Animals: What are they? Types and characteristics of animals

They walk on planet earth for a long time before men, there are hundreds of thousands of species on them, and although we think we know them, in reality they are still a mystery in their behavior, behaviors, biology and diversity, we talk about animals .

In this article we will try to answer questions such as: What is the definition of an animal? What does the word animal mean? What are animals? How many species of animals are there? How are they classified? What are their characteristics? What types of animals are there?

Table of Contents hide ]

  • 1What are animals?
  • 2Main characteristics of animals
  • 3Types of animals
    • 1Classification by its vertebral structure
      • 1.1Vertebrate Animals
        • 1.1.1Mammals
        • 1.1.2Fish
        • 1.1.3Birds
        • 1.1.4Reptiles
        • 1.1.5Amphibians
      • 1.2Invertebrate Animals
    • 2Classification according to their diet
      • 2.1Herbivorous Animals
      • 2.2Carnivorous Animals
      • 2.3Omnivorous Animals
    • 3Classification according to its form of reproduction
      • 3.1Ovoviviparous
      • 3.2Oviparous
      • 3.3Viviparous
    • 4Classification by livelihood
      • 4.1Terrestrial animals
      • 4.2Aquatic animals
      • 4.3Aerial animals
    • 5Classification according to natural habits
  • 4Vital functions of animals
    • 1Breathing
    • 2Food
    • 3Circulation
    • 4Playback
    • 5Excretion
    • 6Response
    • 7Movement
  • 530 Examples of Vertebrate and Invertebrate Animals
    • 115 Examples of Vertebrate Animals
    • 215 Examples of Invertebrate Animals
    • 3Human beings and animals

What are animals?

When we classify living things, we do it mainly into two types: plants and animals.

Animals are those living beings capable of moving, and that lack chlorophyll and cell walls, that is, they are very different from plants as we can see.

Men are included within the group of animals, although unlike these they have the ability to think.

Main characteristics of the animals

Here are the main or general characteristics of animals:

  • Its cellular organization can be eukaryotic or multicellular .
  • In the nutritional aspect , they are heterotrophic beings by ingestion, which is done in one way or another depending on the animal.
  • All animals have anaerobic metabolism , that is, they breathe oxygen and cannot live without it
  • Another common characteristic of all animals is that they reproduce sexually , generally finding a male and a female animal in the process.
  • They are also symmetrical beings , except for, for example, sponges. By having symmetry, they present a regular arrangement of the different parts or structures of their body along one or more body axes. Symmetry is either radial or bilateral.

With the exception of certain species, the vast majority of animals have muscles and a nervous system capable of sending and processing signals throughout the body.

In addition, all animals carry out these vital functions, such as: feeding, respiration, circulation, excretion, response, movement and reproduction.

Types of animals

Animals can be classified and differentiated in various ways. We can classify them according to their type of diet, their way of being born, whether or not they have a backbone or the environment in which they live and develop.

You can also establish a classification according to your natural habits, although it is not one of the most used, we will also develop it.

Classification by its vertebral structure

Animals may or may not have a backbone. Those animals that have a backbone are classified as Vertebrates, while those that do not have a backbone are Invertebrates.

Vertebrate animals

Vertebrate animals are those that have a spinal column and that have a complex bone structure. Its parts are composed and defined by limbs, trunk and head. A large percentage of them even have a tail.

Vertebrate animals have their bodies and skin covered, either by hair, in the case of most terrestrial animals, feathers in the case of birds, or scales in the case of fish and some species of reptiles. Most amphibians have bare skin.

It is estimated that there are currently more than 62,000 species of vertebrate animals. Vertebrate animals can be classified and divided into five main groups: mammals, fish, birds, reptiles, and amphibians.


Mammals make up a large part of land animals. What sets them apart from other vertebrates is that they are generally covered and protected by hair.

In most species, females have breasts that allow them to generate milk to breastfeed or feed their young, from when they are newborn until they are of an age where they can search and digest their food on their own.

A quality of all mammals is their jaw, since they have what is known as dental bone. It is also a characteristic of almost all mammalian species, including humans, to have bones in the inner part of the ear, called hammer, anvil and stapes.

A characteristic of mammals is what is known as thermal homeostasis. This characteristic of mammals allows them to regulate the temperature and flow of blood, with the aim of maintaining an average internal temperature in their body, without varying directly depending on the temperature of the environment.


Fish differ from vertebrate animals as they have underwater respiration mechanisms through gills, by which they absorb oxygen dissolved in the water.

They have scales covering their body and have fins instead of limbs, which allow them to move in the aquatic environment. Unlike mammals, fish regulate their internal temperature and that of their blood, depending on the temperature present in their environment, which is called ectothermy.


