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ANIMALS (Part 1 of 4)   Leave a comment

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DEFINITION: 1 any living organism, excluding plants and bacteria: most animals can move about independently and have specialized sense organs that enable them to react quickly to stimuli: animals do not have cell walls, nor do they make food by photosynthesis 2 any such organism other than a human being, esp. a mammal or, often, any four-footed creature 3 a brutish, debased, or inhuman person 4 [Colloq.] a person, thing, concept, etc. thought of as a kind or type [today’s athlete is another animal altogether]

All living things are divided into two main kingdoms the animal and plant kingdoms and two or three other kingdoms that include bacteria, blue-green algae, and one-celled creatures with definite nuclei. What is the difference between a horse, for example, and grass? A horse moves about in the pasture eating grass. It trots toward you when you offer it a lump of sugar and shows pleasure when you stroke its head. The grass, however, is rooted to one place. It does not respond behaviourally to people or to the horse in any way.

Animals Move About and Sense Surroundings

Adult animals move freely from place to place during at least one phase of their life. Plants usually cannot move unless a force, such as the wind, causes them to move.

Most animals move freely from place to place and can sense their surroundings; that is, they can taste, smell, hear, see, and touch. Certain simple animals, such as the corals and barnacles, spend most of their lives fastened to one spot, but they are able to swim freely when they are young. Even these rooted animals have parts that move in order to capture food. Plants, however, cannot shift about at their own will. They react to heat, light, chemicals, and touch, but their responses are involuntary and automatic, quite different from those of animals.

All living things are made of cells. The walls of plant and animal cells are different.

Cellulose, complex carbohydrate consisting of 3,000 or more glucose units; basic structural component of plant cell walls; 90% of cotton and 50% of wood is cellulose; most abundant of all naturally occurring organic compounds; indigestible by humans; can be digested by herbivores, such as cows and horses, because they retain it long enough for digestion by micro organisms present in their digestive systems; also digestible by termites; processed to produce papers and fibres; chemically modified to yield plastics, photographic film, and rayon; other derivatives used as adhesives, explosives, thickening agents, and in moisture-proof coatings.

All living things are made up of cells of protoplasm. They may consist of a single cell, as does an amoeba, or billions of cells, as do trees and horses. The cell wall of a plant is composed of a woody material called cellulose. No true animal contains cellulose. Animal cells are bounded by a membrane composed chiefly of fat and protein.

Green plants make their own food. With the aid of the green substance called chlorophyll, they use the energy in sunlight to change carbon dioxide and water into carbohydrates and other food materials. No true animal contains chlorophyll.

Animals must eat, either directly or indirectly, the food manufactured by members of the plant kingdom. A horse cannot stand in the sun and wait for its body to make fat and proteins. It must move about the pasture in search of green grass. Even meat eaters for example, lions live on animals, such as zebras, which in turn subsist on plants.

The Variety of Animal Life

More than a million different kinds of animals inhabit the Earth. The exact number is not known, for new kinds are continually being discovered. They live in the seas, from the surface down to the black depths where no ray of light penetrates. On mountaintops and in deserts, in mud and in hot pools some form of animal life may be found.

Animals are infinitely varied in form, size, and habits. The smallest animals are bits of protoplasm that can be seen only with a microscope. The largest, the blue whales, may be more than 100 feet (30 meters) long and weigh 300,000 pounds (136,000 kilograms).

Some of the most familiar animals, such as dogs, birds, frogs, and fish, have a backbone and a central nervous system. They are called vertebrates, meaning animals with backbones. Animals without backbones are called invertebrates and include arthropods, worms, molluscs, and many other groups. Most of the vertebrates and many invertebrates have a head where sense organs are concentrated and have legs, wings, or fins for locomotion. Vertebrates and many invertebrates, such as the arthropods and worms, have bilateral, or two-sided, symmetry. This means that they have two mirror-image sides (a right side and a left side), distinct upper and lower surfaces of the body, and a distinct front and rear.

Some invertebrates, such as jellyfish, sea anemones, and starfish, display radial symmetry, in which the parts of the body are arranged around a central axis, similar to a wheel. Animals with radial symmetry live in marine or freshwater aquatic environments. Some drift with the currents, unable to swim in any definite direction. Others become attached to a solid object by one end and float with the mouth end upright. Tentacles arranged in a circle around the mouth sweep in food particles and ward off enemies.

One-celled animals called protozoans live in fresh and salt water. Many are shapeless creatures and cannot swim toward their food. They move along by squeezing out a finger like projection from the body. This is called a pseudopod, from the Greek meaning “false foot.” The pseudopod fastens to something solid, and the rest of the body flows into the fastened projection. The amoeba also moves in this manner. One-celled animals are very small. They are single blobs of liquid enclosed in a thin membrane and as such cannot attain a large size or a very definite shape.

Animals with Outside Skeletons and Feet

Molluscs have soft bodies that are not divided into specialized sections such as head, thorax, and abdomen. Many molluscs are enclosed in hard, hinged shells. Snails have a single large, fleshy foot located on the stomach side.

The heads of the octopus and the squid are surrounded by a circle of eight or ten tentacles that act as arms and feet. Oysters, clams, mussels, and scallops all have a single axe-shaped foot which they burrow into sand.

Most molluscs do not move around efficiently. Oysters fasten themselves to something solid and settle down for life, letting food drift to them. Scallops may move in zigzag leaps by clapping their shells together.

Joint-Legged Animals

Arthropod, animal of the phylum Arthropoda comprising invertebrates with external skeleton, segmented body, and jointed appendages.

Joint-legged animals, or arthropods, have bodies divided into segments that have specialized functions. These animals also have many jointed legs. Most arthropods are covered with a jointed skeleton made of a horny material. This outside skeleton is lighter than the shells of the molluscs The legs and muscles and many organs of the arthropod are attached to the outside skeleton.

The arthropods include insects, lobsters, crabs, centipedes, millipedes, scorpions, and spiders. They can run, jump, swim, and crawl. Some live mostly on land, while others live mostly in water. Many of the insects have wings and can fly. Arthropods inhabit most of the Earth’s environments, from the poles to the tropics, and are found in fresh and marine water and in terrestrial habitats.

How Back boned Animals Move

Vertebrates move through water and air and over the ground with great speed and skill. Birds, with their feathered wings, are the best fliers. Fish are the best swimmers. However, other vertebrates also can fly and swim. Bats fly on wings of membrane like skin. The flying squirrel glides on a broad membrane between its legs. The flying fish soars over the surface of the ocean by using its fins. Neither the fish nor the squirrel can soar great distances, however.

Some turtles swim with paddle like front legs. Some water birds can swim underwater with their wings. The mud skipper and walking catfish are fishes that walk on mud by pulling themselves along on their front fins.

Frogs, kangaroos, various cats, and some fishes are superior jumpers. Salmon leap up waterfalls when they travel from the sea to their home streams to lay their eggs. Tarpon, swordfish, and sailfish make great leaps out of the water when pursuing their prey or trying to escape an enemy.

Breathing

Animals breathe in different ways:

  • Some animals, like amoeba and sponges, let oxygen move through their cell walls.

  • Fish and tadpoles breathe with their gills.

  • Insects bring air in through pores, or holes, called spiracles.

  • Mammals, birds, and reptiles breathe with lungs.

