An arthropod is an invertebrateanimal having an exoskeleton (external skeleton), a segmented body, and jointed appendages. Arthropods are members of the phylumArthropoda (from Greekἄρθρονárthron, "joint", and πούςpous (gen.podos), i.e. "foot" or "leg", which together mean "jointed leg"), and include the insects, arachnids, and crustaceans. Arthropods are characterized by their jointed limbs and cuticles, which are mainly made of α-chitin; the cuticles of crustaceans are also biomineralized with calcium carbonate. The rigid cuticle inhibits growth, so arthropods replace it periodically by moulting. The arthropod body plan consists of repeated segments, each with a pair of appendages. Their versatility has enabled them to become the most species-rich members of all ecological guilds in most environments. They have over a million described species, making up more than 80% of all described living animal species, some of which, unlike most animals, are very successful in dry environments. They range in size from microscopic plankton up to forms a few meters long.
The Coleoptera/koʊliːˈɒptərə/order of insects is commonly called beetles. The word "coleoptera" is from the Greekκολεός, koleos, meaning "sheath"; and πτερόν, pteron, meaning "wing", thus "sheathed wing", because most beetles have two pairs of wings, the front pair, the "elytra", being hardened and thickened into a sheath-like, or shell-like, protection for the rear pair, and for the rear part of the beetle's body. The superficial consistency of most beetles' morphology, in particular their possession of elytra, has long suggested that the Coleoptera are monophyletic, but growing evidence indicates this is unjustified, there being arguments, for example, in favour of allocating the current suborderAdephaga their own order, or very likely even more than one.