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04 ANIMAL KINGDOM
ANIMAL KINGDOM 181 SCAN CODE Animal Kingdom Chapter 04 Animal Kingdom Fig 4.1: The Animal Kingdom There are millions of animals, and it is not possible to study each one of them. The organized system of grouping helps us to understand the particular mechanism operating in any one group by examining a few representatives. 1. Basic of Classification  Although there are differences in structures and forms of different animals, yet there are common fundamental features in various individuals. Common fundamental features in various individuals are in relation to:  Arrangement of cells  Body symmetry  Segmentation  Nature of coelom  Notochord  Embryonic layers  Living things such as microbes contain one cell that performs all needed functions, but multicellular organisms are made up of many parts that are needed for survival. These parts are divided into levels of organization.
182 ANIMAL KINGDOM SCAN CODE Animal Kingdom 1.1 Classification on Basis of Level of Organization  Though all members of Animalia are multicellular, all of them do not exhibit the same pattern of organization of cells. Four level of organization are found in animals:  Cellular level: body consists of many cells which may be similar or show minor division of labour. E.g., Sponges  Tissue level: the cells form poorly defined tissues. E.g., Cnidarians, Ctenophores  Organ level: tissues are grouped together to form organs. E.g., Platyhelminthes  Organ-system level: cells are organized into tissues, tissues into organs and organs into organ systems. E.g., Aschelminthes to Chordates Fig 4.2: Diagrammatic representation of level of organization 1.1.1 Body Plan  Animals have three types of body plan:  Cell aggregate plan: the body consists of a cluster or organization of cells. It is found in sponges.  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 for egestion. It is found in cnidarians and most flatworms  Tube-within-a-tube plan: the body has two tubes, one formed by the body wall and the other formed within it by the digestive tract. Digestive tract is a continuous tube-like structure that has two openings, a mouth for ingestion and an anus for egestion. It is found in all the animals of Phylum Aschleminthes to Chordata. 1.2 Classification on Basis of Level of Symmetry  Body symmetry is similarity of parts in different regions and directions of the body.  If a body is divisible into equal halves by one or more planes, it is called symmetrical or symmetric. When a body is not divisible into equal halves by any plane it is called asymmetrical or asymmetric.
ANIMAL KINGDOM 183 SCAN CODE Animal Kingdom Fig 4.3: Diagrammatic representation of symmetry ● Two types of symmetry is usually seen in animals: Radial and Bilateral ● In radial symmetry, the body of the individual can be divided into equal halves by any plane passing through the center from top to bottom e.g., cnidarians (Hydra, Jellyfish), ctenophores and echinoderms (Starfish). Fig 4.4: Radial symmetry in Hydra and Starfish ● In 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. e.g., many invertebrates and all vertebrates. Fig 4.5: Bilateral symmetry in human, housefly and dog 1.3 Classification on Basis of Germ Layers ● A germ layer is a primary layer of cells that forms during embryonic development through the process of gastrulation. These cells give rise to specific tissue, organ and organ systems.