Animals are multicellular, eukaryotic living beings. They have some distinct features like the ability to move, make sounds, collect food, and other activities.
They are the dominant living beings that consist of small animals like insects to intelligent, large animals like human beings.
They differ from plants in their ability to move from place to place and in their dependence on others for their food.
They have a brain that evolves further and can make decisions.
They can be classified into different types based on their food requirements, habitats, size, reproduction, body anatomy, etc.
Types of animals by evolution
- Sponges
- Coelenterates
- Worms
- Mollusks
- Arthropods
- Echinoderms
- Fishes
- Amphibians
- Reptiles
- Birds and
- Mammals (includes humans)
Based on other features like body physiology (respiration, reproduction, habitats)
Sponges
- These are multicellular organisms mostly found in marine waters.
- The cells do not form a tissue, so they have no organs.
- Each cell in the body survives on its own, but all the cells are intact. They have a column-shaped body.
Coelenterates (Cnidarians)
- These animals are more evolved than sponges.
- They have tube-like bodies and a mouth.
- They even have tentacles (appendages) to swim.
- They move from one place to another in search of food and shelter.
Ex: Hydra, which lives in freshwater.
Worms
- These are the biggest categories of living beings.
They are of three types
- Flatworms– Tapeworms
- Roundworms –Nematodes like roundworms, hookworms.
- Segmented worms– Annelids like earthworms, leeches.
- They exist as normal living organisms and also as parasites in other higher animals.
- They have a thread-like or tape-like body.
- They are slender and very long.
They are of different types, ex, Earthworms.
Arthropods (insects)
- These are animals that have joint legs. They are commonly called insects.
- They can be herbivorous or carnivorous.
- They are also parasites that cause diseases in other animals.
- Some of them are also parasites (lice).
- They are one of the biggest categories of animals available.
- They include house flies, mosquitoes, spiders, butterflies, etc.
Echinoderms
- This is a class of animals that includes starfish and mostly live in seas and oceans.
More examples include
- Sea Urchins
- Sea Cucumbers
- Sand dollars
Till echinoderms, we come across invertebrate animals.
From there on, we see the evolution of vertebrate animals.
Molluscs
These are soft-bodied animals that move on their belly.
They have a special protective shell or an ink-like protection mechanism to escape from predators.
Fishes
- These are the animals well-known to man.
- They are present in both freshwater and marine waters.
- They breathe with gills and swim with fins.
- They lay eggs to give birth to new ones.
Amphibians (Two-Beings = live in two places)
- As the name indicates, these animals can live on both land and in water.
- This group of animals includes especially the frogs.
- They are carnivores and also herbivores.
More examples include
- Salamanders
- Caecilians
Reptiles
These animals include
- Snakes,
- Lizards, and
- Crocodiles/ alligators.
- Turtles
- They are mostly carnivores except for tortoises.
- They live either on water or on land. Not on both.
👉 See the article on characteristics of reptiles and the List of reptiles.
Birds
- These are the animals that can fly.
- Birds can fly miles together due to their strong forelimbs.
- From these animals and mammals, we get the concept of warm-blooded animals.
- They have a constant body temperature irrespective of external climate conditions.
- They are carnivores but can eat even plant material.
- They lay eggs and give birth to young ones.
Mammals
- These animals are highly evolved among all.
- They give birth directly to young ones.
- They feed the babies with milk from their mammary glands.
Types of animals based on anatomy.
Based on the vertebral column
a. Vertebrates.
- These are the animals that have a vertebral column.
- This vertebral column houses the spinal cord and helps in connecting it with the brain.
- It also has cavities for the spinal nerves to connect with the whole body.
Examples include all
- mammals,
- birds, and
- reptiles.
b. Invertebrates.
- These animals do not have a vertebral column.
Due to this lack of a vertebral column, they have flexible body shapes—examples:
- Snails,
- Earthworms,
- Insects, etc.
Based on body temperature.
- All the animals have heat in their bodies due to their physiological activity.
- However, the animals differ in their regulation of body temperature as below.
Endotherms:
- These animals have a fixed body temperature despite changes in external temperatures.
- They do this by generating heat energy in their body as part of the metabolic process.
- They are also called homeotherms as their body temperature is constant.
- These animals have a homeostatic mechanism to keep their body temperature constant despite changing external temperatures.
- Failing to regulate this constant body temperature leads to their death.
The animals in this category include mammals and birds.
Ectotherms:
- Their body temperature varies with the external environment.
- Examples include amphibians (frogs), fish, and reptiles.
- Some of them are also called Poikilotherms.
- This means their body temperature fluctuates and has no adverse impact on their life. These include snakes and lizards.
Respiratory system
- Respiration is a process by which animals take in oxygen from the air and use it for energy generation by oxidative phosphorylation in the mitochondria.
However, due to their habitat and body size, animals have different organs and systems for respiration.
- Lungs
- Gills.
- Spiracle and Tracheae.
- Skin
Lungs:
- Larger animals like mammals, birds, and reptiles have lungs as their respiratory organs.
- They take in air into the lungs by inspiration and give out the air by expiration.
- By this process, the exchange of oxygen and carbon dioxide from the blood into the air takes place.
Gills:
- These are the organs meant for respiration in the water.
- Fish, mollusks, and Crustaceans have gills.
- Even the tadpoles of amphibians have gills before metamorphosis is complete.
Spiracle and Tracheae:
- These are the organs of respiration in insects.
- The spiracles open to the outside, and air enters the tracheae.
- From the tracheal tubes, the air enters directly into the tissues.
Skin and body surfaces:
- Skin is the organ that covers and protects the body of all animals. It is mostly impermeable.
- However, in a few animals, this skin helps in respiration. In animals like the eels, about 60% of oxygen is absorbed through the skin.
- In frogs, carbon dioxide is expelled from the body through the skin.
- In earthworms, the air exchange occurs on their surface through the capillaries.
Interestingly, animals like Jellyfish have no specialized respiratory organs. They take in gas from the water around them.
Reproduction
Animal propagates by reproduction, and there are some differences in this reproduction in animals like
- Based on the method of reproduction
- Based on the reproductive characteristics of animals.
Based on the process of reproduction
- Animals give birth to their young ones through either asexual or sexual reproduction.
- Asexual reproduction occurs by budding in small animals like the hydra, jellyfish.
- Sexual reproduction occurs by the fusion of male and female gametes.
- Most higher animals like fish, amphibians, reptiles, birds, and mammals follow this method.
This sexual reproduction also has some variations. Animals can be divided based on their reproductive characteristics, like
a. Hermaphrodites.
- These are the animals that have both male and female organs in the same body.
- They can produce male and female gametes. Examples include earthworms, banana slugs.
b. Dioecious (Male or female animals.)
- Here, the male and female organs are present in different individuals. So there are male animals and female animals.
- Most animals come under this category in terms of reproduction.
Based on the process as
Oviparous:
- These animals lay eggs after fertilization, which are attached to give birth to babies.
- Examples of oviparous animals include insects, fish, amphibians, reptiles, birds, and a few mammals like an echidna.
Viviparous:
- These are the animals that give direct birth to fully formed new animals.
- They grow the fertilized zygote in the uterus.
- They deliver fully formed babies, which are nourished till a certain age is attained.
This category of animals includes only mammals like cows, dogs, whales, lions, rats, etc.
References