part of the ecdysozoa group.
Arthropods are segmented invertebrates with jointed appendages and exoskeletons and include the following lineages:
Crustaceans (crabs, lobsters, shrimp, barnacles, roly- poly/pillbugs),
Chelicerates (horseshoe crab, scorpions, spiders, ticks, mites, etc.)
Myriapods (millipedes, centipedes)
Hexapods (insects)
also Trilobites (extinct)
Arthropoda includes two thirds of all described species of animals; Crustaceans and, especially, Insects are huge subgroups
Found in nearly all Earth habitats (Crustaceans especially in saltwater and freshwater habitats, Insects in terrestrial and freshwater habitats)
•Body covered by an external skeleton (exoskeleton) composed of the polysaccharide chitin (same as fungal cell walls!), infused with calcium
Insects (Hexapoda): A subgroup of Arthropoda that contains over half of all described animal species!
Most orders of insects go through successive nymph stages that more or less look like smaller versions of the adult (sometimes without wings in winged species)
However, the four most diverse orders of insects (beetles, moths & butterflies, flies, ants & wasps) go through a distinct complete metamorphosis from juvenile to adult stages. Early stages are for feeding (caterpillars, grubs, maggots), pupal stage is a protective outer skin while the insect undergoes drastic morphological changes, adult stage is primarily for reproduction- no further growth. Any feeding by adult stages, if they feed at all, is strictly for maintaining energy for reproductive activities