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Introduction to Zoology

Zoology – The systematic study of the structure, form and distribution of animals is called Zoology.

The animal kingdom can be classified over two sub groups – 1. Unicellular animal; and 2. Multi-cellular animal.

Unicellular animals are kept under single phylum protozoa while multi-cellular animals are grouped over 9 phylums. Following given classification of animals according to phylum to which they belongs.

Phylum Protozoa- Unicellular organisms belongs to this phylum. The main features of phylum protozoa are listed below.

•    It has only one cell.
•    It’s cytoplasm may contain one or more nuclei.
•    All metabolic actions like eating, digestion, respiration, excretion and reproduction occurs inside a single cell only.
•    In unicellular organisms respiration and excretion takes place by diffusion, example; Amoeba, Euglena, Trypanosoma etc.

Phylum Porifera- Marine water animals comes under this category, these have pores on their body. The main features of phylum porifera are listed below.

The animals of this group are multi-cellular but cells do not present regular tissues.
Numbers of pores called Ostia found on body walls.
The skeleton is build of smaller calcareous or silicon spicules, example; Sycon, sponge etc.

Phylum Coelenterate – The main features of phylum coelenterate are listed below-

The animals of this group are aquatic and diploblastic.
Around the mouth of these animals found thread like structure, this is called tentacles and helps in holding the food.
Body radial symmetry.
Specialized cnidoblast cells are found help in catching the food, example; Hydra, Jelly Fish, Sea Anemone, etc.


Phylum Platyhelminthes- Flat worm comes under this category. The main features of the phylum are listed below-

•    Platyhelminthes are bilaterally symmetrical animals
•    The left and right sides of these animals are mirror images of each other;
•    These animals have distinct top and bottom surfaces and distinct head and tail ends.
•    Like other bilaterians, they have three main cell layers, while the radially symmetrical cnidarians and ctenophores (comb jellies) have only two cell layers.
•    Unlike other bilaterians, Platyhelminthes have no internal body cavity, so are described as acoelomates.
•    Their bodies are soft and unsegmented. They also lack specialized circulatory and respiratory organs.

Examples of Phylum Platyhelminthes are – Planaria, Liver Fluke, Tape worm etc.

Phylum Ascheleminthes: Round Worm come under this phylum. The main features are listed below-

•    Mostly parasitic in animals and plants, a few free living called as flukes.
•    Body is long, cylindrical, fusiform i.e. pointed at both the ends.
•    Body wall is composed of cuticle, epidermis and musculature.
•    Presence of a false body pseudocoelom not lined by epithelium.
•    Digestive system is complete.
•    Respiration by simple diffusion.
•    Nervous system consists of a nerve ring and many longitudinal nerve cords.
•    Only sexual reproduction. Sexes are separate with sexual dimorphism. Males are usually shorter than females.

Phylum Annelida- Main features of this phylum are listed below-
•    Bilaterally symmetrical and vermiform.
•    Body has more than two cell layers, tissues and organs.
•    Body cavity is a true coelom, often divided by internal septa.
•    Body possesses a through gut with mouth and anus.
•    Body possesses 3 separate sections, a prosomium, a trunk and a pygidium.
•    Has a nervous system with an anterior nerve ring, ganglia and a ventral nerve chord.
•    Has a true closed circulatory system.
•    Has no true respiratory organs.
•    Reproduction normally sexual and gonochoristic or hermaphoditic.
•    Feed a wide range of material.
•    Live in most environments.

Phylum Arthropoda- The main features of this phylum group are listed below-

•    Bilaterally symmetrical (in most cases).
•    Body has more than two cell layers, tissues and organs.
•    Body cavity a true coelom.
•    Most possesses a through straight gut with an anus (in most cases).
•    Body possesses 3 to 400+ pairs of jointed legs.
•    Body possesses an external skeleton (in most cases).
•    Body is divided in 2 or 3 sections.
•    Nervous system includes a brain and ganglia.
•    Possesses a respiratory system in the form of tracheae and spiracles (in most cases).
•    Possesses a open or lacunnar circulatory system with a simple heart, one or more arteries, and no veins, (in most cases).
•    Reproduction normally sexual and gonochoristic, but can be parthenogenetic.
•    Feed on everything.
•    Live everywhere.
Note – 1. Insects has 6 feet and 4 wings. 2. Cockroach heart has 13 chambers. 3. Ant is social animal and symbolizes labor division. 4. Termite lives in colony.

Phylum Mollusca- Soft bodied animals comes under this category. The main features are listed below-
•    The body is soft divided into head and foot.
•    Mantle is present which secrets a hard calcareous cell.
•    Alimentary canal is well developed.
•    Respiration takes place through gills or ctenidia.
•    Blood is colorless.
•    Excretion takes place through Kidneys.


Phylum Echinodermata- The main features of Phylum Echinodermata are mentioned below:

•    All echinoderms are marine organisms. In the larval stage, most echinoderms are bilaterally symmetrical.
•    Most adults are radially symmetrical.
•    They have a ventral mouth, an internal skeleton of calcium carbonate plates, and a water vascular system consisting of tube feet, radial canals, and a ring canal for movement.

Phylum Chordata- The animals belonging to this phylum are called chordates. Taxonomically the phylum Chordata includes three subphyla: Tunicata; Cephalochordata, comprising the lancelets; and the Craniata, or Vertebrata. The common attributes of the Chordata include having, for at least some period of their life cycles, a notochord, a hollow dorsal nerve cord, pharyngeal slits, an endostyle, and a post-anal tail. The phylum Hemichordata has been presented as a fourth chordate subphylum, but it now is usually treated as a separate phylum.