All animals must take in oxygen in order to change food into a form that the body can use. One-celled animals that live in water absorb oxygen directly through their membranes. The sponge is a very simple many-celled animal. The surface of a sponge is covered with millions of tiny pores. Water bearing dissolved oxygen and minute food particles flows through the pores and out of the opening at the top of the sponge.

Fish and tadpoles breathe by means of gills. Insects and caterpillars take air into the body through breathing pores called spiracles.

Mammals, birds, and reptiles obtain oxygen from the air. They take it into the lungs, and the oxygen passes through membranes in the lungs into particles called red blood cells. The bloodstream then carries the oxygen to all parts of the body. Amphibians have lungs, but they also have thin, moist skins that absorb oxygen directly.

Reproduction

Sea squirt, a tunicate or saclike marine animal, so called from its habit of ejecting water when touched; belongs to the phylum Chordata.

Hydra, primitive water animal of the class Hydrozoa and the genus Hydra.

All animals reproduce their own kind. One of the most primitive forms of reproduction is by fission, in which the individual organism divides to produce a replica of itself. Some animals, such as sea squirts, reproduce by budding: lumps appear along a branchlike organ and develop into young sea squirts. Sea squirts, sponges, corals, and other creatures that bud often remain together and form large colonies. The hydra also reproduces by budding, but in time the young bud separates and goes off to live alone.

Most animals reproduce by means of eggs from the female that are fertilized by sperm from the male. The eggs of some species are deposited in a nest or in some other manner before hatching. Most species of mammal and some species of reptile and fish bear their young alive, the fertilized eggs being retained within the body of the female.

The types of reproductive behaviour among animals are almost as varied as the kinds of animals themselves. Some species, such as most insects and turtles, deposit their eggs and give them no further attention. In colonies of the social insects, such as ants and bees, a single female lays all of the eggs, and workers provide care and nourishment for the developing young in the nest. The females of some reptiles, such as the king cobra and the blue-tailed skink, and amphibians, such as the marble salamander, stay with their clutch of eggs until they hatch but provide no protection or nourishment for the young. Some fish guard their young after they are born. Crocodilians protect the eggs before hatching and the young for several months afterwards. Many birds provide not only protection but also nourishment for the developing young. Mammals, which feed their young with milk produced by the mother, provide care for their young much longer than do other classes of animals.

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Posted 2012/01/29 by Stelios in Education

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ANIMALS (Part 2 of 4)   Leave a comment

Homes

Many animals build temporary or permanent homes for themselves and their young. Birds occupy their nests only while they are incubating eggs and feeding the helpless nestling’s A few fish make temporary nests for their young.

No animal dwelling has excited more wonder and interest than the lodge built by the beaver. Almost as remarkable is the dome-shaped winter home of the muskrat. Underground burrows with sleeping rooms, food-storage rooms, connecting tunnels, and emergency exits are constructed by ground hogs, prairie dogs, European rabbits, gophers, kangaroo rats, and field mice. Chimpanzees and gorillas build temporary nests and sleeping platforms of sticks in trees. The living quarters made by the different kinds of ants can be intricate and complex. Certain tropical bats cut palm fronds in such a way that they droop to form a leafy shelter from the hot sun and torrential rains.

Defences

All animals have some means of defending themselves against enemies. A cat can usually outrun a dog and climb the nearest tree. If cornered, it will scratch and bite.

Moose, largest member of the deer family; called elk in Europe.

Many animals rely on speed, camouflage, teeth, claws, and even intimidation to escape other animals. The variety of means of protection is extensive. Porcupines and hedgehogs roll into a ball and raise their sharp quills. The quills come off and stick into the nose or paw of an unwary dog or some other enemy. Skunks spray a foul-smelling fluid from a gland when they are frightened. Deer, moose, and antelope fight with their antlers. An elephant’s trunk is a powerful weapon. It can be used to pick up another animal and smash it to the ground.

Squids shoot out a cloud of inky material and escape under its cover. Torpedo fish and several other kinds of fish have built-in electric storage cells by which they can deliver a paralysing shock. Some insects, snakes, and lizards protect themselves with their venom. Many amphibians produce poisonous skin secretions.

Many animals hide by means of protective colouration A baby deer is almost invisible in the forest because its spotted coat looks like patches of sunlight in the brown leaves. Many fishes, birds, insects, lizards, and snakes use nature’s camouflage to avoid being seen.

Feeding Behaviour

Vorticella (popularly called bell animalcules), genus of bell-shaped Protozoa.

Heliozoan, any protozoan of the order Heliozoa; often called sun animalcule; a single pseudopod may engulf food or several may work together.

Cilia (plural of cilium), hairlike, vibratory appendages found in some plants and animals.

Many one-celled animals (the vorticella and collar flagellate, for example) live in water. These very tiny animals and their feeding habits can be studied only under a microscope. They feed on even tinier organisms in the water. The vorticella is attached by its stalk to some solid object. At the upper end is a mouth surrounded by tiny hairs called cilia. The hairs sweep food particles into the mouth by setting up a whirlpool action in the water. The food is enclosed in a bubble called a food vacuole, where it is digested.

Flagellum (plural flagella), a whip like extension of certain protozoans.

The collar flagellate has a delicate, transparent collar. From the centre of it grows a whip like organ, the flagellum. The beating of the whip draws a current of water toward the cell. Food particles in the current pass through the wall of the cell into the food vacuoles.

The heliozoan, also called sun animal, moves about and captures food by means of pseudopodia. In this case the pseudopodia are stiff spines that radiate from the centre of the cell. The spines wrap around the food and enclose it in a vacuole.

Hydra, primitive water animal of the class Hydrozoa and the genus Hydra.

The hydra feeds most commonly on the larva of a kind of shellfish. It has a mouth surrounded with long tentacles. The tentacles sting and paralyse the prey and then shove it inside the mouth.

Common swallow (in North America, barn swallow), bird (Hirundo rustica).

Butterflies and moths have tube like mouth parts. With these they suck nectar from flowers. Grasshoppers and beetles have chewing, grasping, and tearing mouth parts

Birds and bats catch insects in flight. Woodpeckers hammer into the bark of trees for grubs, other birds comb the leaves with their bills for small insects, and hawks swoop down on rodents and on other birds.

The kangaroo rat is a harmless little animal that lives in the deserts of the south western United States. It lives on dry thistle and cactus leaves, seeds, and small juicy tubers that grow abundantly in the desert 1 to 2 inches (2.5 to 5 centimetres) below the surface. It collects seeds in its cheek pouches and stores them in underground chambers. Gophers and chipmunks also collect food in their cheek pouches and store it in underground pantries for future use.

Carnivores, Herbivores, Insectivores

Animals that eat other animals are called carnivores. The shark is a fierce carnivore. It lives on smaller fish, such as mackerel. Many mammals are carnivores. They all have special kinds of teeth for tearing their food into chunks and chewing it. Most of them have claws for catching and holding their prey. Among the carnivores are cats, dogs, raccoons, weasels, bears, hyenas, and civet cats. Some fish subsist on plant and animal life known as plankton. The baleen whale is an enormous animal, growing up to 100 feet long. It feeds upon shrimp like creatures only about 1 inch in length. When it finds a school of shrimp, it opens its mouth and gulps in several barrels of water. Horny strainers that hang from the roof of its mouth catch the shrimp and drain out the water.

