Arachnids

= Arachnids = **//ARACHNIDS 101.//** Kingdom: Animalia Phylum: Chordata​ SubPhylum: Chelicerata Class: Arachnida // ** /!\ Spiders are arachnids, but not all arachnids are spiders ! ** //

Arachnids are members of a class of animals that includes spiders, scorpions, mites, and ticks. What they all have in common—and what distinguishes them from insects—are four pairs of legs and no antennae.

__**Anatomy**__ Almost all adult arachnids have four pairs of legs, and arachnids can be difrenshiated easily from insects for one reason, since insects have six legs. Arachnids also have two further pairs of appendages that have become adapted for feeding, defense, and sensory perception. The first pair, the chelicerae, serve in feeding and defense. The next pair of appendages, the pedipalps have been adapted for feeding, locomotion, and/or reproductive functions. In Solifugae, the palps are quite leg-like, so that these animals appear to have ten legs. The larvae of mites and Ricinulei have only six legs; the fourth pair appears when they moult into nymphs. However, there are also adult mites with six, or even four legs. Arachnids are further distinguished from insects by the fact they have no antennae or wings. Their body is organized into two tagma called the prosoma, or cephalothorax, and the opisthosoma, or abdomen. The cephalothorax is derived from the fusion of the cephalon (head) and the thorax, and is usually covered by a single, unsegmented carapace. The abdomen is segmented in the more primitive forms, but varying degrees of fusion between the segments occur in many groups. It is typically divided into a preabdomen and postabdomen, although this is only clearly visible in scorpions, and in some orders, such as the Acari, the abdominal sections are completely fused. Like all arthropods, arachnids have an exoskeleton, and they also have an internal structure of cartilage-like tissue called the endosternite, to which certain muscle groups are attached. The endosternite is even calcified in some Opiliones

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** Arachnids are mostly carnivores, feeding on the pre-digested bodies of insects and other small animals. Only among mites and other arachnids, there is ingestion of solid food particles. Although it is not unusual for spiders to eat their own silk. Several groups secrete venom from specialized glands to kill prey or enemies. Several mites are parasites, some of which are carriers of disease. Arachnids pour digestive juices produced in their stomachs over their prey after killing it with their pedipalps, which are part of their mouths and chelicerae, which are different pair of legs. The digestive juices rapidly turn the prey into a sort of soup or mix of nutrients which the arachnid sucks into a cavity located immediately in front of the mouth. Behind the mouth is a muscular pharynx, which acts as a pump, sucking the food through the mouth and on into the oesophagus and stomach In some arachnids, the oesophagus also acts as an additional pump. The stomach and produces digestive enzymes and absorb nutrients from the food. It extends through most of the body, and connects to a short sclerotised intestine and anus in the hind part of the abdomen. ** ====== Orders: taleed maamari Ø Acarina Ø Amblypygi Ø Araneae Ø Haptopoda Ø Opiliones Ø Palpigradi Ø Phalangiotarbida Ø Pseudoscorpions Ø Ricinulei Ø Schizomida Ø Scorpions Ø Solifugae Ø Trigonotarbida Ø Thelyphonida

__**Rerproductive System Mark Eke :**__ Arachnids may have one or two gonads, which are located in the abdomen. The genital opening is usually found under the second abdominal piece. In most species, the male transfers sperm to the female in a package, or [|spermatophore]. Many ways have been developed to ensure the safety of sperm transfer between the two sexes. Arachnids usually lay yolky eggs, which hatch into immatures that resemble adults. 1) The male deposits spermatophore on the ground during the “dance.” 2) He then positions the female over the spermatophore. 3) Embryos are then brooded within the female and birth is in the process. 4) After hatching, most baby arachnids stay with the mother, riding on their back for several years.

