Centipede

Centipedes (from Latin prefix centi-, "hundred", and Greek ποδός podos, "foot") are arthropods belonging to the class Chilopoda and the Subphylum Myriapoda. They are elongated metameric animals with one pair of legs per body segment. A key trait uniting this group is a pair of poison claws or forcipules formed from a modified first appendage. This also means that centipedes are an exclusively predatory taxa, which is uncommon.

Centipedes normally have a drab coloration combining shades of brown and red. and subterranean species may lack pigmentation and many tropical Scolopendromorphs have bright aposematic colors. Size can range from a few millimeters in the smaller Lithobiomorphs and Geophilomorphs to about a foot in the largest Scolopendromorphs.

Worldwide there are estimated to be 8,000 species. Currently there are about 3,000 described species. Geographically, centipedes have a wide range, which reaches beyond the Arctic Circle. Centipedes are found in an array of terrestrial habitats from tropical rainforests to deserts. Within these habitats centipedes require a moist micro-habitat due to their rapid rates of water loss. Accordingly, they are found in soil and leaf litter, under stones and deadwood, and inside logs. In addition, centipedes are among the largest terrestrial invertebrate predators and often they contribute a significant proportion to invertebrate predatory biomass in terrestrial ecosystems.

Anatomy
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 scelerotized region known as the plueral 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 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 similair across the orders.

Hazards to humans
Some species of centipedes can be hazardous to humans because of their poisonous bites. Although a bite to an adult human may only be painful, to those with allergies that are similar to that of bee stings and small children are at greater risk.

Evolution
Internal phylogeny of the Chilopoda. The upper three groups form the paraphyletic Anamorpha.

Centipedes have a fossil record dating back 420 million years to the late Silurian. They belong to the subphylum Myriapoda which includes Diplopoda, Symphyla, and Pauropoda. The oldest known fossil land animal is a Myriapod. Being one of the earliest terrestrial animals, centipedes were one of the first to fill a fundamental niche as ground level generalist predators in detrital food webs. Today centipedes are abundant and exist in many harsh habitats.

Within the myriapods, centipedes are believed to be the first of the extant classes to branch from a common ancestor. There are five orders of centipede: Craterostigmomorpha, Geophilomorpha, Lithobiomorpha, Scolopendromorpha, and Scutigeromorpha. These orders are united into the clade Chilopoda by the following synapomorphies: 1) first post-cephalic appendage modified to poison claws. 2) embryonic cuticle on second maxilliped has egg tooth. 3) the trochanter-prefemur joint is fixed. 4) a spiral ridge on the nucleus of spermatazoan. Chilopoda is then split into two clades: the Notostigmomorpha including the Scutigeromorpha and the Pluerostigmomorpha including the other four orders. The main difference is that the Notostigmomorpha have their spiracles located mid-dorsally. It was previously believed that Chilopoda was split into Anamorpha including the Lithobiomorpha and the Scutigeromorpha, and Epimorpha including the Geophilomorpha and Scolopendromorpha based on developmental modes, with the relationship of Craterostigmomorpha being uncertain. Recent phylogenetic analyses using combined molecular and morphological characters supports the previous phylogeny. The Epimorpha group still exists as monophyletic within the Pleurostigmomorpha, but the Anamorpha group is paraphyletic.

Geophilomorph centipedes are used to argue for the developmental constraint of evolution, because they have variable segment numbers within species, yet (as with all centipedes ) they always have an odd number of pairs of legs.

Life history
Centipede mating does not involve copulation. Males deposit a spermatophore for the female to take up. In one clade, this spermatophore is deposited in a web, and the male undertakes a courtship dance to encourage the female to engulf his sperm. In other cases, the males just leave them for the females to find. In temperate areas egg laying occurs in spring and summer but in subtropical and tropical areas there appears to be little seasonality to centipede breeding. It is also notable that there are a few known species of parthenogenetic centipedes. The Lithobiomorpha, and Scutigeromorpha lay their eggs singly in holes in the soil, the female fills the hole in on the egg and leaves it. Number of eggs laid ranges from about 10 to 50. Time of development of the embryo to hatching is highly variable and may take from one to a few months. Time of development to reproductive period is highly variable within and among species. For example, it can take 3 years for S. coleoptera to achieve adulthood, whereas under the right conditions Lithiobiomorph species may reach a reproductive period in 1 year. In addition, centipedes are relatively long-lived when compared to their insect cousins, for example: the European Lithobius forficatus can live for 5 or 6 years. The combination of a small number of eggs laid, long gestation period, and long time of development to reproduction has led authors to label Lithobiomorph centipedes as K-selected.