A large group of animals are plant eaters (herbivores). Many herbivores are prey of the carnivores. Insects are the dominant herbivores in most parts of the world, although they may be less conspicuous than plant-eating mammals and birds. Herbivorous mammals include horses, cattle, sheep, goats, rabbits, rodents, elephants, deer and antelope, and monkeys and apes.

A few mammals live on insects moles, shrews, and hedgehogs, bats, armadillos, aardvarks, and anteaters. Many bird species are insect eaters, as are certain kinds of insects, such as ladybugs.

How Animals Sense Their Surroundings

The ability of animals to sense and respond to their surroundings is one way in which they differ from plants. Higher animals have sense organs to perceive light, sound, touch, taste, and smell.

Eyes are very important to most mammals. Animals that hunt and feed by night have very large eyes. Cats’ eyes have pupils that can open wide in the dark and narrow down to slits in the sunlight. Insects have compound eyes, made up of tiny units that break up the image into many small pictures. They also have two or three simple eyes that probably detect motion. The eyesight of some fish is especially keen.

Fennec fox, name of several species of small, fox like animals characterized by large pointed ears.

Ears are perhaps as important as eyes to some species. The fennec is a fox like animal that lives in the Sahara and hunts by night. Its large ears help it detect its prey in the darkness of a hot, dry climate, where food may be very scarce. The cat is also a night prowler, and it too has large, erect ears. The hearing organs of the field cricket and katydid are located on their forelegs. The organ is a thin membrane that vibrates in response to sound waves.

Many animals have sense organs unlike those of the mammals. The antennae of the moths, butterflies, and other insects seem to correspond to the organs of taste, touch, smell, and hearing.

Barbel, a soft, slender feeler around mouth of certain fishes, such as catfish, cod, drum fish, goat fish, sturgeon.

The barbels of the catfish and the whiskers of the flying squirrel and the cat are organs of touch. They are very useful for animals that explore in the dark. The lateral line of the fish is a rod of nerve cells running the length of the body. It probably helps the fish feel movements in the surrounding water.

The delicate forked tongue of the snake tastes the air. With it the snake can locate food and other snakes. The rattlesnake has sensory pits on the head through which it can detect a nearby warm-blooded animal. Even the simplest one-celled animals respond to touch. If a flatworm is touched, it may jerk away or curl up into a ball. It moves away from strong light or from water that is too hot or too cold.

In the warm, muddy rivers of Western Africa there are fish that send out small electric impulses and surround themselves with an electric field. Whenever another fish or other object approaches, the fish is made aware of it by the changes in the charged field. Thus a built-in electric system takes the place of eyesight in the dark waters and keeps the fish informed of its surroundings. Bats emit high-pitched squeaks and use the reflected sound waves to avoid objects and locate prey while flying. Dolphins and whales send out ultrasonic signals and are able to detect objects by reflections of the sound.

Migration and Hibernation

When winter comes to northern or high-mountain regions, animals must find some way to keep warm. Many birds and some mammals seek a mild climate by moving south or to lower elevations. They are said to migrate. Other kinds of mammals (bears and woodchucks, for example) store up fat in their bodies in the fall by eating all they can. Then they curl up in a cave or some other protected place and sleep during the cold period that is, they hibernate.

Most insects die in the wintertime. They leave well-protected eggs which hatch in the spring. Fishes, frogs, and aquatic arthropods and other water-dwelling animals may hibernate in mud or move to deeper water and become inactive.

Living Together in Colonies

Social insects, those living in communities and having differentiated forms or castes, as queens, workers, drones.

Some animals live with others of their own kind. Ants, honeybees and bumblebees, and wasps are called social insects because they live together in highly organized societies.

Some birds live in large colonies. Penguins, anis, and eider ducks are examples. Weaver finches work together to build huge community dwellings.

South American monkeys travel through the jungles in family groups. They scatter while they are searching for food but stay within sight or hearing of one another. Toward evening they regroup and spend the night together. Baboons live in large bands. They cooperate in getting food and post sentries to watch for danger when the group stops.

Posted 2012/01/29 by Stelios in Education

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ANIMALS (Part 3 of 4)   Leave a comment

Intelligence

Most animal activities that appear to indicate intelligence are simply instinctive. The most intelligent animals are the apes and monkeys. Dogs and elephants have been trained to serve humans in many ways. Horses, seals, porpoises, lions, and tigers are often taught to perform in circuses and aquariums. Talking birds, such as parrots, parakeets, and mynahs, learn to imitate sounds, but they do not have the capacity to think or to understand what they are saying.

Relationship to Human

Humans require the presence of other animals in a variety of ways. The domestication of animals has been important to the development of civilization. By pollinating flowers, bees help in the cultivation of orchard fruits, alfalfa, clover, and many vegetables. The earthworm, by churning up the soil, improves the growth of plants.

Birds eat insect pests, weed seeds, and rodents. Certain bats eat so many mosquitoes and other insects that some communities erect shelters for them to encourage their help. Hyenas, vultures, and carrion beetles keep country regions clean by devouring dead animals.

Countless animal products are used by humans: pearls (from the oyster), shellac and lacquer (from the lac insect), glue, and fertilizers are only a few examples. Important drugs are produced from the blood and glands of animals. Serums and antivenins for snakebite are made from the blood of horses. Experiments performed on such animals as rats, mice, guinea pigs, and monkeys have been responsible for great advances in medical knowledge and the conquest of human disease.

Dangerous animals include the parasites in the human body and in domesticated animals that cause serious diseases. Fleas, lice, rats, and mosquitoes are also carriers of such serious conditions as malaria and encephalitis. Insect pests cause billions of dollars’ worth of damage every year.

THE BASIC FORMS OF ANIMAL LIFE AND HOW THEY DIFFER

More than a million different kinds of animals inhabit the Earth. No one knows exactly how many kinds there are, for many new ones are discovered and named every year.

Beginnings of Animal Life

The first organisms in the history of the Earth must have been one-celled bits of protoplasm floating in shallow seas and ponds. Here they remained for millions of years. They developed from one cell to many cells, becoming more and more complex. In time some animals moved into fresh water. Others began to live on land. In these surroundings they changed still more, until today there is a bewildering variety of forms.

The creatures that developed a backbone and an internal skeleton are called vertebrates. They include all the familiar animals the mammals, reptiles, birds, fish, and amphibians. Animals without backbones are called invertebrates. They include insects, sponges, corals, jellyfish, clams, lobsters, and starfish.

The vertebrates make up only about 5 percent of all animal species. Invertebrates compose the remaining 95 percent. There are some 4,000 species of mammals. Insects number about one million species.

How Animals Are Classified

Phylum (from Greek, meaning tribe), a major division in biological classification.

To study the many forms of animal life in a systematic way, scientists have divided the animal kingdom into groups. These groups are based upon the structure of the animal’s body. The largest divisions are phyla (singular, phylum). The word phylum means “race” or “tribe.” The phyla are groups of animals with fundamentally different body plans.

Order, in biological classification, a group of related families.

Genus (plural, genera), a group of related species of plants or animals.

Each phylum is divided into classes, the classes into orders, and the orders into families. Families are subdivided into genera (singular, genus), and each genus is divided into species. All members of the same species are closely related. They are capable of interbreeding and producing fertile offspring. Animals of different species do not normally interbreed. Every animal has a scientific name, or binomial (having two names), consisting of the genus and species.