Principal Groups of Phylum Chordata

1. Pisces- Main Characteristics – Aquatic Life

•    These are cold blooded animals.
•    Heart of these animals pumps only impure blood and have 2 chambers.
•    In these animals respiration happens through gills.
•    Example of these animals are Hippopotamus, Scoliodon, Torpedo, etc.

Amphibia- The Principal characteristics of these animals are described below-
These animals lives on land and water both.
Like Pisces, amphibians are also cold blooded animals.
In these animals respiration happens through gills, skin and lungs.
The heart of these animals has 3 chambers; two auricles and one ventricle.
Some of the examples are frog, necturus, toad etc.

Reptilia- The Principal characteristics of these animals are described below-

•    These are crawling animals.
•    These includes land vertebrates, cold blooded, terrestrial and aquatic vertebrates.
•    These contain two pair of limbs.
•    The skeleton is completely flexible.
•    Respiration in these animals takes place through lungs.
•    The eggs of these animals covered with shell made of calcium carbonate.
•    The examples of Reptilia are – lizard, snake, tortoise, crocodile, turtle, sphenodon etc.

Aves- The Principal characteristics of these animals are described below-

•    These are warm blooded tetrapod vertebrates with flight adaptation.
•    Fore-feet modified into wings to fly.
•    Body is boat shaped and divisible into head, neck, trunk and tail.
•    Respiratory organ is lungs.
•    Have no teeth; beak helps in feeding.
•    Some of the examples are – crow, peacock, parrot etc.

Some Amazing Facts About Birds

•    Flightless birds- ostrich, emu, cassowary, rhea, kiwi, and penguin

•    Smallest Bird- Male bee hummingbirds (mellisuga helenae), which live in Cuba.

•    Smallest Parrot- Pygmy parrots of Papua and nearby islands.

•    Fastest Swimming Bird- Gentoo Penguin found on the Antarctic Islands can swim 40 km per hour.

•    Largest Carnivorous Bird- Titanis Walleri. This bird is known from the early Pleistocene (Ice Age) of Florida.

•    Tallest Flying Birdscrane- The largest cranes (family Gruidae) can be almost 6 ft. 6 in. tall.

•    Heaviest Flying Birds- The Kori Bustard or paauw (Ardeotis Kori) of northeast and southern Africa and the great bustard (Otis tarda) of Europe and Asia weigh about 40-42 pounds.

•    Heaviest Parrot- Flightless Kakapo around 7lbs in weight; New Zealand

•    Longest Feathers- The phoenix fowl or Yokohama chicken

•    Longest Bills- The bill of the Australian pelican (Pelicanus conspicillatus) is 13-18.5 inches long.

•    Only Nostrils on tip of Beak- The Kiwi is the only bird with nostrils at the tip of its beak.

•    Biggest Eyes - The ostrich has the largest eyes of any land animal. Each eye can be up to 2 inches in diameter.

•    Best Talker- The African Grey Parrot


Mammalia- The Principal characteristics of these animals are described below-

•    Oil glands and sweat glands are found on skin.
•    All these animals are warm blooded.
•    Heart of these animals divided into two chambers.
•    Tooth comes twice in these animals (Diphyodont).
•    These found no nucleus in red blood cell; camel and lama are exceptions.
•    Skin of mammals has hairs.
•    External ear is present

Mammals are divided into three sub classes-

1.    Prototheria – It lays eggs; example – Echinda
2.    Metatheria- It bears the immature child; example – Kangaroo.
3.    Eutheria- It bears the well developed child; example- human.

The Animal Tissues

The animal tissues can be divide over following categories-

Epithelial tissue- The Epithelial tissue covers body surfaces and lines body cavities. Functions include lining, protecting, and forming glands. Three types of epithelium occur:
•    Squamous epithelium is flattened cells.
•    Cuboidal epithelium is cube-shaped cells.
•    Columnar epithelium consists of elongated cells.

Any epithelium can be simple or stratified. Simple epithelium has only a single cell layer. Stratified epithelium has more than one layer of cells. Pseudostratified epithelium is a single layer of cells so shaped that they appear at first glance to form two layers.

Connective tissue – The Connective tissue serves many purposes in the body:

•    binding
•    supporting
•    protecting
•    forming blood
•    storing fats
•    filling space

Connective cells are separated from one another by a non-cellular matrix. The matrix may be solid (as in bone), soft (as in loose connective tissue), or liquid (as in blood). Two types of connective tissue are Loose Connective Tissue (LCT) and Fibrous Connective Tissue (FCT). Fibroblasts (LCT) are separated by a collagen fiber-containing matrix. Collagen fibers provide elasticity and flexibility. LCT occurs beneath epithelium in skin and many internal organs, such as lungs, arteries and the urinary bladder. This tissue type also forms a protective layer over muscle, nerves, and blood vessels.

Muscle tissue – The Muscle tissue facilitates movement of the animal by contraction of individual muscle cells (referred to as muscle fibers). Three types of muscle fibers occur in animals (the only taxonomic kingdom to have muscle cells):

•    skeletal (striated)
•    smooth
•    cardiac

Nervous tissue – The nervous tissue, functions in the integration of stimulus and control of response to that stimulus. Nerve cells are called neurons. Each neuron has a cell body, an axon, and many dendrites. Nervous tissue is composed of two main cell types: neurons and glial cells. Neurons transmit nerve messages. Glial cells are in direct contact with neurons and often surround them.