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The most successful of the animals
The class Insecta is composed entirely of insects and is the largest group in the animal kingdom, with 29 orders and 800 000 known species. It is estimated that there may be up to 50 000 000 species of insects on Earth, most of which have not yet been discovered. Insects are in the phylum Arthropoda along with Malacostraca (crabs), Diplopoda (millipedes), Chilopoda (centipedes), and Arachnida (spiders, ticks). Insects are in the subphylum Tracheata because they breathe through a trachaea. All insects have a general appearance: a hard outer covering (exoskeleton) that is non-living and must be shed periodically; one pair of antannae (sometimes a second, smaller pair around the mouth); mouth parts perfected for licking, piercing, crushing, or sucking; 6 legs (3 pairs) all found on the thorax; and three body sections known as the head, the thorax, and the abdomen. Most insects have one or two pairs of wings.
Insects are the most successful forms of life on this planet. They are typically very small, the largest being about the size of a human hand. They locomote in a variety of ways, including swimming, jumping, gliding, flying, skating, clinging, floating, crawling, walking, running, and/or drifting. Class Insecta is one of the most diverse groups of animals on this planet. The 29 orders are:
(small, wingless insects)