How Classification Shows Relationships

Classification shows relationships between animals in an increasingly specific order, from remotely related members of the same phylum to closely related species within a genus. House cats (Felis catus) and bobcats (Felis rufus) belong to the same genus (Felis) and family (Felidae) but to different species.

Dogs and cats do not appear to be related. Both, however, have backbones and are meat-eating mammals. Hence they belong to phylum Chordata (having a spinal cord), class Mammalia (mammals), and order Carnivora (flesh eaters); because of differences between them, however, they belong to separate families (dog, Canidae; cat, Felidae).

Whales and sharks both appear to be kinds of fish. Both are strong, streamlined swimmers of the sea. However, the whale is a mammal. It has lungs and is warm-blooded, gives birth to live young, and nurses its offspring with milk. Whales therefore belong to the class Mammalia. The shark, on the other hand, is a primitive kind of fish with a skeleton of cartilage instead of bone. Sharks, whales, and true fishes all have a backbone. Thus, they are placed in the same phylum (Chordata) and subphylum (Vertebrata). Sharks and fishes, however, are also in different classes, the sharks being in the Chondrichthyes and the true fishes in the Osteichthyes.

Classification also suggests which kinds of animals may have descended from other types. All multi-celled animals, for example, are supposed to be descendants of one-celled animals. This does not mean descent from one living kind of animal to another, however. All living animals are believed to have descended from common ancestors that were less specialized than they. These relationships may be shown on a treelike diagram called a phylogenetic tree. The word phylogenetic comes from two Greek words meaning “race history.”

Animals Without Backbones Invertebrates

The simplest animal-like organisms consist of a single cell a bit of protoplasm containing one nucleus. These organisms are called protozoans, which means “first animals” in Greek. These creatures are sometimes considered animals, but most classification schemes place them in a separate kingdom known as the Protista. Protozoans are very adaptable. They live in salt and fresh water, in moist earth, and as parasites in other animals.

Aside from the protozoans, all members of the kingdom Animalia have many cells and are referred to as metazoans. The simplest multi-celled animals make up the phylum Porifera (“pore bearers”). The most familiar kinds are the sponges. They are called pore bearers because they are covered with millions of tiny holes. Water flows through the holes, and from the water the sponges take in oxygen and the tiny water borne organisms that constitute their food and filter out wastes. Sponges have no mouth or digestive cavity, no nervous system, and no circulatory system. Several types of cells are present, but each generally functions as a unit without forming tissues, as in more complex metazoans. (Tissues are groups of similar cells bound together to perform a common function.)

Pouch like Animals

Coelenterata, phylum of animals including coral, hydra, jellyfish, and sea anemone.

The next, less primitive structural pattern in invertebrates is a hollow gut. The representative phylum is Coelenterata, a term stemming from the Greek words koilos (hollow) and enteron (intestine). Among the coelenterates are the corals, hydras, jellyfishes, and sea anemones. The body is composed of two tissue layers. The inner layer, or endoderm, lines the central digestive cavity. The outer layer, or ectoderm, protects the animal externally.

The coelenterates have a mouth like opening the only opening into the gut that takes in food and ejects waste material. Food-gathering organs such as tentacles and protective structures such as stinging cells surround the mouth. There is a primitive nervous system. (Coelenterates are also sometimes called cnidarians.)

Bilateral Animals with Heads

All the animals described above are headless creatures. They are either irregular masses or animals with shapes like a globe, a cylinder, a bowl, or a wheel. The latter are said to have spherical or radial symmetry; that is, they have similar body parts regularly arranged around a centre or a central axis, respectively. Some drift around in ocean currents, unable to swim efficiently in any particular direction. Some of them in their adult stages the corals and sponges, for example fasten themselves to fixed objects and do not move at all.

A flatworm called Dugesia, or planaria, is interesting because it shows two very important improvements in body structure. It belongs to the phylum Platyhelminthes (flatworms). It is the most primitive animal that has a definite head bearing sense organs. The mouth is on the underside of the triangular head. The body is differentiated into a front end and a rear end, a top and a bottom. It has bilateral symmetry: each half of the body is a mirror image of the other half. Most of the higher animals, including humans, are built on this pattern of body structure.

Platyhelminths are also the most primitive, living animals to have three cell layers. Between the ectoderm and the endoderm, which first appeared in the jellyfish and their relatives, is a middle layer: the mesoderm. Two-layered animals are small and fragile. The third layer gives solidity to the body and permits the animal to grow to a large size. Muscles and other complex organs develop from this layer.

Segmented Worms

Segmented worms have a more developed digestive system than Dugesia, which takes in food and ejects waste material through the same opening in the head. Segmented worms have a digestive tube with two openings a mouth and an anus through which wastes are expelled. The phylum Annelida (meaning ringed, or segmented) has a digestive system built on the same plan as the vertebrates. Earthworms and leeches are familiar annelids.

The Soft-Bodied Animals

The phylum Mollusca (from the Latin word for “soft”) includes the clam, oyster, chiton, snail, octopus, and squid. Molluscs have soft, fleshy bodies not divided into segments. The main part of the body is enclosed in a fold of tissue called the mantle. They have bilateral symmetry. Many of them are covered by a shell. They have a solid, protective structure outside the body, called an exoskeleton.

Posted 2012/01/29 by Stelios in Education

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ANIMALS (Part 4 of 4)   Leave a comment

The Largest Group of Animals

The phylum Arthropoda (“jointed foot”) has the largest number of species. In fact, about 90 percent of the million or more species living on the Earth today are arthropods. The insects total more than 800,000 species. Other arthropods include the centipedes and millipedes; the arachnids (spiders, scorpions, ticks, mites); and the crustaceans (barnacles, crabs, crayfish, lobsters, shrimp, water fleas). Obviously, the arthropod body plan has been highly successful. The members of this great phylum live on land, in fresh water, and in salt water. They can walk, fly, burrow, and swim. This is the only invertebrate group with jointed appendages (legs, feet, and antennae).

Arthropod, animal of the phylum Arthropoda comprising invertebrates with external skeleton, segmented body, and jointed appendages.

Arthropods, like molluscs, wear a supporting framework, or exoskeleton, on the outside of the body. Much more highly developed than the heavy, clumsy shell of the clams and snails, it is made of a substance called chitin. Rigid, waterproof plates of chitin are joined by thin, flexible membranes of chitin so that the animal can move freely and quickly. The muscles are attached to the inner surface of the armour Many important structures are connected to the outer surface. For example, the wings, legs, jaws, and antennae of the insects are all made of chitin and are attached to the outer skeleton. The body is divided into sections, or segments.

Spiny-Skinned Animals

One phylum with the characteristics of several others is the Echinodermata (“spiny-skinned”). All members of the group, which includes starfishes, sea urchins, holothurians (sea cucumbers), and crinoids (sea lilies), live in salt water some in the shallow shoreline waters, others in the ocean depths. The young, called larvae, have bilateral symmetry, but the adults have radial symmetry, like the coelenterates. These are the most primitive creatures having an endoskeleton, or skeleton that is embedded in the flesh. It consists of a mesh work of plates that are made of calcium. The plates are joined by connective tissue and muscles. Spines project from these plates.

Animals with Backbones

At the top of the animal kingdom is the phylum Chordata. This phylum consists of two groups of primitive chordates the tunicates and the cephalochordates and the main group of the vertebrates.