Birds are warm-blooded living beings that have internal bone structure with upper and lower extremities, as well as a spinal column.

They can jump and walk, although their lower limbs are not specially developed for this task, and they are most notable for their ability to fly thanks to their wings, although not all birds can use their wings to fly and some can only achieve great jumps with them (for example chickens).

In most species, their body is covered with feathers with different colors and textures, some even have designs with camouflage capacity as protection against predators. The way birds reproduce is through eggs and incubation.


Reptiles are vertebrate animals whose body is mainly covered with scales for protection. They have powerful limbs and a system of reproduction by shell eggs.

They have adapted to terrestrial life and have developed defense mechanisms, good lungs and camouflage, as well as a double circulatory blood system, in which a blood circuit circulates blood to the lungs specifically and another circuit to the rest of the body.

Reptiles have the ability to regulate their internal temperature by adapting to the external heat sources that are in their environment, that is, they are ectothermic, so to warm their body they lie in the sun for several hours, while to Cooling requires shelter in the shade or in hiding places.

Most reptiles are carnivores and have a simple digestive system for their food.


One of the characteristics of amphibians that is especially unique and striking is that while they are in their larval phase, they have a type of respiration similar to that of fish and can breathe underwater, while when they reach their adult life , develop terrestrial lung respiration.

Some amphibians have developed complex defense mechanisms to combat their predators. For example, many of them have poisonous glands in the skin, which can be detected due to its color, that the stronger or more striking it is, the more developed these glands are and the more powerful their poison.

This is what is called aposthematic staining or “warning” staining.

Invertebrate animals

Invertebrate animals, unlike vertebrates, are those that do not have a bone structure or backbone.

Many of these animals are small, and have shells or shells as a home and protection, since they turn out to be very vulnerable. As they are not organized with a bone structure, it is not possible to identify the parts of your body in this way.

Many species of invertebrate animals are protected by bony shells or shells, or by having an external structure called the exoskeleton.

They represent approximately 95% of all animal species on planet earth, and do not have the capacity for colonization or adaptation.

They have adapted to all livelihoods, in underwater environments and even in high altitude environments. They are very ancient species and of the most numerous forms of life present on the planet. Invertebrate living beings are made up of groups and classes that contain thousands of species, such as porifers, cnidarians, mollusks, annelids, echinoderms and arthropods.

Classification according to your diet

There are three primary ways of feeding in which we can differentiate and classify animals: Herbivores, Carnivores and Omnivores.

Herbivorous animals

They are those whose main food consists of plants, vegetables, herbs, fruits and derived mainly from plants and vegetation.

It is possible that some species of animals are more oriented to ingest mainly, or to prefer a certain food in particular, although for the most part, herbivores feed on a wide variety of leaves, fruits and plants of all species.

Within the classification of herbivorous animals, we have those called frugivores, which are those that feed mainly on fruit, and those that are called frolivorous, which feed especially on leaves. The diet of these animals is usually a bit variable throughout the year depending on the area and the seasons.

Although the main food source of herbivorous animals are vegetables and their derivatives, many of them also feed on sources of animal protein, such as milk in the case of mammals.

Carnivorous animals

Carnivorous animals are those that base their main diet on meat. They are the ones that make up the dominant part of the food chain.

Their daily nutritional intake is based on the consumption of meat in two ways: predation or carrion. In predation, animals stalk their prey in groups or individually and attack a common target. Scavengers mainly take advantage of the remains of prey left by predators once they finish consuming their desired food.

There are carnivores, as is the particular case of hyenas, that carry out group predatory hunting, and also take advantage of carrion, even stealing food from other predators.

There are also animals that have their particular classification, and they are those that are only responsible for the predation of certain animals or specific species, as is the case of ophiophagi, which are those animals that only feed on snakes.

Omnivorous animals

Omnivorous animals are those that feed on both vegetables and plants, as well as animals and insects. Your stomach is not specially designed to digest a particular food group. The human being, in a general way, is classified as Omnivore.

Classification according to its way of reproduction

We can classify animals according to their way of reproduction and birth in three ways: Ovoviviparous, Oviparous and Viviparous or Placental.


Animals with ovoviviparous reproduction are those that develop inside an egg, which in turn is inside the female’s uterus, and remains there until the embryo is fully developed.

At the time of delivery, the female gives birth, and the egg can hatch at that very moment or just being totally out of the uterus at that very moment.
Many reptiles or animals, such as sharks, exhibit this type of reproduction.


In the case of oviparous, contrary to the previous one, the animal lays the egg without the embryo being developed, and it develops over several days. The egg needs to be constantly heated by a process called “incubation.”


