Introduction
The kingdom Animalia includes all animals. The word animal is derived from the Latin word anima which means breath or soul. Animals are multicellular ingestive heterotrophic organisms that are developed by the fusion of haploid "" nonmotile eggs and haploid "n" motile sperms.
They were originated from animal-like protists. The branch of biology which deals with the study of animals is called Zoology.
9.1 Characteristics of Animals
All animals are eukaryotic multicellular heterotrophic organisms, found almost in all types of habitats (such as terrestrial, music, aerial, arboreal, etc). Most animals are motile, and some are sessile but their larval stage is motile, few are parasites and their size ranges from microscopic (words) to very large in size (Blue whale) almost 150 tons.
Locomotion, mostly utilizing muscle fibers. Most animals contain two sets of chromosomes in their body cell. They respire both aerobically and anaerobically.
The body of animals may be from soft to hard, diploblastic or triploblastic, either radially symmetrical or bilaterally symmetrical, few are asymmetrical. Their body is mostly covered with shells, chitin, bony plates, scales, furs, feathers, etc.
Bilateral symmetrical animals may be either acoelomates (Platyhelminthes) pseudocoelomates (Nematodes) or coelomates (from Annelida to chordate). They possess only ingestive heterotrophic nutrition. Animals have either an incomplete digestive system (single
opening) or a complete digestive system, a tube-like digestive system with mod anus at opposite ends. The excretory system is well developed in most animals while absent in poriferans and coelenterates. The nervous system in the peripherals is absent while in the coelenterates neuron set is present.
It is well developed in most animals, sory cells or sense organs are also present. The respiratory system is mostly present L., from arthropods to chordates, while lower non chordates respire only by diffusion from surrounding
The skeletal system is recorded in all animals, which is spicules or spin fibers in periferns. In most invertebrates hydrostatic skeleton is present. While endorsed and recorded in a few molasses (cuttlefish), echinoderms, and in all verses Exoskeleta is also present in many invertebrates (Arthropods, Mollusca), it is also present in mo chordates.
The circulatory or blood vascular system is well developed from Annelida Chordata, while in other invertebrates transportation occurs by diffusion
All animals reproduce either asexually or sexually. Asexual by mitosis and sexual by meiosis and syngamy, embryos are present in all animals, they give birth to the young ones, or lay eggs. Regeneration is present in poriferous, cooperates, Platyheles All animals lack cell walls, no plastids in their cells but centrioles are present
9.2 Criteria for animal classification
Kingdom Animalia is divided into two subkingdoms Le, parano, and eumetazoa. (Table 1). The two subkingdoms are formed based on the presence or absence of cellular organization. The para zee (par) beside or animal) are an ancestral sub-kingdom of
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animals. They are simplest multicellular animals believed to be evolved from protozoans, their body is just a collection of cells that are not differentiated into t or organs, there is some division of labor among cells but are not strongly associated perform a specific collective function
The only surviving razors are sponges belonging to the phylum Perifera. Most asymmetrical animals, however, are radially symmetrical Sub kingdom cumetazoa includes animals, in which body cells are arranged in tissues, the tissues organized into organs, and organs into organ systems.
The cell tissues of neumes are arranged into layers, either diploblastic (two germinal layers or triploblastic (Three germinal layers) Germinal layers are present during the development of an embryo.
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