Centipede adult length ranges from 0.15 to 11.8 in (4-300 mm). The head has one pair of slender antennae, composed of 14 to more than 100 articles. Eyes are either faceted (Scuti-geromorpha), or composed of one ocellus or a cluster of ocelli on each side of the head (most Lithobiomorpha and all large Scolopendromorpha), or completely lacking eyes (all Geophi-lomorpha, many smaller Scolopendromorpha). The mouth-parts include a pair of mandibles and two pairs of maxillae. The first trunk legs are modified as mouthparts (maxillipedes) that become a functional part of the head. The maxillipedes contain a poison gland, with the venom injected through an opening near the end of the fang. The trunk has 15-191 pairs of legs, with one pair per segment, of which the last pair is usually the only one that is significantly modified: the last pair of legs has a sensory, grasping, or defensive function. The legs have six main segments, including coxa, trochanter, prefemur, femur, tibia, and a one- or two-part tarsus, and a terminal claw. Respiration is by tracheae, which are usually finely branched. The genital opening in both sexes is at the posterior end of the trunk.
As in other arthropods, the heart is dorsal and tubular, extending into the head as the aorta. The ventral nerve cord has paired ganglia in all leg-bearing segments. The brain is tripartite, as in insects. The gut is divided into an esophagus, midgut, and hindgut. The main excretory organs are a pair
of Malpighian tubules that originate at the junction of the midgut and hindgut. An elongate ovary or testes run through much of the trunk. In both sexes, paired accessory glands originate at the genital atrium, at the rear end of the body.
Segments are of uniform length along the trunk on the underside of all centipedes. In all orders except Geophilomor-pha, the tergal plates alternate between long and short along the trunk, except for between the seventh and eighth leg-bearing segment, where two long tergites occur in sequence. The tracheae open to spiracles that are confined to segments with long tergites, but are present on all trunk segments, except the last in Geophilomorpha. The number of leg pairs in centipedes totals to an odd number.
Color is highly variable. Most centipedes are drab, with the head and tergal plates yellow or brown (most Geophilo-morpha and Lithobiomorpha). Large Scolopendromorpha are often brightly colored, often with a dark band across each tergal plate; in this order, the head and legs may be a different color than the trunk tergites.
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