Females of Geophilomorpha and Scolopendromorpha show far more parental care, the eggs 15 to 60 in number are laid in a nest in the soil or in rotten wood, the female stays with the eggs, guarding and licking them to protect them from fungi. The female in some species stays with the young after they have hatched, guarding them until they are ready to leave. If disturbed the females tend to either abandon the eggs or young or to eat them; abandoned eggs tend to fall prey to fungi rapidly. Some species of Scolopendromorpha are matriphagic, meaning that the offspring eat their mother.

Little is known of the life history of Craterostigmomorpha.

Anamorphy vs. epimorphy
Centipedes acquire their legs at different points in their development. In the primitive condition, exhibited by the Lithobiomorpha, Scutigeromorpha and Craterostigmomorpha, development is anamorphic. That is to say, more pairs of legs are grown between moults; for example, Scutigera coleoptera, the American house centipede, hatches with only 4 pairs of legs and in successive moults has 5, 7, 9, 11, 15, 15, 15 and 15 before becoming a sexually mature adult. Life stages with fewer than 15 pairs of legs are called larval stadia (~5 stages). After the full complement of legs is achieved, the now post-larval stadia (~5 stages) develop gonopods, sensory pores, more antennal segments, and more ocelli. All mature apomorphic centipedes have 15 leg-bearing segments.

The Craterostigmomorpha only have one phase of anamorphis, with embryos having 12 pairs, and moultees 15.

The clade Epimorpha, consisting of orders Geophilomorpha and Scolopendromorpha, derived epimorphy. Here, all pairs of legs are developed in the embryonic stages, offspring do not develop more legs between moults. Interestingly, it is this clade that contains the longest centipedes; the maximum number of thoratic segments may also very intra-specifically, often on a geographical basis; in most cases, females bear more legs than males. The number of leg-bearing pairs varies widely, from 15 to 191 -- but the developmental mode of their creation means that they are always added in pairs - hence the total number present is always odd.

Ecology
Centipedes are an exclusively predatory taxa. They are known as generalist predators which means that they have adapted to eat a variety of different available prey items. Centipedes are also known to be nocturnal. Studies on centipede activity rhythms confirm this, although there are a few observations of centipedes active during the day and one species Strigamia chinophila that is diurnal. What centipedes actually eat is not well known because of their cryptic lifestyle and thorough mastication of food. Laboratory feeding trials support that they will feed as generalists, taking most anything that is soft-bodied and in a reasonable size range. It has been suggested that earthworms provide the bulk of diets for Geophilomorphs, since geophilomorphs burrow through the soil and earthworm bodies would be easily pierced by their poison claws. Observations suggest that Geophilomorphs cannot subdue earthworms larger than themselves, and so smaller earthworms may be a substantial proportion of their diet. Scolopendromorphs, given their size, are able to feed on vertebrates as well as invertebrates. They have been observed eating reptiles, amphibians, small mammals, bats and birds. Collembola may provide a large proportion of Lithiobiomorph diet. Little is known about Scutigeromorph or Craterostigmomorph diets. All centipedes are potential intraguild predators. Centipedes and spiders may frequently prey on one another Video.

Centipedes are eaten by a great many vetebrates and invetebrates, and form the staple diet of some. The African ant Amblyopone pluto feeds solely on Geophilomorphs and the South African Cape Black-headed snake Aparallactus capensis mainly feeds on centipedes.

Centipedes are found in moist microhabitats. Water relations are an important aspect of their ecology, since they lose water rapidly in dry conditions. Water loss is a result of centipedes lacking a waxy covering of their exoskeleton and excreting waste nitrogen as ammonia, which requires extra water. Centipedes deal with water loss through a variety of adaptations. Geophilomorphs lose water less rapidly than Lithobiomorps even though they have a greater surface area to volume ratio. This may be explained by the fact that Geophilomorphs have a more heavily sclerotized pleural membrane. Spiracle shape, size and ability to constrict also have an influence on rate of water loss. In addition, it has been suggested that number and size of coxal pores may be variables affecting centipede water balance.

