Insects (from
Latin , a
calque of
Greek [], "cut into sections") are a
class of
invertebrates within the
arthropod phylum that have a
chitinous exoskeleton, a three-part body (
head,
thorax and
abdomen), three pairs of jointed
legs,
compound eyes and one pair of
antennae. They are among the most diverse groups of
animals on the planet, including more than a million described
species and representing more than half of all known living
organisms. The number of
extant species is estimated at between six and ten million, and potentially represent over 90% of the differing animal life forms on Earth. Insects may be found in nearly all
environments, although only a small number of species reside in the oceans, a habitat dominated by another arthropod group,
crustaceans.