The major subdivisions, or classes, of the vertebrates are the fish, amphibians, reptiles, birds, and mammals. Members of this phylum possess the following structures at some period of their life, either as embryos or as adults:

Notochord. This is an internal supporting rod extending the length of the body. It is found in the embryos of all chordates, including human beings. Only the most primitive forms, such as the amphioxus, or lancelet, the lamprey, and the hag fish, retain it as adults. Remnants of the notochord are also present in sharks. In the higher chordates, such as amphibians, reptiles, birds, and mammals, the notochord is replaced during development of the embryo by a bony column of vertebrae, which gives the column and the animal flexibility.

Nerve tube. This lies in the mid line of the body on the top (dorsal side) of the notochord. In the annelid worms and the arthropods the main nerve is solid and lies on the underside (ventral side). In most chordates the forward end of the nerve tube forms a brain; the remainder is the spinal cord.

Pharyngeal gill slits or pouches. The lower chordates, such as the fish, breathe through openings in the side of the neck in the region of the pharynx. The embryos of the higher chordates have these slits, but they disappear in the adult.

Primitive Chordates

Amphioxus (or lancelet), a fish-shaped sea animal; about 2 in. (5 cm) long; pinkish white; several species known; classed in the phylum Chordata, subphylum Leptocardia.

The amphioxus is characteristic of the most primitive chordates. This animal is a laterally compressed, semitransparent sea dweller about 4 inches (10 centimetres) long. Scientists believe that it may be one of the ancestors of the vertebrates. It has a notochord and a tubular nerve cord along the back. It has no well-developed brain, however, and only traces of eyes and ears. Pigment spots along the body are sensitive to light. The pharyngeal gill slits strain food from the water. The tunicates, or sea squirts, and acorn worms are other primitive chordates.

Lampreys and hag fishes are the most primitive of the true vertebrates. They have a notochord. The skeleton is composed of cartilage. They lack jaws and paired limbs.

Mammals

Mammals differ from other vertebrates in that they have bodies that are covered with hair at some period of their lives. They are warm-blooded, meaning that their body temperature is largely unaffected by the temperature of the air or water in which they live. The females have milk glands to feed their young. Whales, as noted earlier in this article, dolphins, and porpoises are the most unusual-looking mammals because they resemble fishes. The most primitive mammals are the egg-laying platypus and the echidna, or spiny anteater. The marsupials, which incubate their unborn offspring in a pouch for a time, are also considered to be somewhat primitive. The remaining mammals transmit nourishment to their unborn young through a placenta and give birth to fully developed offspring.

Assisted by J. Whitfield Gibbons, Senior Research Ecologist and Professor of Zoology, Savannah River Ecology Laboratory, University of Georgia.

BIBLIOGRAPHY FOR ANIMAL

Books for Children

Alday, Gretchen. Devoted Friends: Amazing True Stories About Animals Who Cared (Betterway, 1990).

Aylesworth, T.G. Animal Superstitions (McGraw, 1981).

Gabb, Michael. Creatures Great and Small (Lerner, 1980).

Hirschi, Ron. Who Lives In the Forest? (Dodd, 1987).

Hutchins, R.E. Nature Invented It First (Dodd, 1980).

Lauber, Patricia. What’s Hatching Out of That Egg? (Crown, 1979).

Lopshire, Robert. The Biggest, Smallest, Fastest, Tallest Things You’ve Ever Heard Of (Houghton, 1991).

Lurie, Alison. Fabulous Beasts (Farrar, 1981).

McCauley, J.R. Animals and Their Hiding Places (National Geographic, 1986).

McGrath, Susan. Saving Our Animal Friends (National Geographic, 1986).

Patent, D.H. Sizes and Shapes in Nature What They Mean (Holiday House, 1979).

Pope, Joyce. Do Animals Dream? (Viking, 1986).

Prince, J.H. How Animals Move (Elsevier/Nelson, 1981).

Pringle, L.P. Feral: Tame Animals Gone Wild (Macmillan, 1983).

Schulz, C.M. Charlie Brown’s Super Book of Questions and Answers About All Kinds of Animals (Random, 1976).

Sunden, Ulla, ed. Remarkable Animals (Guinness Books, 1987).

Sussman, Susan and James, Robert. Lies (People Believe) About Animals (Whitman, 1987).

Windsor, Merrill. Baby Farm Animals (National Geographic, 1984).

Books for Young Adults

Adamson, Joy. Born Free (Pantheon, 1987).

Adamson, Joy. Living Free (Harcourt, 1961).

Argent, Kerry. Animal Capers (Doubleday, 1990).

Baker, M.L. Whales, Dolphins, and Porpoises of the World (Doubleday, 1987).

Burton, Maurice. Cold-Blooded Animals (Facts on File, 1986).

Burton, Maurice. Warm-Blooded Animals (Facts on File, 1987).

Burton, Maurice and Burton, Jane. The Colorful World of Animals (Longmeadow, 1975).

Gibbons, Whit. Their Blood Runs Cold: Adventures with Reptiles and Amphibians (Univ. of Ala. Press, 1983).

Herriot, James. All Creatures Great and Small (St. Martin’s, 1972).

Herriot, James. All Things Bright and Beautiful (St. Martin’s, 1974).

Herriot, James and others. Animal Stories, Tame and Wild (Sterling, 1985).

Kohl, Judith and Kohl, Herbert. Pack, Band, and Colony: The World of Social Animals (Farrar, 1983).

Milne, Lorus and Milne, Margery. A Time to be Born (Sierra Club, 1982).

National Geographic Book Service. Wild Animals of North America, rev. ed. (National Geographic, 1987).

Nowak, R.M. and Paradiso, J.L. Walker’s Mammals of the World (Johns Hopkins Univ. Press, 1983).

Posted 2012/01/29 by Stelios in Education

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BEETLES (Part 1 of 2)   Leave a comment

 

Giraffe beetle. Also Giraffe weevil.

DEFINITION:1 any of a large order (Coleoptera) of insects, including weevils, with biting mouth parts and hard front wings (elytra ) that cover the membranous hind wings when the hind wings are folded 2 any insect resembling a beetle.

There are more species of beetles than of any other kind of insect. They constitute the largest order of insects Coleoptera which includes almost one third of a million recognized species. About 20 percent of all known species of animals in the world are beetles.

Beetles are found throughout all continents except Antarctica. Although most species are terrestrial, many such as the whirligig, water scavenger, and true water beetles have become adapted to aquatic environments. Some beetles are only about 0.01 inch (0.025 centimetre) long, whereas tropical rhinoceros beetles and Goliath beetles may reach lengths of 4 to 6 inches (10 to 15 centimetres).

Beetles display a remarkable array of colours, forms, and habits. Some are plain black or have brownish patterns that help to camouflage the insects against certain types of wood or soil. Some beetles are brilliant orange, red, or yellow; others are iridescent green or blue or have a metallic sheen. The antennae of some beetles are large and ornate. Some stag beetles have enlarged, hooked mandibles, or lower jaws, that are almost as long as the beetle itself. Male rhinoceros beetles have huge horns projecting over their heads. The shapes of beetles’ bodies vary from round to elongate. Some are flattened; others are domed or cylindrical.

Some beetles are of great significance to humans. Members of the family of beetles known as weevils, or snout beetles, are notorious agricultural pests. They have specialized, elongated heads and down-curved snouts with mouth parts at the end. Some beetles feed on plant materials such as wood, paper, and fabrics. The larvae of some dermestid beetles are destructive pests of clothing and carpets and even of plant and animal specimens in museums.

