WBCS Preliminary (Biology): Animal Kingdom

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There are 10 major phyla in the animal kingdom from Protozoa to Chordata.
  1. Protozoa : This most primitive unicellular organisms which reproduce by fission, budding,spores or sexually. e.g. Amoeba, Entamoeba, paramecium, vorticella, plasmodium, Euglena & trypanosoma. They move a variety of ways. The ameba has a false foot that extends as it moves. The paramecium is covered with hairs and the euglena has a whip-like tail(flagella) to move. A protozoa takes in oxygen through the cell membrane and gives off carbon dioxide through the cell membrane. Some protozoans are harmful to man as they can cause serious diseases.
  2. Porifera (Sponges): These are most primitive of multi cellular animals. They live in water bodies. Body with a large number of incurrent pores called ostia leading into a spongocoel through a system of canals, Spongocoel opening out by one or two large excurrent pores called oscula. Respiration and excretion by simple diffusion.
  3. Cnidaria (Coelenterata): These are mostly marine species except hydra which is fresh water form. Body has a mouth at the oral end which leads into a spacious cavity called gastrovascular cavity or coelenteron. Respiration and excretion by simple diffusion. Important coelentrates are coral, hydra, jellyfish, sea anemone, Portuguese man of war.
  4. Platyhelminths(Flat worms): Flat worm is a common name for soft bodied, usually parasitic animals, the simplest of animals possessing heads. Respiration by simple diffusion. They are bilaterally symmetrical and somewhat flattened and are elongated. E.g. Tape worm, flukes.
  5. Nemathelminthes(round worms): These are roundworms which are usually found in soil, water, plants and in animals as a parasite. Body is long, cylindrical, fusiform (pointed at both the ends). Respiration by simple diffusion. A roundworm has a definite digestive system that runs the length of their bodies. It has a mouth, pharynx, intestine and anus. e.g. Ascaris(round worm),oxyuris(pinworm), ancylostoma(hook worm),wucheria(Filaria worm).
  6. Annelida: Free-living, terrestrial or aquatic form (freshwater or marine). Body is long, cylindrical and metamerically segmented. Body wall consists of cuticle, epidermis and musculature. Respiration is either through skin or through gills. Body has a true coelom. E.g. earth worms, leech and clamworm.
  7. Arthropods: This phylum is the largest in the animal kingdom comprising of more than 75% of the animal species that have been identified. Body is elongated and segmented, usually distinguished into regions like head, thorax and abdomen. The arthropods are the first animal group to have jointed legs. Circulatory system is of open type. Blood flows freely in the body cavity (hemocoel). Respiration through gills, or trachea or book lungs. The major groups are:
    • Insects : The largest class of arthropods. They have six legs and three body parts, a head, a thorax and an abdomen. All insects grow from eggs. A insect has a circulatory system that carries food, but not oxygen throughout its body. Since it does not carry oxygen, insect blood is green, not red like mammal blood. Example- butterfly, bee, ant, beetle, dragonfly, termite, grasshopper and true bug etc.
    • Arachnids: The annelids are similar to insects. However, they have eight legs, wings are different and they have no antenna. The arachnids are spiders, scorpions, etc
    • Crustaceans: These are predominantly aquatic arthropods with protective carapace and compound eyes. E.g. Prawns, Lobsters and Crabs.
    • Myriapods: include millipedes and centipedes. The centipedes have two pairs of legs per segment while millipedes have one pair.
  8. Mollusca : It is the common name for members of a phylum soft-bodied animals with a hard external shell (so called shell fishes). It is the second largest kingdom after arthropods. The three major groups are gastropods, bivalves and cephalopods. Respiratory organs are in the form of gills called ctenidia. Example-snails, slugs, clam, cockle, mussel, oyster, scallop, shipworm, squid, octopus, and nautilus.
  9. Echinoderm: It consists of phylum of marine animals such as starfish, brittle stars, sea urchins, sand dollars and sea cucumbers. Body is represented by a central disc covered by ossicles with spines called pedicellaria. Disc may bear extensions called arms. Tube feet are present for locomotion and respiration. Tube feet are extended and retracted by variation in hydraulic pressure of the fluid in them and contraction of their muscles. A Echinoderm is a male or female. The males and females discharge their eggs and sperm into the water where they are fertilized. A female can release one hundred million eggs at once.
  10. Chordate: Presence of a solid supporting structure on the dorsal side of the body called notochord lying above the gut and beneath a single hollow dorsal nerve cord. The Phylum chordate has been divided into Proto chordate and Vertebrate.
    • Proto Chordate: They are primitive lower chordates possess notochord but lacks vertebral column or back bone.
    • Vertebrate: It represents the largest group of chordates.
      • Agnatha: They are fish like forms with the absence of Jaws and scales. The best examples of this type are lamprey and the hagfish.
      • Gnathostomata: These are vertebrates with jawed mouth. These are subdivided into fishes, amphibians, reptiles, birds and mammals.
        1. Fishes: These are diverse group of cold blooded animals that live and breathe in water. Most fish have gills for breathing, two chambered heart, fins for swimming, scales for protection, and a streamlined body for moving easily through the water.
        2. Amphibians: Amphibian means both sides of life. it begins its life in the water and then finishes it mainly on land. It uses gills in larval stage (tadpole) and lungs and skins in the adult stage. Their heart is three chambered. Skin is often kept moist for gas exchange. These are cold blooded animals and have to be near water to complete their life cycle.Example--Frogs, toad, Salamander, caecilians, sirens etc.
        3. Reptiles: Reptiles are cold blooded animal with tough, dry skin covered with horny scales adapted for life in dry places. Some forms are aquatic. Reptiles breathe air with lungs alone. They have teeth except in tortoises and turtles. They have three chambered heart (crocodile has a four chambered heart). The females eggs are fertilized in her body by the male. The eggs are laid in a shell that has a leathery covering to protect it in the wilds. E.g. turtles, lizards, snakes, crocodiles, gavial (Gharial),alligators and dinosaurs.
        4. Birds: They are unique in the fact that they are covered with feathers and fly. They are descended from reptiles, feathers are modified limbs and their eggs resemble reptilian eggs. But like mammals they are warm blooded and have four chambered heart. The bones of many adult birds are hollow rather than filled with marrow, making them lighter and enabling them to disperse heat in flight.
        5. Mammals: Mammals are warm blooded animals having distinctive characteristics such as milk producing mammary glands, hair on their body, external ears, sweat glands, give birth to young rather laying eggs and nurse their young.

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