Kingdom Animalia: what it is, characteristics, classification and examples

The Animalia kingdom constitutes, together with the Planate , Fungi , Protista and Monera kingdoms, the five famous taxonomic kingdoms of biological evolution in which the different forms of life that exist (and have existed) on Earth are grouped. As its name suggests, each and every one of the different species of animals meet , grouped in a hierarchical system based on the homologous characters they share with each other. In this way, animals constitute a large, ancient and well-defined “branch” within the evolutionary tree of life, which originated about 600 million years ago.

Zoology is the part of biology in charge of the exhaustive study of the Animalia kingdom, having as some of its main objectives to discover all the animal species that exist, reconstruct their evolutionary relationships and reflect these relationships in the construction of a taxonomic system.

The different species that belong to the Animalia kingdom are distributed throughout each and every one of the various ecosystems of the biosphere, with zoogeography being the science in charge of this study of the geographical distribution of animals. Let’s see, next, more characteristics of the kingdom of animals :

• All animals are multicellular organisms , whose cells are characterized by the presence of a nucleus well limited by a membrane, that is, they are eukaryotic organisms.
• They are heterotrophic beings , that is, they depend on the consumption of other organisms to meet their nutritional needs. Thus, they have different strategies for capturing and processing the wide variety of foods they consume, as well as a regulation of the ingestion and digestion of said foods. Learn more about Heterotrophic Organisms: what they are, characteristics and examples with this other article.
• They have different locomotion systems that allow them to move and move, as well as the presence of integuments and other support and protection systems.
• The morphology and size of the animals is surprisingly complex and variable.
• A complex nervous system and sense organs characterize the vast majority of groups of animals. Made up of a network of neurons and different junction points between nerves, the process of synapses and nervous coordination confers on animals one of the most amazing capacities for interspecific relationships , that is, to relate to other living beings and the nature that surrounds them.
• They have an endocrine system in charge of the regulation of the numerous and diverse hormones that intervene both in the metabolism of animals, as well as in their behavior and social and reproductive relationships.
• Animals have circulatory systems to achieve a fast and efficient transport of nutrients and other dissolved substances that guarantee the correct functioning of their organs. These circulation systems transport different body fluids, such as blood, and are sometimes characterized by being open systems (as in arthropods) or closed systems (as in vertebrates).
• Gas exchange is carried out from the complex process of respiration , for which animals have various strategies and organs adapted to meet the respiratory needs of the body. The pulmonary respiratory system of mammals, the gill of fish and the tracheal of arthropods stand out. In other groups of animals, such as some amphibians, respiration is cutaneous, through the skin.

Thanks to the study of Phylogeny, zoologists make known the great diversity of animals that exist, taking into account their evolutionary origins, organization models and set of biological properties that relate or distinguish them from each other. For example, the presence or absence of bones makes it possible to classify animals into vertebrates or invertebrates.

The classification of the kingdom of animals is currently very complex, recognizing up to 32 different phyla. Within them, the best known and most abundant phyla, in order from least to greatest anatomical and functional complexity, are:

• Poriferous or sponges (9,000 species)
• Cnidarians (10,000 species)
• Flatworms or flatworms (20,000 species)
• Roundworms or nematodes (25,000 species)
• Annelids or ringworms (17,200 species)
• Mollusks (93,000 species)
• Arthropods or jointed legs (1,200,000 species)
• Echinoderms (7,000 species)
• Chordates (64,788 species)

Mammals, birds, reptiles, amphibians and fish belong to this last edge ; all of them characterized by the presence of a “dorsal cord” during their embryonic development, which is maintained throughout the life of many of the chordate species (in humans , Homo sapiens sapiens , said dorsal cord is called spine, vital for the correct locomotion and development of the nervous and cognitive abilities that characterize us as a species).

Let’s give some examples from the kingdom of animals , following the classification in the previous section, to learn more about the great diversity of species that fill every corner of the biosphere with life:

• Poriferous: violet tubular sponge ( Aplysina archeri ), freshwater sponge ( Spongilla alba ) and vitreous sponge ( Aphrocallistes vastus )
• Cnidarians: jellyfish (subphylum Medusozoa), anemones and corals (subphylum Anthozoa).
• Flatworms: planaria (genus Prostheceraeus), flukes or flukes (class Trematoda) and tapeworm (Taenia saginata).
• Nematodes: potato root nematode (genus Globodera ), American necator ( Necator americanus ) and pinworm ( Enterobius vermicularis ).
• Annelids: leeches (Haemadipsa class), earthworms (Oligochaeta subclass) and sea feather dusters (Sabellida class).
• Mollusks: clams (Veneroida family), mussels (Mytilidae family), octopuses (Octopoda order) and squid (Teuthida order).
• Arthropods: tarantulas (family Lycosidae), praying mantises (family Mantidae), centipedes (Class Chilopoda) and crabs (Crustaceans).
• Echinoderms: starfish (class Asteroidea) , sea urchins (class Echinoidea) and holothurians (class Holothuroidea).
• Chordates: white shark ( Carcharodon carcharias ), snow leopard ( Panthera uncia ), peregrine falcon ( Falco peregrinus ), Nile crocodile ( Crocodylus niloticus ), common salamander ( Salamandra salamandra ).