The phylum Arthropoda (from Greek, arthron = joint + pods = feet) is the most numerous of the present earth. It contains about 1,000,000 known species, which is at least four times the total of all other animal groups gathered.
In addition, they have good adaptation to different environments, advantages in competition with other species, exceptional reproductive capacity, efficiency in performing their functions, resistance to toxic substances and perfect social organization, such as bees, ants and termites.
Arthropods have a segmented body (metamerized body), articulated appendages (paws, antennas and palps, etc.) and body covered with exoskeleton formed by a resistant and impermeable substance called chitin. Chitin is a polysaccharide nitrogenous polymer impregnated with wax layers.
In some, the exoskeleton is reinforced by the deposition of calcium carbonate (limestone). The skeleton covers the whole body, except the joints, forming, in the body segments, true plates.
Growing up, arthropods must abandon the old, small skeleton and make a larger one. This phenomenon is called mute or ecdise and occurs several times until growth ceases in adulthood. The carapaces left during the seedlings are the exuberant (from Latin exuviae, "dropped dresses").
Arthropods, however, have not only articulated paws, but all their ends and ends, such as antennas and mouthpieces. Your lower limbs are formed by parts that articulate, that is, that move relative to each other: your feet articulate with your legs, which also articulate with your thighs, which also articulate with the hip bones. .
Arthropods are usually classified by taking into account body divisions, the number of paws and the existence or otherwise of antennae and other appendages (pedipalps and chelicerae, for example). Taking these elements and the evolutionary approach into account, the representatives of the phylum Arthropoda would be grouped into five subphyls, one of which is now extinct, and some major classes, as we shall see below.