Animal Kingdom

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Animals are multicellular eukaryotic heterotrophs that acquire energy and monomers by ingesting the organic molecules of other organisms. Animal cells lack cell walls.

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The cell aggregate plan is the simplest body plan in which the body is just a loose aggregation of cells with little or no coordination. True tissues and organs are absent. Sponges show this type of o…

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The blind-sac plan has a digestive cavity with only one opening to the outside. The same opening is used for ingestion and egestion. It is seen in coelenterates such as Hydra and in flatworms such as …

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The tube-within-a-tube plan has a continuous digestive tube with two openings, a mouth and an anus. It is the most advanced basic body plan and is seen in higher invertebrates and vertebrates.

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In protostomes, the blastopore becomes the mouth and the anus develops later. In deuterostomes, the blastopore becomes the anus and the mouth develops later. Annelids, arthropods and molluscs are prot…

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Symmetry is the arrangement of body parts around an axis or plane. It helps in identifying the basic body pattern of an animal.

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An asymmetrical animal cannot be divided into two equal halves in any plane, as in sponges. In radial symmetry, the body can be divided into similar halves by any plane passing through the centre, as …

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Acoelomate animals have no coelom at all. The space between the ectoderm and endoderm is completely filled by mesoderm. Porifera, Coelenterata and Platyhelminthes are acoelomate.