Animal kingdom Basis of classification There are certain

Animal kingdom

Basis of classification There are certain features which are used as the basis for animal classification. They are 1. Levels of organisation-cellular level, tissue level, organ level & organ system level. 2. Symmetry-asymmetrical, radial symmetry, bilateral symmetry. 3. Diploblastic & triploblastic organisation.

4. Coelom- coelomates, pseudocoelomates & acoelomates. 5. Segmentation-presence(metamerism) or absence. 6. Notochord –chordates & non chordates. Based on these features, animals are classified into different phylum 1. Phylum Porifera 2. Phylum Coelenterata(Cnidaria) 3. Phylum Ctenophora 8. Phylum Mollusca 4. Phylum Platyhelminthes 9. Phylum 5. Phylum Aschelminthes Echinodermata 6. Phylum Annelida 10. Phylum hemichordata 7. Phylum Arthropoda 11. Phylum chordata

• Phylum Porifera (e. g. sycon, Euspongia, Spongilla) 1. Commonly known as sponges. 2. Generally marine, asymmetrical & have cellular level of organisation. 3. Water enters through minute pores in the body wall called ostia into a central cavity spongocoel & goes out through osculum. Choanocytes or collar cells line the spongocoel. 4. Digestion is intracellular. 5. Body supported by a skeleton made up of spicules. 6. Sexes not seperate(hermaphrodite), eggs & sperms are produced by the same individual. Asexual reproductionfragmentation. Sexual reproductionformation of gametes. 7. Fertisation is internal & development includes a larval stage.

• Phylum Coelenterata(Aurelia, Adamsia) 1. They are mostly marine, sessile or free swimming, radially symmetrical animals. 2. Are diploblastic with tissue level of organisation. 3. Tentacles have cnidoblasts or cnidocytes which contain stinging capsules or nematocytes. 4. Digestion is extracellular & intracellular. They have a central gastrovascular cavity with a single opening called hypostome. 5. Skeleton composed of calcium carbonate in case of corals. 6. They exist in 2 body forms-polyp & medusa. Polyp is a cylindrical & sessile form e. g. Hydra, Adamsia. Medusa is umbrella shaped & free swimming. e. g. aurelia Some exist in both forms exhibiting alternation of generation(metagenesis), polyp undergo asexual reproduction producing medusa & medusa sexually produce polyp. e. g. Obelia

• Phylum. Ctenophora (Pleurobrachia, Ctenoplana) 1. Commonly known as sea walnuts or comb jellies. 2. They are marine, radially symmetrical, diploblastic organisms with tissue level of organisation. 3. The body bears 8 rows of ciliated comb plates which help in locomotion. 4. Digestion is both extracellular & intracellular. 5. Bioluminescence is well marked in ctenophores. 6. Sexes are not separate. 7. Reproduction is sexual. 8. Fertilisation is external & indirect development,

Phylum Platyhelminthes (Teania, Fasciola) 1. They have dorsoventrally flattened body, hence called flat worms. 2. They are mostly endoparasites found in animals including human beings. 3. Flatworms are bilaterally symmetrical, triploblastic & acoelomate animals with organ level organisation. 4. Absorb nutrient from host. Hooks & suckers present in parasitic forms. 5. There are specialised cells called Flame cells which help in osmoregulation & excretion. 6. Sexes not separate, fertilisation is internal & development indirect.

• Phylum Aschelminthes (Ascaris, Ancylostoma) 1. Body is circular in cross section & hence called round worm. 2. They are free living, aquatic or terrestrial or parasitic forms. 3. They are bilaterally symmetrical, triploblastic, pseudocoelomate animals with organ system level of body organisation. 4. Alimentary canal is well developed with a muscular pharynx. 5. There are excretory tubes which removes waste through body pores. 6. Sexes separate, fertisation is internal & development may be direct or indirect.

• Phylum Annelida (Nereis, Pheretima, Hirudinaria) 1. They may be aquatic or terrestrial, freeliving or parasitic. 2. Body is divided into segments or metameres, hence the name annelida. 3. They are triploblastic, metamerically segmented coelomate animals with bilateral symmetry & organ system level of body organisation. 4. Lateral appendages called parapodia which help in swimming. 5. A closed circulatory system is present. 6. Osmoregulation & excretion is done with the help of specialised structures called nephridia. 7. Neural system well developed. 8. Dioecious or monoecious. Reproduction is sexual.

• Phylum Arthropoda(Apis, Bombyx, Aedes) 1. They have jointed appendages, hence the name arthropoda. 2. They are bilaterally symmetrical, triploblastic, segmented, coelomate animals with organ system level of organisation. 3. The body covered with exoskeleton is divided into 3 regions- head, thorax & abdomen. 4. Respiratory organs are gills, book lungs or trachea. 5. Circulatory system is open type. 6. Sensory organs are antennae, eyes. 7. Balance organs called statocysts are present. 8. Excretion through tubule like structures called malpighian tubules. 9. Mostly dioecious. Fertilization is internal. Mostly oviparous. Development is direct or indirect. 10. Largest phylum of animalia.

