Invertebrate

Invertebrates are animals that don't have a vertebral column also known as backbone or spine. Invertebrates doesn't have skeleton ( also called as "endoskeleton") rather they have structures in the outside to protect them ( also known as "exoskeleton").
Below are the types of invertebrates:

1.) Protozoans- are single-celled Eukaryotes that usually associated with animals, they are either parasitic or free-living organisms. In history, they were regarded as "one-celled animals" because they often posses animal-like behaviors.

 
2.) Annelids- can be often found in wet environments.They are a phylum of invertebrate worms, they are segmented worms and most well known species are the leech and earthworms. Some species are parasitic, mutualistic, or both. They are characterized to have segments by transverse rings, body cavity, and movable bristles.

 

3.) Echinoderms- are one of the most diverse groups of marine invertebrate and play important ecological roles from the near-shore to the deep sea. Echinoderms cannot be found in land or fresh waters, they are radially symmetrical animals that can only be found in the sea. In addition, echinoderms can undergo complete regeneration from a single limb. Well known species are, starfish, sea cucumber, sea urchins, and sand dollars.
 
4.) Mollusks- are soft bodied invertebrates, usually wholly or partly closed in a calcium carbonate shell secreted by a soft mantle covering the body. They are one of the most diverse group of animals in the world.
 
5.) Arthropods- are one of the most successful groups of animals in the world, they have conquered the land, air, , and sea. They have jointed legs, segmented bodies, and chitinous exoskeleton. They are one of the most diverse animal in the world.
  

Next time we will discuss each major habitats of animals namely the forest, sea, and air.