Macroinvertebrate

macroinvertebrate, any animal lacking a backbone and large enough to see without the aid of a microscope. Macroinvertebrates are exothermic (or cold-blooded) and may be aquatic or terrestrial, the aquatic organisms often being larval or nymphal forms of otherwise terrestrial species. They can differ greatly in physical appearance, with some, such as crayfish, having an exoskeleton and others, such as snails, possessing a shell. Still others, such as leeches, have soft flesh with no support or protective structure. Today a wide variety of macroinvertebrates are known, and many are readily identified in nature. They include annelids (segmented worms), mollusks, arthropods, arachnids, crustaceans, odonates (mayflies, dragonflies, and damselflies), stoneflies, true bugs, beetles, caddisflies, and true flies.

One of the first biologists to study macroinvertebrates was Dutch naturalist Jan Swammerdam, who in 1675 described anatomical and biological features of the mayfly Palingenia longicauda. About a century later, macroinvertebrate species were named and classified en masse by Danish entomologist Johann Christian Fabricius.