Centipedes (from Neo-Latin , "hundred", and Latin , "foot") are predatory arthropods belonging to the class Chilopoda (Ancient Greek , kheilos, "lip", and Neo-Latin suffix , "foot", describing the forcipules) of the subphylum Myriapoda, an arthropod group which includes millipedes and other multi-legged animals. Centipedes are elongated segmented (metameric) animals with one pair of legs per body segment. All centipedes are venomous and can inflict painful stings, injecting their venom through pincer-like appendages known as forcipules or toxicognaths, which are actually modified legs instead of fangs. Despite the name, no species of centipede has exactly 100 legs; the number of pairs of legs is an odd number that ranges from 15 pairs to 191 pairs. and "hundred-legs".

Centipedes are predominantly generalist carnivores, hunting for a variety of prey items that can be overpowered. They have a wide geographical range, which can be found in terrestrial habitats from tropical rainforests to deserts. Within these habitats, centipedes require a moist microhabitat because they lack the waxy cuticle of insects and arachnids, causing them to rapidly lose water. Accordingly, they avoid direct sunlight by staying under cover or by being active at night.

Description

Centipedes have a rounded or flattened head, bearing a pair of antennae at the forward margin. They have a pair of elongated mandibles, and two pairs of maxillae. The first pair of maxillae form the lower lip, and bear short palps. The first pair of limbs stretch forward from the body over the mouth. These limbs, or forcipules, end in sharp claws and include venom glands that help the animal to kill or paralyze its prey.

Their size ranges from a few millimetres in the smaller lithobiomorphs and geophilomorphs to about in the largest scolopendromorphs.

Sensory organs

Many species of centipedes lack eyes. Some lack one only, but some possess a variable number of ocelli, sometimes clustered together to form true compound eyes. However, these eyes are only capable of discerning light from dark, and provide no true vision. In some species, the first pair of legs can function as sensory organs, similar to antennae; unlike the antennae of most other invertebrates, these point backwards. An unusual clustering of sensory organs found in some centipedes is the organ of Tömösváry. The organs, at the base of the antennae, consist of a disc-like structure and a central pore, with an encircling of sensitive cells. They are likely used for sensing vibrations, and may provide a weak form of hearing.

Body

Behind the head, the body consists of at least fifteen segments. Most of the segments bear a single pair of legs; the maxillipeds project forward from the first body segment, while the final two segments are small and legless. Each pair of legs is slightly longer than the pair preceding them, ensuring that they do not overlap, which reduces the chance that they will collide and trip the animal. The last pair of legs may be as much as twice the length of the first pair. The final segment bears a telson, and includes the openings of the reproductive organs. Some species are able to close their spiracles (occludable spiracles), and a few others in dry environments have evolved a waterproof cuticle. They excrete waste through a single pair of malpighian tubules. Their use varies between species, but does not include locomotion. The ultimate legs may be elongated and thin, thickened, or pincer-like. Rhysida immarginata togoensis makes a faint creaking sound when it swings its ultimate legs. Both groups of myriapods have long, multi-segmented bodies, many legs, a single pair of antennae, and the presence of postantennal organs. Centipedes have one pair of legs per segment, while millipedes have two. Their heads differ in that millipedes have short, elbowed antennae, a pair of robust mandibles and a single pair of maxillae fused into a lip; centipedes have long, threadlike antennae, a pair of small mandibles, two pairs of maxillae and a pair of large venom claws.

thumb|upright|alt=Millipede and centipede|A representative millipede and centipede (not necessarily to scale)

{|class="wikitable"

|+ Millipede versus centipede differences 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.

Development

Centipedes grow their legs at different points in their development. In the primitive condition, seen in the orders Lithobiomorpha, Scutigeromorpha, and Craterostigmomorpha, development is anamorphic: more segments and pairs of legs are grown between moults. For example, Scutigera coleoptrata, the house centipede, hatches with only four pairs of legs and in successive moults has 5, 7, 9, 11, 15, 15, 15 and 15 pairs respectively, before becoming a sexually mature adult. Life stages with fewer than 15 pairs of legs are called larval stadia (there are about five stages). After the full complement of legs is achieved, the now postlarval stadia (about five more stages) develop gonopods, sensory pores, more antennal segments, and more ocelli. All mature lithobiomorph centipedes have 15 leg-bearing segments. The Craterostigmomorpha only have one phase of anamorphosis, with embryos having 12 pairs, and adults 15. but the total number of pairs is always odd, so there are never exactly 100 legs or 100 pairs, despite the group's common name.

Centipede segments are developed in two phases. Firstly, the head gives rise to a fixed but odd number of segments, driven by Hox genes as in all arthropods. Secondly, pairs of segments are added at the tail (posterior) end by the creation of a prepattern unit, a double segment, which is then always divided into two. The repeated creation of these prepattern units is driven by an oscillator clock, implemented with the Notch signalling pathway. The segments are homologous with the legs of other arthropods such as trilobites; it would be sufficient for the Notch clock to run faster, as it does in snakes, to create more legs.

Ecology

Diet

Centipedes are predominantly generalist predators, which means they are adapted to eat a broad range of prey. Common prey items include lumbricid earthworms, dipteran fly larvae, collembolans, and other centipedes. They are carnivorous; study of gut contents suggests that plant material is an unimportant part of their diets, although they eat vegetable matter when starved during laboratory experiments.

