Animal Classification

 Animal Classification

 

l   According to recent studies, estimated number of animal species on the earth is approximately seven millions.

l   It is impossible to study each and every species together. However, the systematic grouping, i.e. classification will make it very easy to study such vast variety of animals.

l   Greek Philosopher Aristotle was the first to perform animal classification. Classification proposed by him is known as ‘Artificial Method’.

l   Besides Aristotle, this method was followed by Theophrastus, Pliny, John Ray, Carl Linnaeus, etc.

l   Later on, ‘Natural System of Classification’ was followed. It was based on the various criteria like body organization, types of cells, chromosomes, bio-chemical properties, etc.

l   By the time, system of classification based on evolution was also brought into practice. It was used by Dobzhansky and Meyer.

l   Recently Carl Woese has also proposed the animal classification.

l   Traditionally, depending upon presence or absence of the notochord, the animal kingdom has been classified into two groups: Non-chordates and Chordates.

l   ‘Non-Chordates are further classified into 10 phyla. Protozoa, Porifera, Cnidaria, Platyhelminthes, Aschelminthes, Annelida, Arthropoda, Mollusca, Echinodermata, Hemichordata.

l   Chordates are further classified into Urochordata, Cephalochordata and Vertebrata.

l   Sub-phylum Vertebrata is divided into six classes Cyclostomata, Pisces, Amphibia, Reptilia, Aves and Mammalia.

l   According to Robert Whittaker, all multicellular animals are included in Kingdom Animalia.

l   There are different criteria for classifying animals. They are Grades of Organization, Body symmetry, Germ layers, Body cavity (Coelom), Body segmentation.

 

Characteristics of Non-Chordates
Phylum	Habitat	Body structure	Reproduction	Locomotion	Special features	Examples
Porifera	Aquatic : Marine/ fresh water	Simplest body plan, Assymmetrical body with many pores on body.	l Asexual reproduction: budding l Sexual reproduction/ Regeneration	Sedentary locomotion (attached to substratum)	l  Special cells: l  Spongy body supported by spicules spongin fibres: CaCO3 and Silica	Sycon, Euspongia (Bath sponge) Hyalonema, Euplectella
Cnidaria or Coelenterata	Aquatic : Mostly marine/few fresh water	Cylindrical/ umbrella like: Polyp/Medusa	Asexual/sexual	Sedentary free swimming	Cnidoblast bear (stinging cells) tentacles. It is use for capturing prey.	Hydra, (Sea anemone) (Portuguese man of war) Physalia Jellyfish, Corals, etc.
Platyhelminthes	Free/living/ parasitic/ terrestrial aquatic	Slender, Leaf like flat bodies	Bisexual/sexual animals	Swimming	Flat body is a typical character	Planaria, Liver fluke, Tapeworm, etc.
Aschelminthes	Endoparasitic free living	Cylindrical, long thread like	Unisexual/sexual animals	Swimming	Non-segmentated bodies with cuticle.	Ascaris (Round worm Filarial worm Loa loa (Eye worm)
Annelida	Free swimming marine, terrestrial , few ectoparasitic	Metameric segmented body cylindrical	Bisexual/sexual animals	Setae, Parapodia and Suckers creeping mode	Special cuticle over body	Earthworm Nereis, Leech.
Arthropoda	Ranging from deepest oceans to highest mountains	Different types of body structures, like hard exoskeleton, eight legged, flying insects, etc.	l Sexual/unisexual animals l Metamorphosis: Egg, à larvae à à pupae à adult	Swimming/creeping	l  Largest animal phylum l  Chitinous exoskeleton, jointed paired appendages and segmented body.	Crab, prawn, spiders, scorpions. All insects (cockroach, butterfly, ants), Centipede, Millipede.
Mollusca	Marine/fresh water/terrestrial	Soft bodies, Slimy, Some have shells	Unisexual/sexual animals	Swimming/creeping by foot	l  Body divisions: Head, foot and visceral mass. l  Second largest animal phylum	Oyster, Bivalves, Snail, Octopus, etc.
Echinodermata	Only marine	Skeleton of calcareous spines, radial animals	l Sexual l Good regeneration capacity	l  Some sedentary l  Some swim l  Some creep by tube feet.	Spiny bodies with oral and aboral surfaces.	Star fish, Sea urchin, Brittle star, Sea cucumber
Hemichordata	Only marine	l Proboscis collar and trunk. l Notchord in probosciis	Sexual/Unisexual bisexual animals	Burrowing in sand.	l  Connecting link between the nonchordates and chordates l  Presence of pharyngeal gill slits.	l  Balanoglossus, l  Saccoglossus commonly called acron worms.

 

 

Characteristics of chordates
Class	Habitat	Body structure	Appendages	Mode of respiration	Resproductio	nT emperatur Regulation	e      Examples
Cyclostom	alt aAquatic : Ectoparasite/ marline	l  So ft skin, no l  Jaw less mout and sucker	s lc a Pl easired happendages	l  Gills	l  Oviparous (lays eggs)	l  Cold blooded	l  P etromyzon Myxine, etc.
Pisces	l  Aquatic: Marine/fresh w ater	l  Exoskeleton: Scales l  Endoskeleton: Cartilage/bones l  Stream lined body	l  Paired and unpaired appendages	l  Gills	l  Oviparous (lays eggs)	l  Cold blooded	l  Scoliodon, pomfret, Bombay duck. Sea horse, Electric ray, etc.
Amphibia	l  Land and water	l  No exoskeleton l  Soft and moist skin l Body differentiated into head and trunk	l  Two pairs of limbs	l  When in water Tadpole/ larvae: gills Adult: Gills l When on and: l  lungs	l Metamorphosis: E.g. Larva, adult	l  Cold blooded	l  Frog, Toad, Salamandar, etc
Reptilia	l  Mainly terrestrial, some aquatic	l  Skin is dry and scaly l  Body differentiated into head, neck and trunk	l  Two weak pairs of limbs	l  Lungs	l  Egg, young, adult	l  Warm blooded	l  Tortoise, lizard, snake, etc.
Aves	l  Terrestrial, some fly	l  Exoskeleton in form of feathers l  Streamlined body l  Body differentiated into head, neck and trunk	l  Forelimbs modified into feathers	l  Lungs (air sacs)	l  Oviparous (lays eggs) l  Parental care	l  Warm blooded	l  Peacock, Parrot, Crow, Duck, Penguin, etc.
Mammalia	l  Mainly terrestrial, some aquatic, few aerial	l  Exoskeloton in form of hair, fur, wool l  Body differentiated into head, neck, torso and tail	l  Two pairs of limbs: hands/legs	l  Lungs (Diaphragm)	l  Majority viviparous, few oviparous (lays eggs)	l  Warm blooded	l  Kangaroo, Dolphin, Bat, Dog, Human, etc.