Many beetles are valuable because they prey on destructive insect pests. Ladybugs, for example, destroy untold numbers of aphids each year and so protect a wide variety of flowers and vegetables. Many other beetles play more subtle but equally important roles in various ecosystems. Dung beetles, or tumble bugs, eat vast quantities of dung in livestock areas. Carrion beetles are scavengers whose larvae feed on dead animals. Many beetles pollinate flowers.

Physical Characteristics

Mandible, from Latin mandere, to chew; term applied to: (1) chewing jaws of insects and other arthropods; (2) the lower jawbone of mammals; (3) the upper or lower part of a bird’s beak.

Like other insects, beetles have three major body segments: the head, with a single pair of antennae and a pair of compound eyes; the thorax, which bears two pairs of wings and three pairs of legs; and the abdomen, where the reproductive organs are housed. Beetles have chewing jaws called mandibles and paired structures known as maxillary and labial palpi (singular, palpus) that are used for feeding or handling food. The bodies of beetles and other insects are covered by a usually hard layer known as the cuticle that supports the internal organs and protects the body. The cuticle is hard because it contains a substance called chitin. Each defined, plate like area of the cuticle is called a sclerite.

A distinctive feature of beetles is their front pair of wings, which are thick, hard, and opaque, without the veins characteristic of most other insect wings. These fore wings, called elytra (singular, elytron), serve as protective wing covers for a second pair of functional wings underneath. The hind wings are membranous and translucent. These are ordinarily used for flying, while the heavy elytra are held out of the way. When the beetle is at rest, the elytra fold over the back and form a straight line down the centre where they meet. Some beetles have shortened wings, and a few species are entirely wingless.

Life Cycle and Behaviour

Like other insects, beetles reproduce sexually by means of internal fertilization. The ovaries of the female and testes of the male are enclosed within the abdomen. In some species, such as the stag beetles, males engage in combat with one another for the right to mate with the females. After mating, the females lay the fertilized eggs in a location suitable for development of the larvae.

Beetles undergo a complete metamorphosis: they develop from egg into active larva into inactive pupa and finally into an adult. The larva, or grub, does not resemble the adult in structure. The pupal stage though soft, pale, and immobile does have the body form of an adult. The life spans of beetles range from a few months in some species to more than four years in others.

Feeding habits. Most beetles feed on living or dead plant materials, but some are scavengers of dead animal matter and some prey on other insects. A few are parasites.

The adults and larvae of a number of beetle species feed on various plant roots, stems, fruits, seeds, and foliage. Some beetles feed only on certain plant species and plant parts, whereas others are less particular in their choice of foods. The adults and larvae of many beetles feed on decaying wood and help break down dead trees and other vegetation in forest habitats.

Some beetles, such as tiger beetles, are voracious predators. Adult tiger beetles search for prey that they can subdue with their powerful mandibles. The larvae are sedentary; they live in small tunnels where they wait to capture passing insects. Water scavenger beetles are predators as larvae but are plant eaters as adults. Some species of beetles have highly selective feeding habits: they may eat only mites, ant larvae, aphids, or zoo plankton

Defences Although most beetles are protected by their heavy armour, some species have developed additional methods of defence Blister beetles secrete an oily, blister-causing substance that deters predators. Beetles may also discourage or avoid predators by making a startling noise (see below, “Light and sound production”), secreting or ejecting an obnoxious fluid, biting, hiding (using their natural colouring as camouflage), or simply fleeing on foot or on wing.

Luminescence, emission of light resulting from causes other than high temperature.

Light and sound production. Many beetles are capable of producing light and sound, primarily for the purposes of attracting a mate or for frightening enemies. The familiar fireflies, or lightning bugs, are beetles that have special light organs on the underside of their abdomens. These beetles usually the males flash their lights rhythmically as a signal that they are ready to mate, and the females return the signal. The kind of signal system used by the two fireflies allows males and females of the same species to recognize and locate one another. Some tropical click beetles have large, luminescent eye spots on the back of the thorax that presumably are also used in courtship.

Many species of beetles make sounds by rubbing together hard parts of their bodies a practice called stridulation. The vibration created by the friction of these parts produces a shrill creaking noise. Beetles may stridulate by rubbing the two elytra together, by rubbing a hind leg against an elytron, or by rubbing the head against the front of the thorax. In some species, even the immature grubs can produce sounds. Although stridulation is often used by adult beetles as a mating signal, its purposes in other instances by juveniles, for example are not fully understood.

A wood-boring beetle known as the death-watch beetle strikes its head against the sides of its burrow as a mating signal. The name death-watch is derived from the superstition that the sound was an omen of death. One explanation is that the ticking sound of a death-watch beetle that had made its burrow in an old piece of furniture was most often heard late at night by someone sitting at a sickbed.

When threatened by a predator, bombardier beetles squirt, with a loud popping sound, an unpleasant-smelling liquid from the rear of their abdomens. The noise and the ejection act together to startle and repel the predator and give the beetle time to make its escape. When click beetles fall on their backs, they right themselves by snapping their bodies in such a way that they are tossed into the air with a loud clicking sound that can startle a predator.

Kinds of Beetles

There are many families of beetles about 135, according to some experts. The beetles discussed below represent a sampling of some of the most commonly known as well as some of the most unusual beetle families in the order Coleoptera.

Tiger beetles and ground beetles are the most common beetles in North America. The fierce, long-legged tiger beetles are fast-running, fast-flying, often brightly coloured beetles that capture and eat other insects. Species of tiger beetles occur throughout the world but are especially abundant in the tropics.

Ground beetle, one of a group of the order Coleoptera, family Carabidae; especially the fiery searcher (Calosoma scrutator), one of the largest beetles; if held carelessly will discharge quantities of “fiery” juice.

Ground beetles are also abundant in most parts of the world. Many species are black and shiny; some are iridescent. Like the tiger beetles, ground beetles have long legs. Some have enlarged, pinching mandibles that are used to capture prey. Many are nocturnal.

True water beetles (also known as diving beetles or predaceous diving beetles) are oval-shaped insects that can swim, dive, and fly. They are found in most freshwater habitats worldwide but are most common in northern temperate regions. The hind pair of legs of the true water beetle are long, flattened, and fringed to provide a greater surface area that helps the insect float. The beetle breathes through spiracles openings on the abdomen just under the tips of the elytra. Before diving, the beetle collects an air bubble beneath its elytra and then breathes from the bubble while it is underwater. It is carnivorous, preying on insects and other aquatic organisms, including fish larger than itself. The larvae of the true water beetles are sometimes called water tigers because of their voracious appetites. True water beetles often fly from one aquatic habitat to another and may be seen around outdoor lights at night.

Whirligig beetles, like the true water beetles, are oval-shaped aquatic predators that can swim, dive, and fly. They are known for their gregarious habits they are usually seen in groups, spinning and whirling around on the surfaces of quiet ponds or lakes. They have distinctive, divided eyes a top pair for seeing above the water’s surface and a bottom pair for seeing below.

Posted 2012/01/25 by Stelios in Education

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BEETLES (Part 2 of 2)   Leave a comment

Water scavenger beetles include more than 1,000 species of primarily tropical aquatic beetles, with approximately 200 species native to North America. Like the true water beetles, water scavenger beetles must find a way of supplying themselves with oxygen while they forage underwater. At the water’s surface, the beetles project their antennae out of the water to capture a bubble of air. Then they place the bubble beneath their bodies to breathe from it as they swim. This bubble makes water scavenger beetles look as though they have a silvery film on their undersides.

