An invertebrate is an organism that lacks a vertebral column or backbone, which is a defining characteristic of the animal kingdom. The term "invertebrate" encompasses a vast array of animals, including insects, spiders, worms, mollusks, crustaceans, and many others. Invertebrates make up the majority of animal species on Earth and exist in a wide range of habitats, from oceans and rivers to forests and deserts.
One of the key features of invertebrates is their exoskeleton, a tough outer covering that provides support and protection. In contrast to vertebrates, which have an internal skeleton made of bone or cartilage, invertebrates possess exoskeletons made of chitin, a complex polysaccharide. Furthermore, invertebrates may also have hard shells or tough cuticles, which enable them to survive in various environments.
In terms of physiology, invertebrates exhibit incredible diversity. They can vary greatly in size, ranging from microscopic organisms to giant squid or colossal insects. In addition, their methods of reproduction, feeding, and locomotion differ significantly among species. Some invertebrates, like worms, move through muscular contractions, while others have specialized appendages for swimming, crawling, or flying. Moreover, their diets can comprise a wide range of sources, such as plants, other animals, or even detritus.
In summary, an invertebrate is an animal lacking a vertebral column. It encompasses an extensive range of organisms, displaying diverse adaptations, sizes, habitats, and physiological functions.
