Centipede crawling on my ceiling photo

Centipedes have elongated dorsal-ventrally flattened bodies, and comprise two segmented tagmata; a head and trunk, which bear different Hox gene expression. Each segment bears a single pair of legs and has a dorsal plate (tergite) and a ventral plate (sternite). Laterally each segment has a soft less sclerotized region known as the pleural membrane. This is where the spiracles for gas exchange are located in all orders except for the Scutigeromorpha (where they are located mid dorsally). The legs are segmented and segments are named proximal to distal: coxa, trachanter, prefemur, femur, tibia, and tarsus. Each leg terminates in a claw.

At the anterior end of the centipede is the head. Dorsally the head consists of a cephalic plate which is distinct in appearance from the tergites. Laterally on the head some centipedes have eyes. The order Geophilomorpha is blind. Scutigeromorphs have compound eyes and the other orders have no eyes or simple ocelli ranging from one pair to many. The ventral view of the head reveals the centipede's most prominent characteristic, its poison claws or forcipules. There are also three pairs of mouthparts all derived from the modification of appendages. There is a mandible with a first maxillae ventral to it and a second maxillae ventral to the first. These mouthparts are used for both feeding and grooming. At the anterior of the head there is a pair of antennae which vary in length and number of segments (except for the Geophilomorpha where the number of segments is fixed at 14).

The posterior end of a centipede has a conspicuous pair of legs named the ultimate or anal legs. These legs are not used for walking and are usually morphologically distinct from other pairs. Instead, they are used for defense and mating and so they often are morphologically distinct between the sexes. Ultimate legs can be inflated, excessively spined, and or morphologically complex with crests and furrows. The sexual organs are also located on the posterior end of the centipede. Sexual organs are externally visible in Scutigeromorpha and Lithobiomorpha, and some Geophilomorpha whereby males and females are easily distinguished. Scolopendromorpha do not have externally visible sexual organs, which makes sexing difficult. Scolopendromorph females may be larger or wider than males. Precise determination of sex can be accomplished upon dissection or by gently applying pressure and warm water to the genital sternite of a specimen to cause the sexual organs to emerge externally.

It is also notable that centipedes have distinct sensory structures. The Tomosvary organ in Lithobiomorphs and Scutigeromorphs is located just anterior to the position of the eyes. The organ appears externally as an ellipse and its function is largely unknown. It has been suggested that it is a pressure, light, or humidity sensor. There is some evidence that it functions as a pressure sensor to detect sounds . There are mechanoreceptors in the form of spines or hairs covering the legs and antennae. Lithobiomorphs have coxal pores on the ventral surface of the coxae of legs 12-15 in adults. These pores are present in pore fields consisting of 3-4 rows of pores. They are suspected to function in both osmoregulation and pheromone release. Pore fields are found on some Geophilomorph and Scolopendromorph species on various sternites and on the ultimate coxae. It is not certain if their function is similar across the orders.