Depending on their body, we can divide animals into two groups: vertebrates and invertebrates. But... what are their differences? Let's see it! 

What are vertebrates?

Vertebrates are animals with a spinal column and an elaborate skeletal structure. They have some characteristics: 

1. All vertebrates have muscles and skeletons that help them to move around easily and perform complex moves.

2. All vertebrates also have an endoskeleton, which consists of the bones that are inside a body which gives them their shape and allows them to stand erect.

3. All vertebrates have skin covered with scales, fur, hair, or feathers.

VERTEBRATES ARE CLASSIFIED INTO FIVE GROUPS:

• FISHES: They are cold-blooded animals with streamlined body, gills to breathe and fins for movement. In most of the cases, the body is covered with scales to protect their body. Some examples are the goldfish, the seahorse or the shark. 

• AMPHIBIANS:  They are cold-blooded animals which can live both on land and in water. They breathe through both lungs and moist skin, and they reproduce only in water. The toad, the frog or the salamander are examples of amphibians. 

• REPTILES: They are cold -blooded animals which live on land and breathe with lungs. They have dry and scaly skin and they lay eggs. Some examples are snakes, turtles or crocodiles. 

• BIRDS: They are warm blooded animals with the body covered with feathers. Their forelimbs are wings, and they breathe through lungs. Their bones are hollow and they lay eggs. Pigeons, parrots and peacocks are examples of birds. 

• MAMALS: They are warm blooded animals which breathe through lungs. They give birth to babies and they have mammary glands to produce milk. Some examples are the dogs, the cats or the humans. 

What are invertebrates?

Invertebrates are animals without a spine. They have no vertebrae. Their characteristics are: 

1. They are multi-cellular and all the cells are assigned different tasks.

2. They have no cell walls.

3. They reproduce by two reproductive cells or gametes.

INVERTEBRATES ARE CLASSIFIED INTO EIGHT GROUPS:

• SPONGES: They live in salt water fixed to some object and their body is covered with pores through which their food enters. Some examples are the sycon and the spongilla. 

• CNIDARIANS: They live in the marine habitat and their body is like a tube with one opening called mouth. This mouth is surrounded by tentacles that help in capturing prey. They have a radially symmetrical body. Some examples are the jellyfish or the hydra. 

• FLATWORMS: They can be found in marine/fresh water. They have flat, ribbon shaped body that is bilaterally symmetrical, and it has a single opening. Most of them are parasites. The liver flucke is an example of flatworms. 

• ROUNDWORMS: They are found in fresh/marine water or on land, and they have a thread like, rounded body. They have an unsegmented and bilaterally symmetrical body, which has two openings, mouth and anus. Most of them are parasites and reproduce sexually by laying eggs. An example is the pinworm.

• SEGMENTED WORMS: They are found in marine and fresh water, and they have segmented bilaterally symmetrical body with a cavity. They have special organs of excretion known as Nephridia. Some examples are the earthworms or the leech. 

• ARTHROPODOUS: They have a segmented, bilaterally symmetrical body, divided into three parts - head, thorax and abdomen. It is covered by a tough outer covering called exoskeleton. They have jointed appendages. The honeybees, the ants or the spiders are examples of arthropodous. 

• MOLLUSKS: They have a soft unsegmented body with an external hard shell, like the squid, the snail or the octopus. 

• ECHINODERMS: They live in the marine environment and have spines all over the body, which is radially symmetrical. It has has two openings, mouth and anus, and they have tube like feet having suckers. The starfish or the urchins are examples of echinoderms. 

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