ANIMALS

TWO BIG GROUPS OF ANIMALS

Animals are classified into two big groups based on similarities in their structure.

The group of animals without backbones dominates the world. These are called invertebrates. They make up 90% of all animal species.

A small portion of the millions of animals comprise the vertebrate group, those with backbones.

VERTEBRATES

They are further divided into five main classes. These are:

1. Fishes 2. Amphibians 3. Reptiles 4. Birds 5. Mammals

INVERTEBRATES

This big group of invertebrates is composed of:

Sponges Coelenterates Flatworms Roundworms Segmented worms Echinoderms Mollusks and the Arthropods.

VERTEBRATES ALSO HAVE DIFFERENCES.

The fishes, amphibians, and reptiles are ectotherms. They are cold-blooded. Their body temperatures depend on the temperature of their surroundings. Their bodies receive heat from the outside.

Birds and mammals are endotherms, animals with constant internal body temperatures. They are warm-blooded animals.

VERTEBRATES:CHARACTERISTICS OF FISHES

They are ectothermic animals. Their temperature changes when the temperature of the air or water around them changes.

The bodies are slender enabling the fish to move easily through water.

Fish have fins used for swimming and gliding. Fins help them swim, turn, and stop.

VERTEBRATES:FISHES Hard scales cover their bodies. Fishes

have lateral lines on each side of their bodies which serve as sensors. Fishes use them to feel vibrations from the outside environment, like boats, people, animals, and other things that may be in the water.

Fishes also have gills for breathing. They are located on either side of a fish’s head.

VERTEBRATES:AMPHIBIANS

They are cold-blooded. They spend part of their lives in

water and part on land. They have slimy and cool skin. They are four-legged vertebrates. They depend on water for reproduction. Their eggs have no shells. They lay eggs in a

pond, swamp, or stream to avoid drying. Examples are frogs, toads,

salamanders and newts.

VERTEBRATES:REPTILES

They are ectothermic vertebrates. They have dry, waterproof bodies covered with

scales. Reptiles produce eggs that have a tough

leathery shell. Fertilization takes place inside the reptile’s body.

They have a three-chambered heart like the amphibians.

Examples of reptiles are lizards, snakes, turtles, tortoises, alligators and crocodiles.

VERTEBRATES:BIRDS

They have feathers. They have beaks instead of teeth. They have wings, though not all can fly. They have scales on their legs. The bodies of birds are streamlined to facilitate

flight. They have lightweight bones. Most birds build nests on branches of trees, in a

hole, or in a trunk or in a small hole in the ground. Birds lay eggs with hard shells. Most birds sit on

their eggs until they are hatched.

VERTEBRATES:MAMMALS

They are the most complex of all vertebrates. They have four-chambered heart. Distinct to them is the presence of hair and

mammary glands. The mammary glands, which produce milk to feed their young, are active only in females.

They have more developed brains than any other animals. Humans, however, have the most developed brains which is why they are referred to as the “thinking animal”.

They are warm-blooded. They maintain a constant body temperature.

VERTEBRATES:MAMMALS

Hair or fur keeps the body warm by preventing loss of heat. In the absence of hair on mammals, a layer of fat under the skin keeps the body heat.

They have limbs, which are adapted for varied movements such as running, swimming, climbing, flying or gliding and hopping.

Examples of mammals are: horses, cows, dogs, cats, lions, tigers, kangaroo.

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