Animals with no vertebral column (also known as a backbone or spine) are invertebrates. They come in all shapes and sizes; some invertebrates are microscopic, and others, like the giant squid, can be seen with the naked eye!
Instead of having a skeleton, many invertebrate animals have a thick shell known as an exoskeleton. Because these external skeletons don’t grow, many invertebrate animals have to shed their exoskeleton every so often!
Confusingly, some animals have both an internal and an external skeleton! For example, tortoises have a skeleton, and they also have a shell!
Are Invertebrates Animals?
An animal is a living organism that feeds off organic matter (i.e., other animals or plants). Typically, they have sense organs capable of responding to inputs like light, sound, or touch.
It is stated that 97% of all animals within the animal kingdom are invertebrates. Although over 1.25 million species have been described, most of which are insects, numerous more invertebrates have not been discovered living on Earth today.
In numbers, the invertebrate species could be in the 5, 10, or 30 million marks compared to only 60,000 vertebrates. A big reason why invertebrates are so successful is their reproduction rate. For example, insects like ants and bees lay eggs, which can develop without fertilization.
Invertebrate animals are also among the oldest animals in existence. For example, jellyfish have been around for over 500 million years! Sponges and some crustaceans (animals like crabs and lobsters) also enjoy similar longevity. Many of the world’s oldest animals live underwater. That’s because life on Earth started in the sea!
What are the five most common types of Invertebrates?
Within the vast number of Invertebrates, there are five main groups that many fall under. These include:
- Protozoans
Single-celled organisms such as paramecia, these invertebrates are free-living or can be parasitic. They feed on the matter, which can be other microorganisms, organic tissues, or debris.
- Annelids
Also known as ringed worms or segmented worms. They are a large phylum, and over 22,000 species of phylum exist, which includes earthworms and leeches. They are characterized by their body cavity, moveable bristles, and segmented body.
- Echinoderms
Marine invertebrates, including sea cucumbers, sea urchins, and starfish. They are a very diverse group and have an essential role ecologically for near-shore environments in deep seas.
- Molluscs
Soft-bodied invertebrates are usually enclosed in a calcium carbonate shell, with a soft mantle covering their body. Organisms within the mollusks type include Snails, octopuses, squid, clams, and scallops.
- Arthropods
Arthropods have five main characteristics; these types of invertebrates have Exoskeletons, where their bodies do not have internal bones. Second, they have segmented bodies, internally and externally. Third, arthropods have jointed appendages, bilateral symmetry, and an open circulatory system.