Species of Scolopendromorpha, noticeably members from the genera Scolopendra and Ethmostigmus, are able to hunt for substantial prey items, including large invertebrates and sizable vertebrates, which could be larger than the myriapod itself. For instance, Scolopendra gigantea (the Amazonian giant centipede) preys on tarantulas, scorpions, lizards, frogs, birds, mice, snakes, and even bats, catching them in midflight. Three species (Scolopendra cataracta, S. paradoxa, and S. alcyona) are amphibious, believed to hunt aquatic or amphibious invertebrates.

Predators

thumb|A centipede ([[Scolopendra cingulata) being eaten by a European roller]]

Many larger animals prey upon centipedes, such as mongooses, mice, salamanders, beetles and some specialist snake species. They form an important item of diet for many species and the staple diet of some such as the African ant Amblyopone pluto, which feeds solely on geophilomorph centipedes, and the South African Cape black-headed snake Aparallactus capensis.

Defences

Some geophilomorph, lithobiomorph, and scolopendromorph centipedes produce sticky, toxic secretions to defend themselves. The various secretions ward off or entangle predators. Scolopendromorph secretions contain hydrogen cyanide. Among geophilomorphs, the secretions of Geophilus vittatus are sticky and odorous, and contain hydrogen cyanide.

The giant desert centipede of Arizona, Scolopendra polymorpha, has a black head and tail, and an orange body; this conspicuous pattern may<!--does not seem to have been proven--> be aposematic, an honest signal of the animal's toxicity. Many species raise and splay their ultimate legs and display the spines found on the legs in a defensive threat posture. Thus, centipedes are most commonly found in high-humidity environments to avoid dehydration, and are mostly nocturnal.

Centipedes live in many different habitats including in soil and leaf litter; they are found in environments as varied as tropical rain forests, and caves. Some geophilomorphs are adapted to littoral habitats, where they feed on barnacles.

Threatened species

According to the IUCN Red List, there are one vulnerable, six endangered, and three critically endangered species of centipede. For example, the Serpent Island centipede (Scolopendra abnormis) is vulnerable, and Turk's earth centipede (Nothogeophilus turki) and the Seychelles long-legged centipede (Seychellonema gerlachi) are both endangered.

Evolution

Fossil history

thumb|upright|[[Latzelia, a Carboniferous scutigeromorph from the Mazon Creek fossil beds. 1890 illustration by J. H. Emerton ]]

The fossil record of centipedes extends back to , during the Late Silurian (Crussolum), though they are rare throughout the Paleozoic. Another Devonian site, the Rhynie chert, also bears Crussolum fossils, Three species, one scutigeromorph (Latzelia) and two scolopendromorphs (Mazoscolopendra and the poorly known Palenarthrus), have been described from the Mazon Creek fossil beds, which are Carboniferous, 309–307 mya. More species appear in the Mesozoic, including scolopendromorphs and scutigeromorphs in the Cretaceous.

External phylogeny

The following cladogram shows the position of the Chilopoda within the arthropods as of 2019:<!-- timings: -->

Internal phylogeny

Within the myriapods, centipedes are believed to be the first of the extant classes to branch from the last common ancestor. The five orders of centipedes are: Craterostigmomorpha, Geophilomorpha, Lithobiomorpha, Scolopendromorpha, and Scutigeromorpha. These orders are united into the clade Chilopoda by the following synapomorphies:

  1. The first postcephalic appendage is modified to venom claws.
  2. The embryonic cuticle on second maxilliped has an egg tooth.
  3. The trochanter-prefemur joint is fixed.
  4. A spiral ridge occurs on the nucleus of the spermatozoon.

The Chilopoda are then split into two clades: the Notostigmophora including the Scutigeromorpha and the Pleurostigmophora including the other four orders. The following physical and developmental traits can be used to separate members of the Pleurostigmomorpha from Notostigmomorpha:

  • The spiracles are located on the sides of the centipede (in Notostigmomorphs, they are located dorsally).
  • The spiracles are deep, more complex, and always present in pairs.
  • The head is somewhat flatter.
  • The centipedes can develop through either anamorphosis or epimorphosis.

It was previously believed that Chilopoda was split into Anamorpha (Lithobiomorpha and Scutigeromorpha) and Epimorpha (Geophilomorpha and Scolopendromorpha), based on developmental modes, with the relationship of the Craterostigmomorpha being uncertain. Recent phylogenetic analyses using combined molecular and morphological characters supports the previous phylogeny. The Epimorpha still exist as a monophyletic group within the Pleurostigmophora, but the Anamorpha are paraphyletic, as shown in the cladogram:

Interaction with humans

As food

thumb|Centipedes on sticks as [[street food at Wangfujing market]]

As a food item, certain large centipedes are consumed in China, usually skewered and grilled or deep fried. They are often seen in street vendors' stalls in large cities, including Donghuamen and Wangfujing markets in Beijing.

Large centipedes are steeped in alcohol to make centipede vodka.

Hazard

Some species of centipedes can be hazardous to humans because of their bite. While a bite to an adult human is usually very painful and may cause severe swelling, chills, fever, and weakness, it is unlikely to be fatal. Bites can be dangerous to small children and those with allergies to bee stings. The venomous bite of larger centipedes can induce anaphylactic shock in such people. Smaller centipedes are generally incapable of piercing human skin.

Even small centipedes that cannot pierce human skin are considered frightening by some people due to their dozens of legs moving at the same time and their tendency to dart swiftly out of the darkness towards one's feet. A 19th-century Tibetan poet warned his fellow Buddhists, "if you enjoy frightening others, you will be reborn as a centipede."

References

Sources

  • Chilobase, a web resource for Chilopoda taxonomy. .
  • Debunking of some centipede myths – American Tarantula Society
  • Centipedes of Australia
  • Chilopoda. . Tree of Life Web Project.
  • What do you call a centipede?