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Chapter – 4, Animal Kingdom, Introduction, ➢ Animal kingdom is characterized by multicellular, eukaryotic animal, forms., , Basis of classification, ➢ There are some fundamental features common to various individuals in, relation to the arrangement of cells, body symmetry, nature of coelum,, patterns of digestive, circulatory or reproductive systems., ➢ Animal kingdom includes eukaryotic and multicellular organisms., , Levels of organization, ➢ Four levels of organization are found in animals., 1) Cellular level, ✓ The body consists of many cells which may be similar. E.g., sponges., 2) Tissue level, ✓ The cells form poorly defined tissues. E.g. Cnidarians,, ctenophores., 3) Organ level, ✓ Tissues are grouped together to form organs, each specialised for, a particular function. E.g. platyhelminthes., 4) Organ-system level, , ✓ Organs associated to form functional system, each system, concerned with a specific physiological function, e.g., aschelminthes to chordates., ✓ The digestive system may have only a single opening to the, outside of the body that serves as both mouth and anus and is, hence called incomplete., ✓ A complete digestive system has two openings, mouth and anus.

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➢ Similarly, the circulatory system may be of two types:, i) Open type, ✓ The blood is pumped out of the heart and the cells and tissues are, directly bathed in it., ii) Closed type, ✓ The blood is circulated through a series of vessels of varying, diameters., , Body plans, ➢ Animals have three types of body plans, 1) Cell aggregate plan, ✓ The body consists of a cluster or aggregation of cells., ✓ It is found in sponges., 2) Blind sac plan, ✓ The body has a single cavity with one opening to the outside., ✓ The single opening functions as both mouth for ingestion and anus, foe egestion., ✓ It is found in Cnidarians and flatworms., 3) Tube-within-a-Tube plan, ✓ The body has two tubes, one formed by the body wall and the, second formed within it by the digestive tract., ✓ Digestive tract is a continuous tube like structure that has two, openings, a mouth for ingestion and anus foe egestion., ✓ It is of two types:, i) Protostomic plan, • The mouth of the digestive tract develops first in the, embryo and anus is formed later., ii) Deuterostomic plan, • The anus of the digestive tract develops first in the embryo, and the mouth is formed later.

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Symmetry, ➢ Body symmetry is the similarity of parts in different regions and, directions of the body., 1) Asymmetrical or asymmetric, ✓ When the body is not divisible into equal halves by any plane it is, called asymmetrical or asymmetric as found in Amoeba and some, sponges., 2) Radial symmetry, ✓ In this type of symmetry, the body of the individual can be divided, into equal halves by any plane passing through the centre from, top to bottom., ✓ E.g. sponges, jelly fish, star fish., , 3) Bilateral symmetry, ✓ The body can be divided into two equal halves by a single plane, only because the important body organs are paired and occur, on the two sides of a central axis., ✓ It is found in many invertebrates and all vertebrates., , Diploblastic and Triploblastic Organisation, ➢ The embryos of porifers and cnidarians have two germinal layers, the, ectoderm and endoderm. These animals are called Diploblastic.

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➢ The embryos of all other animals have three germinal layers- the, ectoderm, mesoderm and endoderm. These animals are called, triploblastic animals., , Fig. (a) Diploblastic (b) Triploblastic, , Segmentation, ➢ Segmentation is division or differentiation of the body into distinct, portions called segments., ➢ It is of two types: metameric segmentation and pseudometamerism., 1) Metameric segmentation, ✓ It is a type of segmentation where external divisions correspond, to internal divisions., ✓ It occurs in 3 highly organized phyla- Annelida, Arthropoda and, Chordata., ✓ The body is often divided both externally and internally into a, number of segments., 2) Pseudometamerism, ✓ It is found in tapeworms., ✓ The proglottides are budded off from the neck and are not of, embryonic origin hence, this segmentation is called, pseudometamerism.

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Coelom, ➢ Presence or absence of a cavity between the body wall and the gut wall, is very important in classification., ➢ The body cavity, which is lined by mesoderm is called coelom, 1) Acoelomates, ✓ The animals which do not have coelom are called Acoelomates., ✓ E.g. sponges, cnidarians, ctenophores and flat worms., 2) Coelomates, ✓ The true coelom is a body cavity which arises as a cavity in, embryonic mesoderm., ✓ The animals which possess true coelom are called Coelomates., 3) Pseudocoelomates, ✓ The animals which have body cavity, called pseudocoelom, derived, from blastocoel of the embryo are called Pseudocoelomates., ✓ Round worms are Pseudocoelomates., , Fig. (a) Coelomate (b) Pseudocoelomate (c) Acoelomate, , Notochord, ➢ It is a mesodermally derived rod-like structure formed on the dorsal side during, embryonic development in some animals., ➢ Animals with notochord are called chordates and those animals which do not form, this structure are called non-chordates. E.g. porifera to echinoderms.