Hexapods Are a Diverse Group of Six-Legged Arthropods

Hexapods are a group of arthropods that include more than one million described, species, most of which are insects, but a handful of which belong to the lesser-known group Entognatha. In terms of the sheer number of species, no other family of animals comes close to the hexapods; these six-legged arthropods are, in fact, over twice as diverse as all other vertebrate and invertebrate animals combined. Most hexapods are terrestrial animals, but there are some exceptions to this rule. Some species live in aquatic freshwater habitats such as lakes, wetlands, and rivers, while others inhabit coastal marine waters. Hexapods Avoid Sub-Tidal Marine Areas The only habitats that hexapods avoid are sub-tidal marine areas, such as oceans and shallow seas. The success of hexapods in colonizing land can be attributed to their body plan (especially the strong cuticles covering their bodies that provide protection from predators, infection and water loss), as well as their flying skills. Another successful attribute of hexapods is their  holometabolous development, a mouthful of a term which means that juvenile and adult hexapods of the same species are very different in their ecological requirements, immature hexapods using different resources (including food sources and habitat features) than the adults of the same species. Hexapods Are Vital But Also Pose Many Threats Hexapods are vital to the communities in which they live; for example, early two-thirds of all flowering plant species rely on hexapods for pollination. Yet hexapods also pose many threats. These small arthropods can inflict vast crop damage and are known to spread numerous debilitating and fatal diseases in humans and other animals. The body of a hexapod is made up of three sections, a head, a thorax, and an abdomen. The head has a pair of compound  eyes, a pair of antennae, and numerous mouthparts (such as mandibles, labrum, maxilla, and labium). The Three Segments of Thorax The thorax consists of three segments, the prothorax, the mesothorax, and the metathorax. Each segment of the thorax has a pair of legs, making for six legs in all (the forelegs, the middle legs, and the hind legs). Most adult insects also possess two pairs of wings; the forewings are located on the mesothorax and the hind-wings are attached to the metathorax. Wingless Hexapods Although most adult hexapods have wings, some species are wingless throughout their life cycles or lose their wings after a certain period before adulthood. For example, parasitic insect orders such as lice and fleas no longer have wings (although their ancestors of millions of years ago did have wings). Other groups, such as the Entognatha and Zygentoma, are more primitive than classic insects; not even the ancestors of these animals had wings. Many hexapods have evolved alongside plants in a process known as coevolution. Pollination is one example of a coevolutionary adaptation between plants and pollinators in which both parties benefit. Classification Hexapods are classified within the following taxonomic hierarchy: Animals Invertebrates Arthropods Hexapods Hexapods are divided into the following basic groups: Insects (Insecta) - There are more than one million species of insects that have been identified, and scientists estimate that there may be many millions more species yet to be named. Insects have three pairs of legs, two pairs of wings and compound eyes.Springtails and their relatives (Entognatha) - The mouthparts of springtails, such as the two-pronged bristletails and the proturans (or coneheads), can be retracted within their heads. All entognaths lack wings. Edited on February 10, 2017, by Bob Strauss