Data Bases • Custom Term Papers • Free Term Papers • Free Research Papers • Free Essays • Free Book Reports • Plagiarism? Links • Top 100 Term Paper Sites • Top 25 Essay Sites • Top 50 Essay Sites • Search 97,000 Papers @ DirectEssays.com • Search 101,000 Papers @ ExampleEssays.com • Search 90,000 Papers @ MegaEssays.com Free Essays • Term Paper Sites • Chuck III's Free Essays • Free College Essays • TermPaperSites.com • My Term Papers • Get Free Essays • Essay World • Planet Papers	Search Lots of Essays Back to Subjects - Animal Science & Zoology Chondrichthyes vs Arthropod Chondrichthyes vs Arthropod The black widow is most easily recognized by the hourglass marking on the underside of its abdomen. When bitten, a neurotoxin is released that can cause dull pain and cramping in muscles, that can be accompanied by sweating and vomiting. Less than 1% of black widow bites result in death. Black widow spiders are usually not aggressive. If disturbed, they will retreat to a corner of their web. These spiders are more aggressive if they are protecting an egg sac. The natural habitat of a black widow is outdoors, under rocks, brush or piles of debris. Indoors, these spiders can usually be found behind furniture, in storage boxes, etc. A black widow's eyes are on top and near the front of its head. They have 8 eyes, arranged in 2 rows of 4 each. Some spiders have better vision than others. For example, hunting spiders have good eyesight at short distances. Their eyesight enables them to form images of their prey and mate. Web-building spiders (the black widow) have poor eyesight. Their eyes are used for detecting changes in light. A black widow's mouth opening is bellow its eyes. It does not have chewing mouth parts, and they eat only liquids. Various appendages around the mouth opening form a short "straw" through which the spider sucks the body fluid of its victim. The black widow can eat some of the solid tissue of its prey by predigesting it. To do this, the spider sprays digestive juices on the tissue. Chelicerae are a pair of appendages that the spider uses to seize and kill its prey. The chelicerae are above the mouth opening and just below the spider's eyes. Each chelicera ends in a hard, hollow, pointed claw, and these claws are the spider's fangs. An opening in the tip of the fang connects with the poison glands. When the black widow stabs an insect with its chelicerae, poison flows into the wound and paralyzes or kills the victim. The fangs of tarantulas point straight down from the head, and the poison glands are in the chelicerae. In the black widow, the fangs point crosswise, and the poison glands extend back into the cephalothorax. They also crush thier prey with their Pedipalpi are a pair of appendages that look like small legs. One pedipalp is attached to each side of the spider's mouth, and they form the sides of the mouth. Each pedipalp has six segments (parts). The segment closest to the body bears a sharp plate with jagged edges. The spider uses this plate to cut and crush its food. In adult male spiders, the last segment of each pedipalp bears a reproductive organ. A spider has 4 pairs of legs, which are attached to its cephalothorax. Each leg has 7 segments. In the black widow, the tip of the last segment has 2 or 3 claws. A pad of hairs called a scopula may surround the claws. The scopula stick to smooth surfaces and helps the spider walk on ceilings and walls. Each leg is also covered with sensitive bristiles that serve as organs of touch and perhaps organs of smell. Some bristles pick up vibrations from the ground or air, or the spider's leg. Others detect chemicals in the environment. When a black widow walks, the first and third leg on one side of its body move with the second and forth leg on the other side. Muscles in the legs make the legs bend at the joints. But spiders have no muscles to extend their legs. The pressure of the blood in their bodies makes their legs extend. If a widow's body does not contain enough fluids, its blood pressure drops. The legs draw up under the body, and the animal cannot walk. Spinnerets are short, finger-like organs with which the spider spins silk. They are attached to the rear of the abdomen. The black widow have 6 spinnerets. The tip of a spinneret is called the spinning field. The surface of each spinning field is covered by as many as a hundred spinning tubes. Through these tubes, liquid silk flows from silk glands in the spider's abdomen to the outside of its body. The silk then hardens into a thread. Black widow's have 2 kinds of breathing organs-tracheae and book lungs . Tracheae are small tubes which carry air to the body tissues. Air enters the tubes through 1 or, rarely, 2 spiracles. A spiracles is an opening in front of the spinnerets. Book lungs are in cavities in the spider's abdomen. Air enters the cavities through a tiny slit on each side and near the front of the abdomen. Each lung consist of 15 or more thin, flat folds of tissue arranged like the blood vessels. As air circulates between the sheets, oxygen passes into the blood. The blood of black widows contains many pale blood cells and is slightly bluish in color. The heart, a long, slender tube in the abdomen, pumps the blood to all parts of the body. The blood returns to the heart through open passages instead of closed tubes, such as those of the human body. If the spider's skin is broken, the blood quickly drains from its body. A digestive tube extends the length of the spiders body. In the cephalothorax, the tube is larger and forms a sucking stomach. When the stomach's powerful muscles contract, the size of the stomach increases. This causes a strong sucking action that pulls the food through the stomach into the intestine. Juices in the digestive tube break the liquid food into molecules small enough to pass through the walls of the intestine into the blood. The food is then distributed to all parts of the body. Food is also pulled through the stomach into a finger-like cavity called the