Viviparous are all those whose species develops a uterine cavity inside the female’s womb where the embryo will develop, receiving all the nutrients and oxygen for it.

The most developed viviparous are called placentals, which are those that give birth to the offspring once it is fully developed.

The least developed are the marsupials, which the females after giving birth, continue to connect to their young and continue to provide them with nutrients and protection, while they continue to develop in the marsupial bag or pouch. One of the clearest examples of this is the case of the kangaroo.

Classification by way of life

We can classify their animals according to their way of life or their natural habitat, to which they have adapted to survive, develop and reproduce. Three main means of life are established: terrestrial, aquatic and aerial.

Land animals

They are all those whose natural habitat is in the terrestrial environment, and live and develop on dry land. They find all the means necessary for their survival and are physiologically adapted for life in this environment. They breathe oxygen from the air through their lungs, and find their food in their terrestrial habitat.

Among land animals, we can find from mammals, to reptiles and amphibians, even birds that are not capable of flying, such as the ostrich or the hen, so it is a varied livelihood in species of all kinds.

Aquatic animals

Aquatic animals are classified as those that spend their entire life, or most of it, in water, this being their natural means of life.

Some animals, like most fish, have developed breathing systems that absorb dissolved oxygen in the water through gills, while others, such as dolphins, need to come to the surface to breathe and take oxygen from the air.

Among aquatic animals, we can classify fish, certain classes of mammals, birds and amphibians, and even reptiles, which spend most of their life in water, so it is also another very varied way of life in species of all.

Flying animals

Aerial animals are those that have the ability to fly and move through the air. They have a light bone structure, since most of their bones are hollow, well-developed pectoral muscles and an aerodynamic and low-weight body, which allows them to fly with great power and even great speed.

They have a horny beak, and have a digestive system that allows them to disintegrate and digest food, since they do not have teeth.

Each species has its own flight technique, in addition to the fact that some adapt to certain specific areas according to air conditions, and choose this medium for their development.

It is the environment in which the least number of variety of species are found, since it only includes birds identified with the aforementioned physiological capacities, some types of flying insects and a single mammal: the bat.

Classification according to natural habits

Although it is not an official way to classify them, we can easily recognize certain species of animals according to their natural habits.

Despite the fact that many species today have lost their primary naturalness at some point, or have been adapted in some way to change their habits, they are generally divided into three groups: wild, farm and domestic.

  • Wild Animals: are those that develop in free environments and in the natural habitat together with their species. It is possible to find wild animals in all regions, especially in some continents or areas such as the African Savannah or the Amazon Rainforest.
  • Farm animals : farm animals are those that have adapted to conditions of rural-wild life, although dependent on human beings, in order to take advantage of the resources that can be obtained from them.
  • Domestic animals or pets: pets are domestic animals and tend to have a very strong affective relationship with people in their familiar environment. In addition to providing companionship, many pets are critical for guidance, health, and safety purposes.

Vital functions of animals

Animals carry out a number of functions that they perform in their daily lives and that allow both their development as well as that of the species.

These vital functions can be carried out in different ways depending on the breed or type of animal, although all perform them, including humans, and are basic to life.

Specifically, these functions are: respiration, feeding, circulation, reproduction, excretion, response and movement.


Regardless of whether they are terrestrial or aquatic animals, all animals need respiration in order to survive. In respiration, oxygen is taken in and carbon dioxide is released. Some living beings have developed really complex and unique breathing mechanisms, which have allowed them to develop in different environments using the planet’s resources.


The vast majority of animals are heterotrophs, that is, they look for their food and eat it. The main food source varies according to the species and its classification.

Some are herbivores so their food source is mainly based on vegetables and plants, others are carnivores and eat mainly meat, and there are also omnivores, who eat both vegetables and meat.

There is also a type of filter feeding. It is more common in the case of aquatic species, for example sea sponges, which absorb amounts of water and filter their food.

In turn, animals can be related through so-called symbiotic relationships, in which two species coexist in a kind of association for the benefit of both or not.

In some cases, the relationship is from parasite to host, in which the parasite lives in or on the host and takes advantage of this to feed itself at the expense of the effort of others.

In other relationship cases, the benefit goes to both of you. An example of this occurs in the jungles of the African continent, where certain species of birds perch on the back of some large animals and benefit from them by obtaining their food easily.

The host, in this case, benefits from it since a large part of this food consists of parasites or insects that annoy and harm it, so both benefit from this symbiotic relationship.


Animals have a well-developed circulatory system in their organisms, which, like humans, is designed to transport nutrients, molecules and oxygen throughout their bodies.

There are some small organisms that do not have a complex circulation system, but rather have a system called diffusion, whose purpose is also to transport nutrients and oxygen through the system.


