ARACHNIDS

By: John Bamboukian, Tarek Alaeddine, Fawzi Balaa, and Carl Dainel.

=Table of Contents= Introduction:Physiology: Diet and Digestive System:Reproduction: ﻿Mites and Ticks:﻿Spiders: ﻿Obtaining Food:﻿ ﻿Catching the Pray:Killing the Pray: Spider Classification:Fun Facts Scorpions:




 * __Introduction:__ **

Kingdom: Animalia Phylum: Arthropoda Subphylum: Chelicerate Class: Arachnida

Arachnids are a class of joint-legged invertebrates. All of them have eight legs although in some species, the front two may convert to sensory organ. The word "Arachnid" is derived from the greek word "arcane"(aráchnē), meaning spider.

Most arachnids live on land although some may live in fresh water. Spiders, Scorpions, Mites, and Ticks are all examples of Arachnids.

Almost all adult arachnids have eight legs, and they 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, the chelicerae, serve in feeding and defense. The next pair of appendages, the pedipalps have been adapted for feeding, locomotion, and/or reproductive functions. 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 pre-abdomen and post-abdomen, although this is only clearly visible in scorpions, and in some orders, such as the Acari, the abdominal sections are completely fused.

__**Physiology:**__
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. There are some characteristics that are particularly important for the terrestrial lifestyle of an arachnid, such as internal respiratory surfaces in the form of tracheae, or modification of the book gill into a book lung, an internal series of vascular lamellae used for gas exchange with the air. While the tracheae are often individual systems of tubes, similar to those in insects, ricnuleids, pseudoscorpions, and some spiders possess sieve tracheae, in which several tubes arise in a bundle from a small chamber connected to the spiracle. This type of tracheal system has almost certainly evolved from the book lungs, and indicates that the tracheae of arachnids are not homologous with those of insects.

**__Diet and Digestive System:__**
Arachnids are mostly carnivorous, feeding on the pre-digested bodies of insects and other small animals. Only in the harvestmen and among mites, such as the house dust mite, is there ingestion of solid food particles, and thus exposure to internal parasites, 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 and chelicerae. The digestive juices rapidly turn the prey into a broth of nutrients which the arachnid sucks into a pre-buccal cavity located immediately in front of the mouth. Behind the mouth is a muscular, sclerotised 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 is tubular in shape, with multiple diverticula extending throughout the body. The stomach and its diverticula both produce 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.

__**Senses:**__
Arachnids have two kinds of eyes. The lateral and median ocelli. The lateral ocelli evolved from compound eyes and may have a tapetum(an organ that enhances the ability to collect light. The median ocelli evolved from a transverse fold of the ectoderm(the outer layer of the embryo).

In addition to the eyes, almost all arachnids have two other types of sensory organs. The most important to most arachnids are the fine sensory hairs that cover the body and give the animal its sense of touch. These can be relatively simple, but many arachnids also possess more complex structures, called trichobothria.

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 proprioception, and possibly also hearing.

__**Reproduction:**__
Arachnids may have one or two gonads(a reproductive organ that produces sperm or egg cells), which are located in the abdomen. The genital opening is usually located on the underside of the second abdominal segment. In most species, the male transfers sperm to the female in a package, or spermatophore. Complex courtship rituals have evolved in many arachnids to ensure the safe delivery of the sperm to the female.

Arachnids usually lay yolky eggs, which hatch into immatures that resemble adults. Scorpions, however, are either ovoviviparous(where eggs that develop within the female, deriving some nutrition from her but remaining encased within an egg membrane) or viviparous(bearing live young, not eggs), depending on species, and bear live young.

=﻿__**Mites and Ticks:**__= Most mites are animals or plant parasites. All ticks are animal parasites. Mites and Ticks are a group of invertebrates related to spiders. Mites are 1/64 inch to 1/8 inch (0.4 to 3 mm) in length. Some species of mites live on land, others in water. Some are agricultural pests, feeding on crops and the leaves of fruit trees. Other species carry disease-producing microorganisms; one species causes mange in vertebrates. Other species of mites are beneficial, preying on aphid eggs and nematode Ticks live on land, primarily in woods and pastures. Ticks are bloodsucking parasites that can carry disease-producing microorganisms.Diseases carried by ticks include lyme disease and rocky mountain spotted fever.

=__ ﻿Spiders: __= Spiders are animals with eight legs, and chelicerae (pointed appendages) with fangs that inject venom.

__ ﻿Obtaining Food:﻿ __
Most spiders are predators, but scientists have found a vegitarian species called the //Bagheera kiplingi.// As predators, spiders mostly feed on insects and other spiders. Bigger species also feed on birds and lizards. Spiders cannot swallow their food because they have small guts. They need to eat their prey as liquids so that they can swallow it. Spiders have two sets of filters that keep out solid food from entering the gut. Because spiders cannot swallow their food, they release enzymes( A substance tha increases chemical reactins) into their prey's body that turns it into a liquid.

__ ﻿Capturing the Pray: __
Spiders have many strategies to catch their pray. For example trapping it in stick webs, mimicking the prey to avoid detection, or running it down. Most spiders find thier prey by sensing vibrations, but other active hunters have a more acute vision. Hunters from the genus //Portia// show signs of intelligence in their choice of tactics and ability to develope new ones. The most known way for spiders to catch their prey is by using a web. They can capture different insects in the same area. For example, some spiders weave flat horizontal webs to capture insects that fly up from vegitation, and other spiders can also build underwater webs. Other spiders, like the tarantula, are ambush predators. They trick the prey to come to them. To kill the prey, spiders use their fangs to inject venom in them.