__Elias__ __body of arachinids:Almost all adult arachnids have four pairs of legs, and arachnids may be easily distinguished from insects__ __by this fact, since insects have six legs. However, arachnids also have two further pairs of appendages that have become adapted for feeding, defense, and sensory perception. The first pair, thechelicerae, serve in feeding and defense. The next pair of appendages, the__ pedipalps __have been adapted for feeding, locomotion, and/or__ r__reproductive functions. In solifugae____, the palps are quite leg-like, so that these animals appear to have ten legs. The larvae of mites and recinulei have only six legs; the fourth pair appears when they__ moult __into nymphs__ __However, there are also adult mites with six, or even four legs.Spiders have 2 fangs for eating and paralyzing prey.Black widows have a lined web stuck to the ground for catching ground prey..__ **//__Marc Akoury Senses__//** Arachnids have two kinds of eyes, the lateral and median ocelli. The lateral ocelli started from compund eyes and may have a tapetum, which allows the abillity to collect light. The ancestors of modern arachnids probably had both types, but modern ones often lack one type or the other. The cornea of the eye acts like lends .Beneath this is a transparent vitreous body. In most arachnids, the retina probably does not have enough light sensitive cells to allow the eyes to form a proper image. In addition to the eyes, almost all arachnids have two other types of sensory organs. The most important to most arachnids are the sensory hairs that cover the body and give the animal its sense of touch. These can be simple, but many arachnids also possess more complex structures, hcalled tricobothria. Finally, slit sense organs are slit-like pits covered with a thin membrane. Inside the pit, a small hair touches the underside of the membrane, and detects its motion. Slit sense organs are believed to be involved in hearing.

Ocelli: a type of simple eye common to invertebrates, consisting of retinal cells, pigments, and nerve fibers. Tapetum: // Botany //. a layer of cells often investing the archespore in a developing sporangium and absorbed as the spores mature. Cornea: the transparent anterior part of the external coat of the eye covering the iris and the pupil and continuous with the sclera. Vitreous: obtained from or containing glass.

Because they are small, spiders have many enemies. Larger animals, such as birds, toads, lizards and monkeys, hunt them. But they are also used as food by many smaller creatures. Ticks will attach themselves to a spider and eat away at it for a long time while the spider goes about its business. One of the spider’s worst enemies is the Spider-Wasp. The female wasp will paralyze the spider by stinging it. Then she digs a hole and puts the spider and an egg into it. When the egg hatches, the baby wasp will eat away at the paralyzed spider. Humans are also enemies of spiders. Besides stepping on them, the pesticides we use to control other insects can kill spiders.

There are many needed to know things that are in a way important for the terrestrial lifestyle of an arachnid, such the inside respiratory surfaces in the form of lamelle used for gas exchange with the air. While the tracheae are mostly in a single systems of tubes, as of those in insects, ricnuleids, pseudoscorpions, and some spiders hold sieve tracheae, in many tubes rise in a bundle from a tiny chamber attached to the spiracle. This kind of tracheal system has nearly for sure grew strongly from the book lungs, and shows that the tracheae of arachnids are not homologous with those of insects.  Newer adaptations to terrestrial life are appendages were checked for faster movement on land, inside fertilisation, special sensory organs, and water conservation well developed by efficient excretory structures as well as a waxy layer protecting the cuticle. The excretory glands of arachnids have up to 8 coxal glands along the one of the sides of the prosoma.


 * Extra Questions: ||
 * 1. Name __two__ parasitic arachnids. ||
 * 2. How do parasitic arachnids get food from their host? ||
 *  3. Name __two__ human diseases caused by parasitic arachnids ? ||

Answers to the Extra Questions: Taleed Maamari

1) chigger (mite) and scabies (mite) 2)the chigger attaches to the skin and inject a substance that creates a liquid nutrients by dissolving and liquefying the skin cells. The host’s immune system responds by trying to create a barrier between the affected cells and healthy cells – a tiny hole called a stylostome forms in the skin with the larva in the center, still drawing liquefied food from the tissues below the bite as though sucking through a straw 3)mange and scabies are diseases from parasitic arachnids.

[|Parasites - humans, examples, body, water, process, life, plants, type, form, methods, animals, system, parts, cause, primary, surface] []

Mange is a skin desease found in many mammals and is caused by a mite that burrows beneath the skin. Most people are familiar with mange  because of its presence in their pets, often cats and dogs. There are a variety of mange mites , but only a handful of them affect pets. Mange mites themselves cannot be seen with the naked eye, but the effects of their burrowing can be very dramatic. Some types of mange  look like dandruff, but the effects are often short-lived. Different types of mange  include: notoedric mange, sarcoptic mange , and demodectic mange.