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 venom claws or forcipules formed from a modified first appendage. This also means that centipedes are an exclusively predatory taxon, 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 30 cm. in the largest Scolopendromorphs. Centipedes can be found in a wide variety of environments.
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.
Some species of centipedes can be hazardous to humans because of their venomous bites. Although a bite to an adult human may only be painful, those with allergies that are similar to that of bee stings and small children are at greater risk. Smaller centipedes usually do not puncture human skin.
}} }} 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.
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.
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.
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 thoracic 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.
Centipedes are eaten by a great many vertebrates and invertebrates, 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 .
Scolopendra gigantea, also known as the Amazonian giant centipede, is the largest existing species of centipede in the world, reaching over 30 cm (12 in) in length. It is known to eat bats, catching them in midflight, as well as rodents and spiders. 'The now extinct 'Euphoberia'' was the largest 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 (25 in), although these rumours may result from the rarity of the particular centipede. Captive Galapagos centipedes don't often exceed 20 cm (8 in) in body length.
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 analysis.
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.
The lithobiomorpha represent the other main group of anamorphic centipedes; they also reach a mature length of 15 thoracic 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.
The craterostigmomorpha are the least diverse centipede clade, comprising only two species.. Their geographic range is restricted to Tasmania and New Zealand. 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 .
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.
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.