida is a group of more than 100,000 species, including spiders, scorpions, ticks, and mites. Most arachnids are adapted to kill prey with poison, stingers, or fangs. Like crustaceans, arachnids have a body that is divided into a cephalothorax and abdomen.
On the cephalothorax there are 4 pairs of legs, a pair of Chelicerae, and a pair of appendages called the pedipalps. The pedipalps help chew; in some species the pedipalps are specialized to perform other functions. Arachnids undergo incomplete metamorphosis. The class Arachnida includes 3 orders of medical importance:
1. Order the Scorpion
2. Order Araneae (spiders)
3. Order Acari (fleas and mites)
Scorpions are a group of arachnids whose pedipalps are modified into pincers. Scorpions use these pincers to handle their food and tear it apart. The scorpion’s venomous sting is used primarily to electrocute its prey and less often to defend itself. The sting is located in the terminal segment of the body, which is slender towards the tip.
The scorpion’s elongated, jointed belly is its trademark; in most chelicerates, the abdominal segments are more or less fused together and appear as a single unit. Adults of this arachnid order range in size from 1 to 18 centimeters. There are about 1,200 species of scorpion, all terrestrial, living around the world, although they are common in the tropics, subtropics, and deserts.
The mating of scorpions is complicated, with the spermatophores fixed to the substrate by the male and then taken up by the female. The young are born alive, with 1 to 95 in a given liter. Scorpions differ from spiders in two ways. Scorpions have very large pedipalps, which they hold in a forward position.
They also have a large stinger in the last segment of the abdomen. Most scorpions hide during the day and hunt at night. Scorpions catch their prey with pedipalps like pincers. Then the fangs inject a paralyzing venom, the chelicerae tear the prey, the animal is swallowed, and digestion begins. Only a few species have stingers that can become fetuses for humans. They do not sting humans unless attacked.
Local symptoms of the bite include severe pain, inflammation and swelling. Sweating, nausea and vomiting are common systemic symptoms. Muscle spasms and spasms may occur in severe cases. The fatal outcome is due to respiratory failure, pulmonary edema and shock.
There are about 25,000 species of named spiders (order Araneae). These animals play a major role in all terrestrial ecosystems, where they are very important as predators of insects and other small animals. The spider hunts its prey or catches it with a web. Silk webs are formed from liquid protein forced out of the spinnerets, modified appendages on the posterior part of the spider’s abdomen.
Spiders have venom glands leading through their chelicerae, which are pointed and used to bite and immobilize prey. Some members of this order, such as the black widow spider (Latrodectus mactans), Australian black widow spider (Latrodectus seville), caracurt (Latrodectus tredicimguttatus), brown recluse (Loxosceles reclusa), tarantula (Lycosa singoriensis), have a poisonous bite. . . for humans and other large mammals.