Invertebrates are animals without backbones. They have numerous possible body shapes and fall into many different animal families, including insects, jellyfish, and worms. Invertebrates are considered more primitive evolutionarily than vertebrate animals, and the variety between different kinds is much more extreme. Most experts agree that approximately 96% of all animals on the planet are invertebrates.
The invertebrate animals fall into eight different subtypes. Some of the more well-known types are the arthropods, nematodes, mollusks, and annelids. Arthropods are the insects, arachnids, and crustaceans, and they are the most numerous kind of invertebrate species. Mollusks are also very common, and they include snails and squids. Nematodes are round worms, and annelids are segmented worms like earthworms and leeches.
Invertebrates serve important purposes in terms of planetary ecology. For example, many crops are fertilized by invertebrates, and without them, much of humanity’s agricultural efforts could potentially be ruined. They are also an important food source for creatures all over the planet. Many mammals, including humans, consume large numbers of invertebrates, and if the invertebrate species population were to suffer, starvation would be a possibility for many species.
Some invertebrate species can also be harmful to people, and many of the world’s most dangerous parasites are members of the invertebrate family. Some of the more well-known invertebrate parasites include ticks, fleas, and leeches. There are also parasites like tapeworms that live within the body of their hosts, and these can potentially be even more dangerous than their external counterparts. Some parasites, like mosquitoes, can be especially damaging because they can potentially carry diseases.
Most kinds of invertebrate species go through a process called metamorphosis during their development. This is useful, because the animals can fill different ecological niches at different times in development, which allows for maximum exploitation of food opportunities. During each phase of its life, the animal undergoing metamorphosis will generally have a totally different lifestyle and survive in a different way. A common example of metamorphosis would be a caterpillar making a protective cocoon and turning into a butterfly.
Invertebrate species can vary greatly in size. Most of them are fairly small, like insects and mites. Others, like some squids and octopi, can be fairly large. The largest invertebrate in existence is the architeuthis, also known as the giant squid, which can potentially be 65 feet (20 meters) in length. Other invertebrates like the ciliated protozoan are too small to be seen with the human eye.