Carrion beetles and burying beetles are widely distributed and eat primarily dead animal matter. Many carrion beetles are relatively large and brightly coloured Burying beetles are so named because they dig beneath small dead animals such as rodents, birds, and reptiles until the animal is completely buried beneath the soil. Then the female digs her way down to the carcass and deposits her eggs. Upon hatching, the larvae feed on the body of the dead animal.

Rove beetles have short elytra that do not cover the abdomen. When they are being pursued, rove beetles run with the tip of their abdomens curled over their backs, giving their abdomens the appearance of stingers. One species expels a fluid from the tip of its abdomen that repels attacking ants.

Luminescence, emission of light resulting from causes other than high temperature.

Fireflies are soft-bodied beetles, most of which produce light in special organs located in the undersides of their abdomens. The light is produced by a chemical reaction between oxygen in the air and two chemicals in the firefly’s body. The females of most species have short wings or are wingless. The wingless females and most firefly larvae are often called glow worms Some species in the firefly family do not produce light.

Stag beetles are best known for their enormous, distinctive mandibles. These are most pronounced in the males. Stag beetles are often found in and around rotting logs, on which the larvae feed. Adults are often attracted to outdoor lights.

Scarab beetles include a wide variety of species about 20,000 worldwide. More than 1,300 species occur in North America. Most scarab beetles are stout and robust, but their size varies greatly from one species to another. Some small species are about 0.08 inch (0.2 centimetre) in length, whereas some of the tropical species are the largest beetles in the world up to 6 inches (15 centimetres) in length. Some members of the scarab-beetle family are scavengers: both the larvae and the adults feed on dung and carrion. Others are plant eaters: the larvae eat roots or wood and the adults eat leaves and flowers. Many members of the latter group are agricultural pests. June bugs and May beetles are scarabs.

Click beetles are small to medium-sized beetles with elongated, flattened bodies that have bluntly rounded ends. The largest species reach lengths of about 2 inches (5 centimetres). The larvae of click beetles, called wire worms, cause extensive crop damage in some areas because they feed on underground roots, seeds, and stems.

Metallic wood-boring beetles resemble click beetles in general shape but can be distinguished by their bright metallic colours Some species damage orchards and forests.

Dermestid beetles are mostly small, scavenging beetles. In the household they are particularly harmful to stored foods, leather, furs, and wool products. Although the adults and larvae are scavengers, most of the damage is done by larvae.

Ladybugs, with their roundish, brightly coloured bodies, are the favourite insects of many people. The adults and larvae are often predators of other invertebrates that are agricultural or garden pests, and many fruit growers consider ladybugs to be among the most beneficial of insects.

Darkling beetle, any beetle of the family Tenebrionidae, which includes meal worms, flour beetles, and other species occurring under stones, in dead wood, fungi, and dry vegetable products; most are black or brown.

Darkling beetles include about 15,000 species worldwide. Of the more than 1,400 species in the United States, most are found in the arid South west Most darkling beetles are solid dull black in colour Meal worms are actually the larvae of darkling beetles. Although they are major pests of grain products, meal worms are also commonly raised as food for insect-eating animals such as lizards, frogs, and birds.

Cantharidin, blistering substance obtained from Spanish-fly beetle and other insects of same family.

Blister beetles are elongate, relatively soft-bodied beetles. The adults of most species feed on plants. Blister beetles secrete an irritant called cantharidin. The substance has been used to produce a drug that causes a blistering reaction on the skin most often as a topical skin irritant to remove warts. The substance was first extracted from a bright green blister beetle of southern Europe known as Spanish fly. The drug, also called Spanish fly, was once considered an aphrodisiac, but it can be toxic if taken internally.

Long-horned, wood-boring beetles are often medium-sized to large 0.8 to 2.4 inches (2 to 6.1 centimetres) in length with extremely long antennae. The larvae of these beetles are usually wood-borers that feed on a variety of trees and can cause considerable damage. More than 20,000 species have been described worldwide, and at least 1,200 of these are native to North America. Some are brightly coloured and metallic in appearance.

Leaf beetles are abundant and widely distributed. They are relatively small, and many are brightly coloured and resemble ladybugs. The adults and larvae feed on foliage and also on other plant parts.

Engraver beetle, any of numerous beetles of family Scolytidae; most live under bark of trees and engrave the wood by burrowing.

Bark beetles are considered the most destructive insects of temperate-zone forests. Both the adults and the larvae live beneath the bark of trees. The damage they inflict on the tree depends on the species. Engraver beetles, for example, feed on the inside of the bark and on the surface of the trunk. Other bark beetles bore directly into the trunk and feed on the wood. Ambrosia beetles bore into the tree’s trunk and feed on fungi that live there. Members of the bark-beetle family are dark-coloured. Their antennae are elbowed and have an enlarged, club like end.

Weevils, or snout beetles, constitute an abundant and diverse beetle family with more than 40 subfamilies and 40,000 recognized species. Their most characteristic feature is the beak or snout. It is well-developed, curves downward, and in some species may be twice as long as the body. The snout is used not only for penetration and feeding but also for boring holes in which to lay eggs. The weevils’ antennae are elbowed and club-shaped at the end. Many weevils have no wings; others are excellent fliers. Most are less than 0.25 inch (6 millimetres) in length and are plainly coloured and marked, yet the largest exceed 3 inches (80 millimetres) in length and may be brightly coloured This family includes some extremely destructive pests, such as the grain weevil and the rice weevil.

Taxonomy

Taxonomists divide the Coleoptera into two or more suborders, depending on the classification scheme they prefer. The two suborders common to most schemes are Adephaga and Polyphaga. The suborder Adephaga consists of several families of beetles that are mostly predaceous, including the tiger beetles and ground beetles, the true water beetles, and the whirligig beetles. The suborder Polyphaga contains the majority of beetles.

Tiger beetles and ground beetles belong to the family Carabidae, which contains the largest number of beetle species in North America. (Some taxonomists place tiger beetles in a separate family, Cicindelidae.) Bombardier beetles are also members of the Carabidae family. The true water beetles are in the family Dytiscidae, whirligig beetles are in Gyrinidae, and water scavenger beetles are in Hydrophilidae. Carrion beetles and burying beetles belong to the family Silphidae. Rove beetles are in the family Staphylinidae and have almost as many species in North America as does the family Carabidae. Fireflies and glow worms belong to the family Lampyridae. Stag beetles are in the family Lucanidae. Scarab beetles belong to the family Scarabaeidae, which includes the rhinoceros beetles, Goliath beetles, and dung beetles. Click beetles are in the family Elateridae. Metallic wood-boring beetles are placed in the family Buprestidae. Dermestid beetles belong to the family Dermestidae, and ladybugs are in the family Coccinellidae. Darkling beetles are in the family Tenebrionidae. Blister beetles belong to the family Meloidae. The long-horned wood-boring beetles are classified in the family Cerambycidae, and leaf beetles are placed in the family Chrysomelidae. Bark beetles belong to the family Scolytidae. Weevils belong to the largest family of beetles in the beetle order the family Curculionidae. Bess-bugs belong to the family Passalidae. The death watch beetle is in the family Anobiidae.

