The anatomy of spiders includes many characteristics common to other arachnids. These characteristics include parts of the body that are divided into two segments, eight legs connected, without wings or antennae, the presence of chelicera and pedipalps, simple eyes and an exoskeleton, which is periodically reset.
Physical features of spiders
Arachnids, the higher cheliceric arthropods, are often called insects, but this is not true. Not only do their legs and body segments make them different, but unlike insects, arachnids do not have wings, cannot chew, and they do not have antennas. A spider has several body features that help them do some pretty amazing things. Since all spiders are predators, they have fangs that they use to paralyze or kill their prey - chelicerae, and pedipalps in males to transmit seminal fluid to the female.
Spiders have no teeth, so they cannot chew or swallow. The poison in their fangs not only paralyzes, but also liquefies the insides of the victim, which become the food of the spider. Spiders have things called spinners that produce silk. This silk is used by spiders to build their homes, catch prey for food, hide, protect their children and help them make their first journeys. Their bodies are also coated with oil, which prevents them from getting stuck on their silk, like their prey.
Arachnids
Spiders belong to the class of arachnids, which are animals with eight legs and two parts of the body. There are about 40,000 known species, and they live on every continent of the Earth. Spiders also have several devices that distinguish them from other arachnids.
All spiders are capable of producing a web-creating substance to lure prey. Most spiders contain poison, which is introduced into the prey through the chelicera fangs. Male spiders have specialized pedipalps that are used to transmit sperm to the female during mating. Many species of spiders exhibit great sexual dimorphism.
Modifications of chelicera and pedipalp in arachnids
The body of the arachnids includes the cephalothorax, carrying 6 pairs of limbs, and the abdomen. Two front pairs are adapted to capture and grind food - they are called chelicerae, and pedipalps, which also help to knead and grind food. The former are located in front of the oral cavity and often look like short claws.
Arachnid chelicera, as a rule, consist of 3 segments, the end segment performs the task of a moving claw finger. In rare cases, chelicerae can end with a moving tool in the form of a claw or in the form of two-part appendages with a sharply jagged edge, with which you can pierce the integument of the victim.
The extremities of the second pair, called pedipalps, consist of several segments, on the main of which there is a special chewing outgrowth that helps knead food. The remaining segments look like tentacles. For example, the pedipalps of scorpions are represented by powerful long claws, in some spiders they look like ordinary paws.
Features of the nervous system Arachnida
The arachnid nervous system is due to the complex structure of the brain, consisting of 2 sections:
- Anterior prototserebrum innervating the eyes.
- The posterior tritotserebrum, which sends nerves to the chelicerae.
Sensory organs
Very important organs in arachnids are chelicera and pedipalps. On the latter there are a large number of sensitive hairs that respond very quickly to various tactile irritations. These hairs are called trichobotria, in addition to pedipalps, they are also on the legs and surface of the body. Trichobotria are needed to capture air vibrations.
In addition to the chelicera and pedipalps of the spider, there are other sensitive organs - organs in the form of a lyre for chemical sensation and smell, as well as eyes, the amount of which depends on the species. They can be 12, 10, 8, 6, very rarely 2. As a rule, spiders have four pairs of simple eyes, and of different sizes, some larger, others smaller.
Sophisticated oral apparatus
The arachnid's oral cavity is equipped with chelicera, as already mentioned, this is the first pair of head limbs in arthropods. What are they needed for? Since they are an integral part of the oral apparatus, their main task is to chop, grind or puncture food. Appearance depends on the type of animal, chelicera can be like claws, hooks or needles. These features depend on the type of oral cavity.
Here are some types of mouthparts:
- Gnawing (barn ticks). Chelicera are large and similar to claws.
- Stitching-sucking (ticks, the diet of which includes plants or animal blood). Chelicera, respectively, have a thinner form, without teeth, resembling a hollow tube.
In spiders, chelicerae have a terminal segment in the form of a claw, on which the duct of the poisonous gland opens.