Invertebrates, alone, represent 95% of all animals on earth. The main characteristic, common to all its elements, is the absence of a vertebral column. They occupy almost every habitat on the planet (aerial, land and aquatic).
The largest group within the invertebrates is the Class Insecta, i.e., the insects (200 million insects per human being!). Within the invertabrates we can also find arachnids (spiders, dust mites,etc), mollusks (clams, octopuses, etc), crustaceans (crabs, lobsters, etc) and many others.