Living beings that, due to their characteristics, are included within the Animalia kingdom, are called animals. These creatures can move on their own, need the oxygen they breathe to survive, and reproduce sexually.
According to DigoPaul, invertebrate, on the other hand, is the adjective that identifies beings that do not have vertebrae or, therefore, a vertebral column. The vertebrae are a class of bones that have articulation between them and that make up the mentioned column.
It is clear, after reviewing these definitions, that invertebrate animals are those species of the Animalia kingdom that do not have the bones known as vertebrae. The set of invertebrate animals can also be defined by opposition and includes beings that are not within the group of vertebrate animals (which, obviously, do have vertebrae).
Jean-Baptiste Lamarck, a biologist from France who was born in 1744 and died in 1829, is noted as the pioneer in detecting and grouping vertebrateless animals within the invertebrate group
Invertebrate animals can exhibit very diverse characteristics. In fact, some live under water, others on the surface, and many even have the ability to fly.
Spiders, octopuses, earthworms, mosquitoes, shrimp, sponges, worms, leeches, and squids are some of the thousands of invertebrate animals that can be found on Earth.
As there is no backbone, no invertebrate animal has a central nervous system. These animals, however, have other kinds of nervous systems that allow them to interact with the environment and respond to stimuli.