• Phylum Mollusca(Pila, Octopus) 1. They are terrestrial or aquatic, bilaterally symmetrical, triploblastic, coelomate animals with organ system level of organisation. 2. Unsegmented body is covered by a calcareous shell & is divided into head, muscular foot & visceral hump. 3. A soft & spongy layer of skin forms a mantle over the visceral hump. The space between hump & mantle is called mantle cavity. 4. Respiration & excretion is well developed. 5. The anterior head like structure have sensory tentacles. Mouth has rasping organ called radula. 6. Dioecious, oviparous& indirect development.

• Phylum Echinodermata (Asterias, Ophiura) 1. These animals have spiny ossicles on their body, hence the name echinodermata. 2. They are marine, radially symmetrical(larvae bilaterally symmetrical), triploblastic, coelomate animals. 3. Digestive system is complete with mouth on the lower side & anus on the upper side. 4. Presence of water vascular system which helps in locomotion, respiration & capture & transport of food. 5. Excretory system is absent. 6. Sexes separate. Reproduction sexual. Fertilisation is external. Development is indirect with free swimming larva.

Phylum Hemichordata (Balanoglossus, Saccoglossus) 1. They are worm like marine animals, bilaterally symmetrical, triploblastic, coelomate animals with organ system level of organisation. 2. The body is cylindrical & is composed of an anterior proboscis, a collar & a long trunk. 3. Circulatory system is of open type. 4. Respiration takes place through gills. 5. Excretory organ is proboscis gland. 6. Sexes separate. Fertilisation external. Development is indirect.

• Phylum Chordata Chordates are characterised by the presence of: 1. A notochord 2. A dorsal hollow nerve cord. 3. Paired pharyngeal gill slits.

• Class Cyclostomata (Petromyzon, Myxine) 1. They are ectoparasites. 2. They have a elongated body bearing 6 -15 pairs of gill slits for respiration. 3. Circular mouth without jawssucking in function. 4. Body is devoid of scales & fins. 5. Circulation is of closed type. 6. Cyclostomes are marine but for spawning migrate to freshwater, after spawning they die. Larvae undergoes metamorphosis & return to ocean.

Class Chondrichthyes(Scoliodon, Pristis) 1. They are marine animals with streamlined body & cartilaginous endoskeleton. 2. Poikilothermic animals with persistent notochord. 3. Mouth is located ventrally, gillslits separate, operculum absent. 4. The skin is tough with placoid scales. 5. Jaws are very powerful. 6. Air bladder absent. 7. Heart is two chambered-one auricle & one ventricle. 8. Some have electric organs-Torpedo & some with poison sting-Trygon. 9. Sexes separate. Internal fertilisation. Mostly viviparous.

• Class Osteichthyes (Exocoetus, Hippocampus, Labeo, Catla) 1. Marine & fresh water fishes, stream lined body with bony endoskeleton. 2. Poikilothermic animals. 3. Mouth is terminal, four pairs of gills covered with operculum. 4. Skin is covered with cycloid or ctenoid scales. 5. Air bladder is present regulating buoyancy. 6. Heart is two chambered. 7. Sexes separate. Fertilisation is external. Mostly oviparous.

• Class Amphibia (Rana, Hyla, salamandra) 1. Poikilothermic animals , aquatic as well as terrestrial with two pairs of limbs. 2. Body divisible into head & trunk. Tail present in some. 3. Skin without scales. 4. Eyes have eyelids. 5. Tympanum represents the ear. 6. Respiration is by gills, lungs & through skin. 7. Alimentary canal, urinary & reproductive tracts open into a common chamber called cloaca. 8. Respiration is by gills, buccal & through skin. 9. The heart is three chambered-2 auricles & 1 ventricle. 10. Sexes separate. Fertilisation external. Oviparous. Development indirect.

• Class Reptilia (Chelone, Chameleon, Alligator) 1. Creeping or crawling mode of locomotion & hence the name characterised by two pairs of limbs. 2. Mostly terrestrial, body is covered by dry & cornified skin-presence of scales or scutes. 3. Tympanum represents the ear. 4. Heart is three chambered. One exception is crocodile which is 4 chambered. 5. Sexes separate. Fertilisation internal. Oviparous. Development direct.

• Class Aves (Pavo, Psittacula, Struthio, Corvus) 1. Homeiothermic animals characterised by the presence of feathers & beaks, capable of flying. 2. The fore limbs are modified into wings & hind limbs generally have scales & are modified for walking, swimming or clasping the branches. 3. Skin is dry without glands except the glands at the base of the tail. 4. Bony endoskeleton with air cavities-pneumatic bones. 5. Heart is completely four chambered. 6. Air sacs are connected to lungs which also aid in respiration. 7. Sexes separate. Fertilisation internal. Oviparous. Development direct.

• Class Mammalia (Pteropus, Ornithorhynchus, Macropus) 1. Characterised by the presence of mammary glands by which the young ones are nourished. 2. They have two pairs of limbs adapted for walking, running, climbing, burrowing e. t. c. 3. Homeiothermic animals with hairs on their skin. 4. External ears or pinnae is present. 5. Different types of teeth present. 6. Heart four chambered. 7. Respiration by lungs. 8. Sexes separate. Fertilisation internal. Viviparous. Development direct.