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Characteristics Of Invertebrates

Group Characteristics of Invertebrates

Aside from having no backbones or spinal columns, characteristics of invertebrates differ from group to group. Squids and spiders, for example, are going to differ greatly, even though they are in the same main animal group.

The following article provides an overview of characteristics of invertebrates relating to their particular species and classifications. Please note that with over 30 phylum and 2 million different species of invertebrates, this article can only touch the very tip of the world of invertebrates.

General Characteristics of Invertebrates

Some invertebrate characteristics are shared across the board. For example, the one main characteristic that sets them apart from other animals is their lack of a backbone and spinal column. Also, despite the fact that they are multi-cellular, they in fact lack cell walls.

Due to their lack of complex skeletal system, invertebrates also tend to be smaller and slow moving in nature, but there are of course exceptions. Giant squids, for example, can grow to be upwards of 17 yards long, 2,200 pounds, and can reach speeds of 35 miles per hour.

Their lack of backbones and complex nervous systems make it very difficult for invertebrates to be adaptive to multiple environments as well. This is not to say that they all float in the ocean. Invertebrates can be found in myriad climate zones, ranging from dry deserts to swamplands. In fact, they essentially span the entire globe and even make up 98% of all the living creatures on this planet.


This group of invertebrates is comprised of approximately 1,150 parasitic worms. These worms are further characterized by their spined probiscus which pierces the intestinal walls of their hosts. They typically have very complex life cycles and can be found in several different types of host animals, particularly mammals, fish, birds, and even other invertebrates.


The Annelid group consists of 17,000 species of ringed worms, including the popular earthworm, leech, and ragworm. These creatures’ bodies have multiple segments, each containing replicate sets of organs. Sometimes, these segments are not visible from the outside of the body. Movement is accomplished generally through undulation, but some species have parapodia which allow them to move.


Arthropods make up 80% of all living creatures on the planet. Generalized characteristics include an exoskeleton and segmented bodies with jointed appendages. Consisting of over 1,100,000 different species, this phylum had to be further broken down into four subgroups: insects, crustaceans, spiders, and myriapods (centipedes and millipedes). These subgroups contain their own specific characteristics not shared by other invertebrates. Spiders, for example, have eight legs, whereas crustaceans have hard, protective shells and carapaces on their backs.


This phylum contains 9,000 species of jellyfish, sponges, sea anemones, and hydras. This group is found solely in water environments, due to their unique cellular structures that also allow them to capture their prey. Their bodies are predominantly comprised of a viscous, jelly-like substance that is held by two sandwiching layers of epithelium. All species of this group have a single digestive orifice and body cavity, since they ingest food differently.

See Related: Squid Reproduction


Mollusks are comprised of squids, snails, octopi, and bivalve species. It makes up approximately a quarter of all marine animals, and contains approximately 85,000 recognized species. While there are certainly a great deal of differences between snails and squids, this phylum boasts two main characteristics that all of its species share.

Mollusks have a mantle, which is a dorsal body wall that covers the internal organs, and a mantle cavity that houses many other organs and orifices. In addition to this, mollusks also have a very specialized nervous system.