Kingdom Animalia: characteristics, classification and examples

The kingdom Animalia or Metazoa comprises all the animals that exist. Let's see what it looks like.

The kingdom Animalia, also known as Metazoois a large group of organisms that are the animals, among which we humans are found. The term animal comes from the Latin animalis, which means "that takes the air", "that has a soul".

Most of them can move and reproduce sexually, however there are some exceptions, which have contributed to the idea that some species, such as sponges and sea lilies, are considered plants.

We are going to see the characteristics that define this kingdom, with their particularities, and some of the groups that conform it.

Characteristics of the kingdom Animalia

Although the ways in which they feed, anatomy, reproductive behaviors and other aspects differ greatly, most animals have a number of characteristics in common:

1. multicellular

They are organisms composed of more than one cell. These cells are organized into specialized tissues, constituting organs and systems, which allow them to carry out differentiated functions. Thanks to this, animals have a nervous system and also muscles, which allow them to carry out different behaviors.

2. Heterotrophic nutrition

Unlike plants, which photosynthesize in order to generate their own food, animals depend on other organisms for their subsistence. depend on other organisms for their subsistence.. Basically, this type of nutrition involves transforming organic matter into the nutrients needed by the organism.

The source of food can be very varied depending on the species. There are herbivorous animals, such as cows, which feed exclusively on plants. Others, on the other hand, are carnivores, such as lions, feeding on other animals. If it feeds on both animals and plants, the animal is omnivorous.

There are other categories that refer to more specific types of feeding: nectarivores (flower nectar), insectivores (insects and other arthropods), xylophagous (wood)...

3. Aerobic metabolism

The vast majority of animals need oxygen in order to carry out their metabolism and maintain their basic functions.. One of the few exceptions to this is the case of loricifera, which can live in environments where there is no oxygen and survive.

4. Reproduction

In most cases, animals reproduce sexually. This implies that there is a differentiation into two sexes: males and females. The advantage of this type of reproduction is that it allows for genetic variability, however, it has the disadvantage that the process is very slow, since it is necessary to find a sexual partner, initiate courtship, fight for it if necessary and perform the sexual act, all of which requires energy.

There are some animals that reproduce asexually, such as sponges or sponges.such as sponges or worms, which can multiply by bipartition, that is, by breaking in two and creating a new individual from the original.

5. Sensory capacity

Because the organs can carry out different functions, animals have several types of senses. In addition to the five generally known senses (smell, taste, touch, vision and hearing), there are other senses with very specific evolutionary purposes.

For example, snakes have infrared sensors with which they identify the heat of their prey. Some insects, such as moths, can smell pheromones and locate a potential breeding partner several kilometers away. Sharks have electrical sensors and pick up electrical fields, locating prey and sensing how fast they are going or if they are camouflaging themselves.

6. Symmetry

Most organisms in the kingdom Animalia have a symmetrical anatomy, i.e., their body can be divided into two equal parts from one axis.. Depending on the type of symmetry, animals can be divided into bilateral symmetrical and non-bilateral symmetrical.

7. Locomotion

The representatives of the kingdom Animalia can move by themselves.and there are several ways in which they can do so. Some, such as starfish, have hundreds of tiny feet on their limbs that allow them to move along the seabed. Others, such as humans and other mammals, move by using their limbs, such as legs and fins.

Some animals, when they reach adulthood, stop moving. Examples are corals and anemones.

Classification and phyla

The kingdom Animalia comprises more than two million living speciesThese have been grouped into more than 30 phyla, categories that serve to classify all this biodiversity. Some of the best known are listed below:

1. Chordates

Their name comes from the fact that they have a dorsal cord, a dorsal neural tube or a tail at some point in their development. or tail at some point in their embryonic development. It is the third phylum with more described species, being mostly vertebrates (animals with internal skeleton), and more than half of them are fish.

Some groups of chordates are all vertebrates, such as mammals, spiny fishes, reptiles, amphibians and birds, as well as some marine species such as cephalochordates and hagfishes.

2. Arthropods

These are invertebrate animals with exoskeletons and articulated appendages.They are insects, arachnids, myriapods and crustaceans. It is the animal phylum with the most described species, representing 80% of the known animal species.

Thanks to their great adaptability, they come in multiple shapes and sizes, one of the largest arthropods in history being the extinct meganeura or giant dragonfly, which could reach 70 cm.

3. Porifera

This phylum includes sponges.which, contrary to what many people believe, are part of the kingdom Animalia. They are mostly marine and have the peculiarity that they are sessile (fixed to the ground) and have no real tissues, which is rare in the animal kingdom.

4. Mollusks

Mollusks include bivalves, squids, octopuses, snails and slugs. They are soft animals without an internal skeleton but may have shells for protection..

They are considered a phylum that has been able to adapt evolutionarily very well, being of marine origin but that managed to conquer terrestrial habitats. They have been found in places with extreme temperatures, such as polar and tropical waters.

5. Annelids

They are worms with rings, such as leeches and earthworms.. These rings are called metamers, which each have some repeated organs that, in case of division of the worm, allow the survival of new individuals.

They have both sexual and asexual reproduction. In the case of sexual reproduction, some species have two distinct sexes while others are hermaphrodites. Asexual reproduction occurs by excision, splitting in two.

Bibliographical references

• Hickman, C. P., Ober, W. C. & Garrison, C. W. (2006). Comprehensive principles of zoology, 13th edition, Madrid, Spain: McGraw-Hill-Interamericana.