Animals, 'Animalia' or Metazoa are a main group of multicellular, animal-like nutrition, and eucentric organisms of the kingdom. After birth, as an animal grows, its body plan develops in a definite way, although some animals go through a process of metamorphosis later in life. Most animals are motile, that is, they can move independently and on their own. Most animals are also heterotrophs, that is, they depend on other animals for food. The maximum known animal phylum appeared in the fossil record as marine species during the Cambrian Explosion 542 million years ago.
Etymology of the word
The word 'animal' comes from the Latin word animale, neuter of animalis, and is derived from anima, meaning living breath or spirit. In common parlance, the term is used for non-human animals. The biological definition of the term includes all members of the Kingdom Animalia, including humans.
Animals have many special properties that set them apart from other living things. Animals are eukaryotic and multicellular, which differentiates them from bacteria and most protista. They are heterotrophs, usually digesting food in an internal chamber, a characteristic that distinguishes them from plants and algae.
Food and energy sources
Prey is a biological interaction in which a predator (a host that is hunting) obtains food from its prey (the organism that has been attacked). Another main category of consumption is carnivore, the consumption of dead organic matter. Sometimes it is difficult to differentiate between these two types of feeding behaviours, for example, a parasitic species preys on a host organism and then lays its eggs on it, so that their offspring obtain food from its decomposing organic matter. can do.
Organisms release energy. Human life is made up of those bodily activities that relate him to the environment. These bodily activities require a constant consumption of energy. In the absence of food or oxygen, the activities of the body come to an end. When the body needs more energy, it is met by food and oxygen. Therefore, respiration and assimilation are necessary for life. The substances from which our foods are made are capable of oxidation. This oxidation process produces heat. The process of oxidation in the body produces energy, which is available for the functioning of living beings.
Due to the huge diversity of animals, it is more economical for scientists to study a small number of selected species, in order to establish a relationship with their actions and conclusions on this subject, how animals work in general. Because it is easy to keep and hybridize them. This was facilitated by the highly reduced state of their genome.
History of classification
Aristotle divided the living world into plants and animals, and then Carolus Linnaeus (Coral von Linne) made the first hierarchical classification. Since then, biologists have been emphasizing evolutionary relationships, and therefore these groups have become somewhat restricted. For example, microscopic protozoa were originally thought to be animals because they move, but are now kept separate. In Linnaeus's original plan, animals were one of three kingdoms, divided into the classes Vermees, Insecta, Pisces, Amphibia, Aves, and Mammalia. Since then the last four classes are placed in a single phylum chordata, while many other forms have been split off.
The above list represents our current knowledge or understanding of the group, although there is some variation among different sources.