Biology / Animal Kingdom

Animal Kingdom

The Animal Kingdom , Animalia or Metazoa is composed of heterotrophic organisms, that is, those that do not produce their own food.

This is one of the main characteristics of the group and what sets them apart from other living things, such as vegetables.

The beings that belong to the animal kingdom are eukaryotes and multicellular . They have locomotion ability and most of them reproduce sexually.

Animals are classified into several phyla, many of them being invertebrate animals (those without vertebrae).

Vertebrate animals with skull, vertebrae and backbone belong to the Corded Phylum.

Embryonic development determines important characteristics for its classification, all animals have the stage of blastula in its development.

Characteristics of the Animal Kingdom

  • Eukaryotes : cells with differentiated nucleus, ie, surrounded by membrane;
  • Heterotrophs by ingestion: need to ingest other living things, as they do not produce their own food;
  • Multicellular: body formed by many cells with specific functions;
  • Aerobic: Breathe the oxygen they get out of the air or water, depending on the environment in which they live;
  • Reproduction is sexual, that is, it involves the union of gametes. But some invertebrates do it asexually.
  • They do not have cellulose and chlorophyll (chlorophylls), a characteristic that differentiates them from vegetables;
  • They have tissues and organs, with the exception of the simplest phyla such as Porifers;
  • Presence of blastula: hollow sphere of cells with fluid inside. It is the second phase of cell segmentation in embryonic development following the formation of the zygote (morula-blastula-gastrula-neurula).
  • Presence of Celoma, an embryonic cavity present in all vertebrates, and the flatworms are pseudocellomate and the porifers do not have;
  • Most animals have bilateral symmetry: two symmetrical halves of the body. Radial symmetry (several longitudinal planes from the center of the body, for example: echinoderms) or absence of symmetry (sponges) can also occur.

Filos of the Animal Kingdom

The animal kingdom is divided into several phyla. The main ones are: porifers, cnidaria, flatworm, nematode or nematelminth, annelid, echinoderms, molluscs, arthropods and chordates.

Vertebrate Animals

The vertebrate animals belong to the Cordado Phylum (Chordata). The main feature of the group is the presence of the spinal cord and spine.

Chordate animals are divided into 5 classes: fish, amphibians, reptiles, birds and mammals.


Fish are animals with scaled bodies and gill breathing (they take oxygen out of the water). They do not control body temperature (pylothermic). Examples of fish are the goldfish, the stingray and the shark.


Amphibians are animals that depend on water in the larval phase (gill breathing) and undergo body metamorphosis in adulthood and acquire pulmonary respiration, such as frogs, frogs, tree frogs and salamanders. They are still petilothermal animals.


Reptiles are animals that have pulmonary respiration and are covered with scales or carapace. They can live in water or on land and are pecyrothermic. Examples are turtles, alligators and lizards.


Birds are feather-covered animals that have pulmonary respiration and control body temperature (homeotherms). Examples of birds are chicken, ostrich, rhea, penguin, parrot and hummingbird.


Mammals have hair, are homeothermic and have pulmonary respiration. One of the main characteristics of the group is the fact that the females feed the pups through the mammary glands.

Examples of mammalian animals are humans, cats, dogs and bats.

Invertebrate animals

Invertebrate animals are represented by numerous phyla with very different characteristics, but all are multicellular and have no cell wall .

There are eight phyla of invertebrate animals, namely: porifers, cnidaria, flatworms, nematelmints, mollusks, annelids, echinoderms and arthropods.


Porifers are primitive freshwater or saltwater animals. They are organisms that have no organs and no ability to move and reproduction can be sexual or asexual. Examples: sponges.


Cnidaria live in fresh or salt water and some of them have locomotion capacity while others are sessile.

One feature that makes them peculiar is the presence of a specific cell type, the cnidocytes. Some examples of cnidaria are jellyfish, corals, sea anemones, hydras and caravels.


The flatworms have a flat body and can be free-living or parasitic. Examples are tapeworms, loners, schistosomes and planarians.


Nematodes or nematodes have a cylindrical body and can be free-living or parasitic to humans and plants. Examples are roundworms, oxyureas and other worms.


The annelids have a segmented body composed of rings. They live in moist habitats on land and in fresh or salt water. Examples are earthworms, polychaetes and leeches.


The echinoderms are marine animals with presence of calcareous exoskeleton and hydrovascular system. Their body has pentarradial symmetry, that is, with 5 equal sides. Examples are sea cucumbers, starfish and sea urchins.


Mollusks are soft-bodied animals with shells, which may be internal (squid and octopus) or external (snails, mussels). They inhabit fresh or saltwater environments and wetlands.

Examples of mollusks include mussels, octopuses, squids, slugs, oysters and snails.


Arthropods comprise a very diverse phylum. They are characterized by segmented body and presence of chitin exoskeleton.

The main arthropods are:

  • Insects : butterflies, bees, cockroaches, flies;
  • Arachnids : spiders, mites, scorpions, ticks;
  • Myriapods : centipede, centipedes, gongols;
  • Crustaceans : lobsters, crabs, crabs, shrimps.