caeca. The ability to store food in the caeca enables spiders to go for long periods of time, over a year in some cases, without eating. The central nervous system of the black widow is in the cephalothorax. It includes the brain, which is connected to a large group of nerve cells called the gandlion. Nerve fibers from the brain and gandlion run throughout a spider's body. The nerve fibers carry information to the brain from sense organs on the head, legs, and other parts of the body. The brain can also send signals through the nerve fibers to control the activities of the body. The great white shark is a ferocious predator. This species of shark comes in a variety of sizes, but average about 4.3 to 5.5m. Roughly they weigh about 680 to 1,800kg. The great white shark is equipped with extraordinary senses. They primarily use their sense of smell, followed by their sensing of electric charges. Other senses such as eyesight, sensing changes in water pressure and hearing are seldom used. the great white's nostrils can smell a single drop of blood in 25 gallons of water. The sensing of minute electrical discharges in the water is accomplished by a series of jelly-filled canals in the head called the ampullae of Lorenzini. This allows the shark to sense the tiny electrical fields generated by all animals, for example, from muscle contractions. It may also use this to detect magnetic fields which some sharks may use in navigation. To compliment its senses, it is also an amazing swimmer. Equipped with a stream-lined body which allows it to may reach speeds of up to 40 mph. It has 3 primary fins, the dorsal fin(on its back) and 2 pectorial fins; however the great white shark does not use these while swimming. It swims by propelling itself through the water by using its tail. One negative aspect of the shark is its inability to bend its pectorial fins backward. This prevents it from stopping suddenly or swimming backward. A shark must keep swimming or it will sink. Perhaps the most feared part of the great white is its mouth. The sharks mouth is supplied with a huge amount of teeth at one time(up to 3,000). They are triangular, serrated, razor-sharp and up to 3in long. These teeth are located in several rows which rotate into use as needed. The first two are used in obtaining prey. As this teeth get worn of break, some from the back rows rotate into the front. The great white is usually found near shore lines along most of the temperate coastlines around the world. These solitary animals have been observed along the coastlines of California to Alaska, the east coast of the U.S.A. and most of the Gulf coast, Hawaii, most of South America, South Africa, Australia, New Zealand, the Mediterranean Sea, West Africa to Scandinavia, Japan, And the eastern coastline of China and Southern Russia. The Great white shark gets in name from the long white belly, but the rest of the fish is a grayish color. This helps when stalking prey. It hunts below its prey enabling it to blend in with the water. Most sharks swallow their food whole of bite it into relatively large pieces. The great white has a U-shaped stomach that use very strong acids and enzymes to dissolve most of what is eaten. The stomach produces an easily absorbed soupy mush. Only this liquid mush enters the intestines because the pyloric valve (the valve between the stomach and the intestines) is small. Indigestible things, like very large bones and non-nutritive items, are vomited. Absorption of nutrients takes place in the intestines. Although the intestines are short, they have a large surface area due to infolding of the inner surface of the intestines. Some shark intestines ate arranged in folds, some are in spiral pattern, like a spiral staircase enclosed in a cylinder. After absorbing the nutrients from the food, the waste leaves the body through the anal fin (which is located on the underbelly of the shark.) Although the great white has nostrils, it does not use them to breathe. The shark has 5 gills on its side which it uses to breathe. The shark takes in water and filters out the oxygen then the water is released, out of the body. Unlike most bony fish, shark's eggs are fertilized inside the female's body. The male shark had "claspers" extensions of the pelvic fins that are used to transfer sperm to the female and fertilize her eggs. Great white sharks are ovoviviparous; they give birth to 2-14 fully formed pups that are up to 5ft long. The eggs hatch within the female and are nourished by eating unfertilized eggs and smaller siblings in the womb. There is no placenta to nourish the babies-they must fend for themselves even before birth. They swim away from the mother immediately after birth, there is no maternal care given. All of the sharks body systems are completely different from that of the spider. The digestive system, for example, of the shark allows it to swallow food whole; or at least a large fraction of that, while that of the spider prevents it even eating its prey. All the spider is capable of is literally "sucking" out its preys life. However the black widow is a good mother. Once it lays its eggs, she protects them aggressively. While on the other hand the great white shark never cares for her young. Although both have different ways of catching prey, both are effective. The black widow builds traps and awaits a victim, while the shark relies on its keen sense of smell. Referring back to the first argument (the digestive system) the black is able to store food away for a time of need, while the shark, not concerned with food supply, takes the bare necessities. Although both these animals are very different they are also very alike. Both of these animals are best suited for their environment. Review again the above information about the black widow and the great white shark, and ponder. Think about the environment it lives in and each detail about the animal will make sense. Bibliography: Word Count: 2049
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