Centipedes live in many different habitat types; forest, savannah, prairie, and desert to name a few. Some Geophilomorphs are adapted to littoral habitats, where they feed on barnacles. Species of all orders excluding Craterostigmomorpha have adapted to caves. Centipede densities have been recorded as high as 600/m2 and biomass as high as 500 mg/m2 wet weight. Small Geophilomorphs attain highest densities, followed by small Lithobiomorphs. Large Lithobiomorphs attain densities of 20/m2. One study of Scolopendromorphs records Scolopendra morsitans in a Nigerian savannah at a density of 0.16/m2 and a biomass of 140 mg/m2 wet weight.

Largest centipede
Scolopendra gigantea, also known as the Amazonian giant centipede, is the largest existing species of centipede in the world, reaching over 30 cm (12 inches) in length. It is known to eat bats, catching them in midflight, as well as rodents and spiders. The prehistoric Euphoberia was the largest known centipede, growing up to one metre (39 inches) in length.

There are rumors that state that the Galápagos Islands giant centipede (Scolopendra galapagoensis) can reach sizes of up to 60 cm (over 25 in), although these rumours may result from the rarity of the particular centipede. Captive Galapagos centipedes don't often exceed 20 cm (8 inches) in body length.



Orders and families
The orders of centipedes are considered below, from primitive to derived.

Scutigeromorpha
The Scutigeromorpha are anamorphic, reaching 15 leg-bearing segments in length. They are very fast creatures, and able to withstand falling at great speed: they reach up to 15 body-lengths per second when dropped, surviving the fall.

They are the only centipede group to retain their original compound eyes, with which a crystalline layer analogous to that seen in chelicerates and insects can be observed. They also bear long and multisegmented antennae. Adaptions to a burrowing lifestyle has led to the degeneration of compound eyes in other orders. This feature is of great use in phylogenetic anaylsis.

The group is the sole representative of the Notostigmomorpha, defined by having single spiracle openings on the back of their ventral plates. The more derived groups bear a plurality of spiracular openings on their sides, and are termed the Pleurostigmomorpha. Some even have 7 unpaired spiracles that can be found along the middorsal line and closer to their posterior section of tergites.

Lithobiomorpha
The lithobiomorpha represent the other main group of anamorphic centipedes; they also reach a mature length of 15 thoratic segments. This group has lost the compound eyes, and sometimes has no eyes altogether. Instead, it eyes have facets or groups of facets. It's spiracles are paired and can be found laterally. Every leg-bearing segment of this organism has a separate tergite. It also has relatively short antennae and legs.

Craterostigmomorpha
The craterostigmomorpha are the least diverse centipede clade, comprising only two species. . Their geographic range is restricted to the south of Africa. They have a distinct body plan; their anamorphosis comprises a single stage; they grow from 12 to 15 segments in their first moult. Their low diversity and intermediate position between the primitive Anamorphic centipedes and the derived Epimorpha has led to them being described as the "platypus of the centipede world". They represent a "highly pruned" version of a once diverse clade.

Maternal brooding unites Craterostigomomorpha with the Epimorphs into the clade Phylactometria. This trait is thought to be closely linked with the presence of sternal pores, which secrete sticky or noxious secretions, which mainly serve to repel predators and parasites. The presence of these pores on the Devonian Devonobius permits its inclusion in this clade, allowing its divergence to be dated to.

Scolopendromorpha
The more primitive of the Epimorpha, the Scolopendromorpha comprise 21 or more segments with the same number of paired legs. Their antennae have 17 or more segments. Their eyes will have at least 4 facets on each side.

Geophilomorpha
The Geophilomorpha are the most derived group of centipedes, and bear upwards of 27 leg-bearing segments. They are without fail eyeless and blind, and bear spiracles on all leg-bearing segments - in contrast to other groups, who only bear them on their 3rd, 5th, 8th, 10th and 12th segments -- a "mid-body break", accompanied by a change in tagmatic shape, occurring roughly at the interchange from odd to even segments. This group, at 1260 spp. the most diverse, also contains the largest and leggiest specimens at 29 or more pairs of legs. They also have 14 segmented antennae.

List of common species

 * Arizona tiger centipede Scolopendra polymorpha
 * Blue ring centipede Ethmostigmus trigonopodus
 * Earth centipede Pachymerium ferrugineum
 * Feather tail centipede Alipes sp.
 * Galápagos centipede Scolopendra galapagoensis
 * Giant Sonoran centipede Scolopendra heros
 * House centipede Scutigera coleoptrata
 * Peruvian giant orange leg centipede Scolopendra gigantea
 * Red-headed centipede Scolopendra morsitans
 * Stone centipede Lithobius forficatus
 * Vietnamese centipede Scolopendra subspinipes