Assisted by J. Whitfield Gibbons, Senior Research Ecologist and Professor of Zoology, Savannah River Ecology Laboratory, University of Georgia.

Posted 2012/01/25 by Stelios in Education

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PROTECTIVE COLOURATION   Leave a comment

 

Monarch butterfly

DEFINITION: (or colouring) natural colouration of certain organisms allowing them to blend in with their normal environment and escape detection by enemies.

As animals evolved, most of them developed body colours and markings that improved their chances of surviving. This adaptive mechanism, known as protective colouration, may serve any number of functions. Colouring can help protect an animal by making it hard to see. For an animal that spends much of its life trying to avoid dangerous enemies, this is the most useful function. Thus protective colouration is often found among the most helpless creatures those who have little or no other means of defence A white snow hare, for example, blends into its white surroundings and so becomes less visible to predators.

Conversely, colour can help an organism by making it more conspicuous the bright colours of a poisonous snake may warn off intruders, for example. In general, the purpose of protective colouration is to decrease an organism’s visibility or to alter its appearance to other organisms. Sometimes several forms of protective colouration are superimposed on one animal.

Types of Protective Colouration

There are a variety of protective colouration schemes. Each works in a slightly different manner.

Cryptic colouration helps disguise an animal so that it is less visible to predators or prey. One of the most common types of cryptic colouration is background matching, which may take various forms. Many helpless animals have developed colours and markings that match their surroundings in order to hide from predators. Fish eggs and microscopic zoo plankton, for example, are transparent and nearly invisible as they drift in the upper layers of oceans and freshwater lakes. A fawn’s spotted coat camouflages the animal against the speckled forest floor. Some animals attempt to camouflage themselves physically. The decorator crab, for example, cements bits of algae, seaweed, and other ocean debris onto its shell so that it resembles the ocean floor.

Grasshoppers and other insects that live among green plants are often green, and insects that live in the soil, such as ants, are often earth-coloured. The pepper moth has coloured patches that camouflage it against the tree on which it lives. The Sargasso sea dragon lives amid masses of floating algae. The fish is not only coloured to match the plants, but its fins and scales are even shaped like algae. The oriental leaf butterfly, which lives on leaf-littered forest floors, is so intricately and completely camouflaged that its markings include leaf veins and a stem.

Sometimes it is the predator that is camouflaged. Certain predatory fish, for example, blend in with harmless schooling fish and then prey on members of the school. Some species of groupers are camouflaged against the ocean floor as they lie motionless, waiting for prey to swim by.

Certain animals can change their colour in response to different environments or situations. Certain lizards are well known for their ability to match their colour to their surroundings. Varying hares change colours with the season: through the winter their fur is white, and as the snow disappears, their fur turns brown. Thus they remain camouflaged throughout the year.

Another form of cryptic colouration is called disruptive colouration, a scheme in which spots, stripes, or other colour patterns visually break up an animal’s outline. Such patterns may mask the animal’s true shape or make it difficult for a predator to visually resolve it from a colourful or similarly disruptive background. Predators, such as the cheetah, tiger, and leopard, may use their disruptive colouration to avoid being seen. The spots or stripes on their fur allow them to get close to their prey before being observed, improving their chances of getting food. Many fishes and certain birds exhibit disruptive colouration, as do some snakes. The boa constrictor, a tree dweller that grows to several feet in length, is marked with a complex pattern of spots and stripes so complete that a stripe even extends across its eyes. Some patterns of disruptive colouration operate on the same principle to conceal movement. Snakes that are concentrically banded, for example, are difficult to detect when they move between long blades of grass.

A third form of cryptic colouration is counter shading, designed to mask an organism’s three-dimensional form. Many animals, particularly vertebrates, are counter shaded, or shaded lighter on their lower surfaces and darker on their upper surfaces. This colouration counteracts the effects of overhead light, which accentuates an animal’s three-dimensional form by lightening the animal’s upper body and casting its lower body into shadow.

Counter shading gives the body a more uniform darkness and less depth relief so that the animal is less conspicuous.

Many marine animals are counter shaded so that they will not appear as silhouettes when seen from below. A silhouetted organism would be conspicuous and thus attract predators. When viewed from above, counter shaded marine animals blend into the darkness of the sea bottom; when viewed from below, their light lower bodies match the appearance of the water’s surface.

Alluring colouration Some animals are coloured so that a predator’s attention is drawn to a non-vital part of the animal’s body. The lizard known as the blue-tailed skink has a bright blue tail that the animal can shed at will with no harm to itself. Potential predators are attracted to the tail; if they attack the tail, the skink sheds it and darts away unharmed.

Monarch butterfly, insect (Danaus plexippus) of the order Lepidoptera, family Danaidae; breeds on milkweeds.

Warning colouration is intended not to camouflage an organism but to make it more noticeable. Such colouration is found among animals that have natural defences that they use to deter or fend off predators. These defences can take many forms. An animal may simply cause a disagreeable smell (such as a skunk’s odour), or it may actually cause pain (as from bee’s sting) or even death (as from snake’s venom). Many of these animals are brightly coloured, presumably as a warning to potential aggressors. The monarch butterfly, for example which bears a conspicuous pattern of bright orange and black has such a disagreeable taste that a bird will often regurgitate after eating it. Behavioural biologists believe that predatory animals learn to associate such brightly coloured animals with unpleasant or painful experiences and therefore are likely to pass them up as potential prey in favour of a more drab animal. Common warning colours are red, black, and yellow.

Dewlap, in reptile anatomy, a hanging fold of skin under the neck.

Some organisms can change their colour from drab to bright when threatened. The octopus, for example, turns white when agitated and red when it is suddenly frightened. Certain chameleons, usually camouflaged, display a brightly coloured throat sac, or dewlap, as a warning signal to invaders. Furthermore, when a male chameleon enters another’s territory, the dewlap display of the territory’s “owner” serves as a warning to keep out.

Fin, in zoology, external membrane used for propulsion in water.

Other forms of protective colouration Some animals are coloured in such a way that they draw attention to themselves only when they are in motion. Certain birds have light-coloured feathers that are visible only during flight. When the bird comes to rest, these feathers are tucked under darker feathers, so that the bird is once again inconspicuous. Similarly, many fishes have colourful dorsal fins that are extended while the fish is swimming then folded down when the fish is at rest.

In both cases, the animal can use its colouration to perform a sort of disappearing act. It can draw a predator away from a certain area, perhaps a nest of vulnerable offspring, by catching the predator’s attention and moving to another location. If the predator pursues the decoy, the bird or fish can disappear by coming to rest.

Some organisms imitate the protective colouration of others. This phenomenon is known as mimicry. A harmless animal may display the same warning colouration as a dangerous or inedible one in order to deceive predators into reacting as though the benign animal had the same defences as its model. In other cases, several noxious species will share a similar warning colouration so that potential predators will generalize and avoid all species with such colouring

Evolution of Protective Colouration

The intricate schemes of protective colouration are the results of long-term evolution. Through aeons of adaptive changes, certain organisms have acquired patterns of colouration that have helped them survive and reproduce.

Effective forms of protective colouration have been passed on to following generations. The processes of mutation, natural selection, and reproduction have combined to produce many organisms with colourations that are fine-tuned to their individual environments and their individual protective needs.

Assisted by Elliot Mitchell, science teacher, Latin School of Chicago.