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| Summary |
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 All multicellular animals are now placed in the kingdom of Metazoa. |
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 The multicellular animals show a very specific body organisation which ranges from cellular grade to organ system grade. |
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 Higher in the hierarchy of animal kingdom, one can recognise appearance of specific features like symmetry, body wall and body cavity. |
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 There is also an evolutionary trend in terms of increasing complexity of body organisation, with the appearance of segmentation and cephalisation. |
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 Majority of the multicellular animals (nearly 95%) are invertebrates. |
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 Invertebrates are classified into eight major phyla, from Porifera to Echinodermata. |
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 Members of the phylum Porifera are commonly called sponges. They are cellular grade of animals. |
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 Sponge body shows the presence of numerous incurrent pores called ostia which opine into spongocoel which in turn, opens out through osculum. There are no tissues. |
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 Members of the phylum Coelenterata show the presence of a cavity called coelenteron. |
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 Coelenterates are diploblastic, radially symmetrical animals. |
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 Members of phylum Platyhelminthes are commonly called as flatworms. |
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 Flatworms are triploblastic, radially symmetrical animals which do not possess a body cavity. |
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 Members of the phylum Aschelminthes are commonly called as round worms. |
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 Round worms are pseudocoelomate animals. |
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 Annelids are segmented worms characterised by the presence of a true body cavity (coelom). |
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 Annelids exhibit the presence of a closed type of circulatory system. |
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 Arthropoda represents the biggest phylum in the animal kingdom comprising of nearly 80% of the known animal species. |
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 Arthropods have a chitinous cuticle and many jointed, segmentally arranged appendages. |
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 Molluscs are soft-bodied animals normally found enclosed in a calcareous shell. |
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 Echinoderms are radially symmetrical in the adult stage and bilaterally symmetrical in the larval stages. |
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 Chordates are animals with a notochord, a dorsal tubular nerve cord and pharyngeal gill slits. |
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 Vertebrates represent a major group of chordates. Vertebrates are characterised by the presence of a vertebral column in the adult stage. |
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 Vertebrates are divisible into five classes namely Pises, Amphibia, Reptilia, Aves and Mammalia. |
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 Class Pisces includes aquatic, cold blooded vertebrates, commonly called fishes. |
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 Fishes have an exoskeleton of dermal scales, fins as the locomotor organs and gills as respiratory organs. |
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 Amphibians are cold blooded vertebrates which can live both in water and on land. |
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 Amphibians do not have an exoskeleton. Limbs are the locomotor structures and lungs are the respiratory organs in adults. |
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 Reptiles are cold-blooded terrestrial vertebrates with an exoskeleton of epidermal scales. |
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 Reptiles are lung breathers and have typical pentadactyl limbs. |
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 Birds are warm-blooded vertebrates which show several adaptations towards aerial mode of life. |
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 Birds have an exoskeleton of epidermal feathers. Forelimbs are modified into wings. They have a four chambered heart. |
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 Mammals are warm blooded vertebrates with an exoskeleton of epidermal hairs. |
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 Mammals exhibit the presence of a four chambered heart, enucleate RBC and a muscular diaphragm that separates thorax and abdomen. |
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 Mammals are generally viviparous, giving birth to young ones. |
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