__**Defence:﻿**__
Spiders use camouflage to escape from major predators like birds and parasitic wasps. Many spiders from the family of Theraphosidae have hairs on their abdomens and use their legs to flick themselves on the attackers. These hairs are setea with fragile bases and a row of barbs on the tip. The setea causes alot of irritation to the attacker, but their is no evidence that they contain venom.

__ **Spider Classification:** __

 * Kingdom: || Animalia ||
 * Phylum: || Arthropoda ||
 * Subphylum: || Chelicerata ||
 * Class: || Arachnida ||
 * Order: || Araneae ||

**__ Body Plan: __**
Arachnid anatomy: (1) four pairs of legs (2) cephalothorax (3) opisthosoma (abdomen)
 * __ ﻿ __** Since spiders are athropods, they have segmented bodies with jointed limbs, all covered in a cuticle made out of chitin (a long chain of polymer), and heads that are composed of several segments. The foremost one, called the cephalothorax is a complete fusion of the segments segments that in an insect would form two separate tagmata, the head and thorax. the rear tagma is called the abdomen or opisthosoma. In spiders the cephalothorax and abdomen are connected by a small cylindrical section, the pedicel. The pattern of segment fusion that forms chelicerates' heads is unique among arthropods, and what would normally be the first head segment disappears at an early stage of development, so that chelicerates lack the antennae typical of most arthropods. In fact chelicerates' only appendages ahead of the mouth are a pair of chelicerae, and they lack anything that would function directly as "jaws". The first appendages behind the mouth are called pedipalps, and serve different functions within different groups of chelicerates.

**__Locomotion:__**
Although all athropods use muscles attached to the inside of the exoskeleton ﻿to flex their limbs, spiders use hydraulic pressure to extend themselves. If a spider has a punctured cephalothorax (the first section in an arachnid's body), it cannot extend itself. Spiders can generate pressures up to eight times their resting level to extend their legs, and jumping spiders can jump up to 50 times their length by rapidly increasing the blood pressure in the third or fourth pair of legs.

__**Benifits to Humans:**__
Cooked tarantulas are loved food in Cambodia and the for indians of southern Venzuela. Spider venom is a used as a pesticide. It is deadly to insects but not to most vertibrates.

__ Fun Facts: __

 * Spiders are found in every continent exept Antarctica.
 * Spiders have established in nearly every habitat except air and water.
 * Spiders are the largest group of arachnids and the seventeenth largest species in the world.
 * In 2008, taxonomists recorded 40,000 species of spiders and 109 families.
 * The smallest spider in the world, called //Patu digua//, are from Colombia. They measure less than 0.37mm in body
 * length.
 * <span style="background-color: #fc1dd0; font-family: 'Comic Sans MS',cursive;">The biggest spiders are tarantulas. Their body length varies up to 90mm and their legs span up to 250mm.
 * <span style="background-color: #00ffff; font-family: 'Comic Sans MS',cursive;">There were 100 reported deaths of humans by spider bites in the 20th century.
 * <span style="background-color: #808000; font-family: 'Comic Sans MS',cursive;">Funnel web spiders defend them selvez by using agression and venom, but they rarely inject venom. Only 13 known deathes were from this type of spider.

=**__Scorpions:__**= Scorpions are from the class Arachnida; they are closely related to Spiders, Mites, and Ticks. Scorpions have a poison filled stinger at the end of their abdomen that can paralyze its prey. There are over 30000 or 40000 types of scorpions that can kill their prey with the Venom. Scorpions are carnivores that feed on tiny insects, and bugs.

**__Killing its prey:__**
If a scorpion is under attack by its prey, it would spray venom on it. If the scorpion wants to kill its pray undetected, it would sneak up from behind it, jump on it, and then sting it.

**__ Body segments: __**
Scorpions have six body segments and two body openings, the mouth and the anus. The first segment containes the sexual organs, the second segment containes feather like sensory organs, and the four others contain a pair of lungs.

**__ Fun facts: __**
> though they cant see very well.
 * Some scorpions have over ten eyes
 * After mating, the female scorpion becomes aggressive and kills its family.
 * If the mother scorpion gets hungry, it will have her offsprings for lunch and her mate for dinner.

<span style="color: #2524e5; font-family: Tahoma,Geneva,sans-serif; font-size: 150%; margin: 0cm 0cm 0pt 36pt; text-indent: -18pt;">**__ Bibliography: __** http://en.wikipedia.org/wiki/Spider <span style="color: #2524e5; font-family: Tahoma,Geneva,sans-serif; font-size: 150%; margin: 0cm 0cm 0pt 36pt; text-indent: -18pt;">__Britaenica Encyclopedia__ Volume IX Spider (p.420) year 2002 <span style="color: #2524e5; font-family: Tahoma,Geneva,sans-serif; font-size: 150%; margin: 0cm 0cm 0pt 36pt; text-indent: -18pt;">http://en.wikipedia.org/wiki/Scorpion <span style="color: #2524e5; font-family: Tahoma,Geneva,sans-serif; font-size: 150%;">__Britaenica Encyclopedia__ Volume VIII Scorpion (p.990) year 2002