Animal Classification

• Animal classification is the formation of groups and sub-groups of animals depending upon similarities and differences among animals.
• The history of animal classification includes the work of Greek philosopher Aristotle, who classified animals according to criteria like body size, habits, and habitats.
• The new system of animal classification, proposed by Aristotle, is known as the 'Artificial method'.
• Theophrastus, Pliny, John Ray, Linnaeus, and others followed the artificial method of classification.
• A natural system of classification, based on various criteria like body organization, types of cells, chromosomes, bio-chemical properties, etc., was later developed.
• A system of classification based on evolution was also brought into practice, used by Dobzhansky and Meyer.
• Sub-phylum Vertebrata has been further divided into six classes: Cyclostomata, Pisces, Amphibia, Reptilia, Aves and Mammalia.
• Non-chordates are classified into ten phyla: Protozoa, Porifera, Coelentarata / Cnidaria, Platyhelminthes, Aschelminthes, Annelida, Arthropoda, Mollusca, Echinodermata and Hemichordata.
• All chordate animals are grouped together in a single phylum, Phylum- Chordata, which has been divided into three subphyla: Urochordata, Cephalochordata & Vertebrata.
• Notochord is a long rod-like supporting structure present on dorsal side of animal body, which keeps the nerve tissue isolated from the remaining body.
• The five kingdom classification system is based on criteria like Body organization, Body symmetry, Body cavity, Germinal layers, Segmentation, etc.
• Traditional method of animal classification divided Non-Chordates into Characters such as: Body is not supported by rod-like notochord, Pharyngeal gill-slits are absent, Nerve cord; if present, it is on ventral side, Heart, if present, it is on dorsal side.
• Chordates have characters such as: Body is supported by notochord, Pharyngeal gill-slits or lungs are present for respiration, Nerve cord is present on dorsal side of body, Heart is present on ventral side of body.
• Robert Whittaker's five kingdom classification system includes all multicellular animals in Kingdom: Animalia.
• Carl Woese has also proposed the animal classification, which divides the animal kingdom into Non-chordates and Chordates.
• The tail fin of a fish is useful as a steering organ during swimming.
• Fish have paired and unpaired fins for swimming.
• Respiration in fish occurs with gills.
• Diploblastic & acoelomate animals are referred as fish though they are not.
• Class Aves includes vertebrates that are completely adapted for aerial life, are warm blooded (Homeotherms), and their body is spindle-shaped to minimize air resistance during flight.
• Examples of birds include Peacock, Parrot, Pigeon, Duck, Penguin, etc.
• Class Amphibia includes animals that are strictly aquatic during larval life and perform only aquatic respiration, but can live in water as well as on land during adult life and can perform aquatic as well as aerial respiration.
• Examples of amphibians include Frog, Toad, Salamander, etc.
• The body of diploblastic & acoelomate animals is radially symmetrical.
• Water vascular system is present in the body of diploblastic & acoelomate animals.
• Class Mammalia includes animals with the presence of mammary glands, are warm blooded, and their body is divided into head, neck, trunk and tail.
• Diploblastic & acoelomate animals are found in the phylum Coelenterata.
• Examples of reptiles include Tortoise, Lizard, Snake, etc.
• Class Pisces includes Scoliodon (Dog fish).
• Examples of fish include Rohu, Pomfret, Sea horse, Shark, Electric ray, Sting ray, etc.
• Examples of mammals include Elephant, Human, Kangaroo, Dolphin, Bat, etc.
• The exoskeleton of fish is in the form of scales and the endoskeleton is either cartilaginous or bony.
• Hemichordates are also called as ‘acorn worms’.
• Animals in phylum Hemichordata have good ability of regeneration and are mostly unisexual, examples include Starfish, Sea-urchin, Brittle Star, Sea-cucumber, etc.
• Cephalochordata are small, fish-like, marine animals with notochord present in the body during at least any developmental stage, pharynx is very large and contains gill-slits, these animals are unisexual, examples include Amphioxus.
• Urochordata are small, fish-like, marine animals with notochord present throughout the body length, pharynx is very large and contains gill-slits, these animals are unisexual, examples include Amphioxus.
• Notochord is present in proboscis region only in Hemichordates, hence they are called as hemichordates.
• Animals in phylum Chordata have a supporting notochord in their body, all chordates are included in the same phylum, the phylum Chordata is classified in to three subphyla, Urochordata, Cephalochordata, and Vertebrata/Craniata.
• These animals are triploblastic, bilaterally symmetrical and eucoelomate.
• Vertebrata/Craniata are animals where notochord is replaced by vertebral column, head is well developed, brain is protected by cranium, endoskeleton is either cartilaginous or bony, some chordates are jaw-less (Agnatha) whereas some are with jaws (Gnathostomata), these are marine animals, their body is covered by skin-like test or tunic, larvae of these animals are freely swimming and notochord is present in only tail region of larvae, these animals are generally hermaphrodite, examples include Herdmania, Doliolum, Oikopleura, etc.