Reproduction in animals is mostly sexual between a male and a female member. This reproduction becomes the diversity and expansion of the species, contributing to its development and maintaining it.

Some animals, especially those that are invertebrates, can reproduce asexually. Asexual reproduction gives genetic origin to individuals identical to their parents, thus allowing a rapid increase in the number of individuals of the same species and its genetic preservation.


Animals have excretion systems that range from cells that pump water out of the body to organ systems that act as filters, such as the kidneys.

Most animals can expel their waste through systems made up of their digestive organs, or their organs have the ability to eliminate the main substances in the waste, and in this way help the animal’s system to maintain homeostasis.

Homeostasis is the ability to maintain a stable internal condition in the system through metabolism, compensating for changes through the regulated exchange of matter and energy with the outside.


Animals have specialized nerve cells which capture and generate stimuli to the changes that occur around them and in the environment. In most animals, these cells make up the nervous system. Cells called receptors are those that respond to external stimuli, such as light and sounds. Others are in charge of processing information and generate a response from the animal.

The organization and nervous systems of each animal change dramatically from species or classification to another.


Some kinds of animals are stationary, that is, they adapt to one environment and hardly change or migrate to another. For both mobile and stationary animals, their body is adapted with muscles and bones. Muscles and bones, both for mobile and non-mobile animals, form a system that allows and provides them both the mobility they need, as well as to fulfill their needs for obtaining food and daily actions.

30 Examples of Vertebrate and Invertebrate Animals

Here is a list of 30 animals, 15 of them vertebrates and another 15 invertebrates, with some of the characteristics of their species mentioned above.

15 Examples of Vertebrate Animals

Some examples of vertebrate animals are the following:

  • Dog
  • Cat
  • Monkey
  • Lion
  • Elephant
  • Panther
  • Giraffe
  • Tiger
  • Horse
  • Sheep
  • Shark
  • Canary
  • Parrot
  • Frog
  • Iguana

15 Examples of Invertebrate Animals

The following mentioned are invertebrate animals:

  • Octopus
  • Bee
  • Ant
  • Fly
  • jellyfish
  • Snail
  • Scorpion
  • Spider
  • Mosquito
  • Crab
  • Locust
  • Cricket
  • Butterfly
  • Praying mantis
  • Sea urchin

The human being and the animals

All animals, throughout their history and evolution, have adapted in the best possible way to the conditions of the planet to continue their development and survival of the species.

From the point of view regarding their relationship with humans, many animals play an important role, both from a social, as well as an economic and technological point of view, although sometimes, the human being in the desire to advance in a way economic, ends up seriously harming animal species.

Human beings have benefited from animals in points of health and technological advances, using them as an example or based on their structure for the development of advanced technologies throughout history.

Some notable cases of this have been the developments of airplanes based on birds, or that of submarines based on the structure of fish and sea creatures.

Animals are also a very important part of the culture of some countries or regions, being characterized by stories, legends, representations or even objects of religious veneration throughout the history of humanity.

Pets and domestic animals are an integral part as members of millions of families around the world, being faithful companions and friends of humans.

Pets provide fun and company to people, creating extremely strong bonds of affection and companionship in many cases.

In addition, there have also been studies that indicate that the company of pets can improve both physical and emotional health, and be indispensable companions for the elderly.

Domestic animals have also been used as a great help tool for different areas, for example, guide dogs, which care for and protect human beings with visual disabilities, or their inclusion in security forces, which have allowed criminals to be caught , drug or bomb detection, saving hundreds of people.

The development of industries, however, has meant the worst part for animals of all kinds. The textile industries have used animal skins for the manufacture of fabrics and other products, as well as indiscriminate hunting for the sale of hides or coveted animal products, such as horns in the case of rhinos or tusks in elephants, they have meant thousands of deaths, even putting countless species of wild animals in danger of extinction.

The reduction of forests, due to the obtaining of raw material or the advance of urbanization, has also meant the reduction of many areas of life and animal development, which have been forced to migrate to other points to find a new home, or They have died from these causes, unable to adapt.

In recent years, several world and governmental organizations have been created and united for the preservation and care of animals, as well as the preservation of their natural habitat.

It is time to generate a change in the world, as well as in the way of treating the living beings that inhabit our planet.

We must care for and protect them, as many are in danger of becoming extinct. For this reason, it is important to generate ecological and social awareness, so that we can protect and preserve the species of our land.

by Abdullah Sam
I’m a teacher, researcher and writer. I write about study subjects to improve the learning of college and university students. I write top Quality study notes Mostly, Tech, Games, Education, And Solutions/Tips and Tricks. I am a person who helps students to acquire knowledge, competence or virtue.

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