Centipedes (from Neo-Latin centi-]], "hundred", and Latin language pes, pedis]], "foot") are belonging to the class Chilopoda (Ancient Greek χεῖλος]], kheilos, "lip", and Neo-Latin suffix -poda]], "foot", describing the forcipules) of the subphylum Myriapoda, an arthropod group which includes and other multi-legged animals. Centipedes are elongated segmented (metameric) animals with one pair of legs per body segment. All centipedes are and can inflict painful centipede bite, 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.[
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Centipedes are predominantly generalist carnivore, 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 . Within these habitats, centipedes require a moist microhabitat because they lack the waxy cuticle of and , causing them to rapidly lose water. Accordingly, they avoid direct sunlight by staying under cover or by being Nocturnality.
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
. 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 Lithobiomorpha and Geophilomorpha 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
. 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.
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Forcipules
Forcipules are unique to centipedes. The forcipules are modifications of the first pair of arthropod leg (the maxillipeds), forming a pincer-like appendage, just behind the head. Forcipules are not oral mouthparts, though they are used to subdue prey by injecting venom and gripping the prey animal. Venom glands run through a tube, from inside the head to the tip of each forcipule.
Body
Behind the head, the body consists of at least fifteen segments. Most of the segments bear a single pair of legs; the 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.[
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Centipedes mainly use their antennae to seek out their prey. The digestive tract forms a simple tube, with digestive glands attached to the mouthparts. Like insects, centipedes breathe through a tracheal system, typically with a single opening, or spiracle, on each body segment. They excrete waste through a single pair of malpighian tubules.[
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Ultimate legs
Just as the first pair of legs are modified into forcipules, the back legs are modified into "ultimate legs", also called anal legs, caudal legs, and terminal legs.[ They are frequently sexually dimorphic, and may play a role in mating rituals.][ Because glandular pores occur more frequently on ultimate legs than on the "walking" legs, they may serve a sensory role.][ They are sometimes used in defensive postures, and some species use them to capture prey, defend themselves against predators, or suspend themselves from objects such as branches, using the legs as pincers.][ Several species use their ultimate legs upon encountering another centipede, trying to grab the body of the other centipede.][
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Members of the genus Alipes can stridulate their leaf-like ultimate legs to distract or threaten predators.[
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Distinction from millipedes
There are many differences between millipedes and centipedes.
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Life cycle
Reproduction
Centipede reproduction does not involve copulation. Males deposit a spermatophore for the female to take up. In temperate areas, egg laying occurs in spring and summer. A few parthenogenetic species are known. Females provide parental care, both by curling their bodies around eggs and young, and by grooming them, probably to remove fungi and bacteria.[
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Centipedes are longer-lived than insects; the European Lithobius forficatus may live for 5 to 6 years, and the wide-ranging Scolopendra subspinipes can live for over 10 years.
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 ecdysis.[
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The clade Epimorpha, consisting of the orders Geophilomorpha and Scolopendromorpha, is epimorphic, meaning that all pairs of legs are developed in the embryonic stages, and offspring do not develop more legs between moults. This clade contains the longest centipedes. In the Geophilomorpha, the number of thoracic segments usually varies within species, often on a geographical basis, and in most cases, females bear more legs than males. The number of leg-bearing segments varies within each order (usually 21 or 23 in the Scolopendromorpha; from 27 to 191 in the Geophilomorpha),
Centipede segments are developed in two phases. Firstly, the head gives rise to a fixed but odd number of segments, driven by as in all arthropods.
Ecology
Diet
Centipedes are predominantly generalist predators, which means they are adapted to eat a broad range of prey. Common prey items include Lumbricidae earthworms, fly larvae, , and other centipedes.
Species of Scolopendromorph, 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.[>]
Predators
Many larger animals prey upon centipedes, such as , mice, , 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,
Defences
Some Geophilomorph, Lithobiomorph, and Scolopendromorph centipedes produce sticky, toxic secretions to defend themselves. The various secretions ward off or entangle predators.
The giant desert centipede of Arizona, Scolopendra polymorpha, has a black head and tail, and an orange body; this conspicuous pattern may be Aposematism, an honest signal of the animal's toxicity.[
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Habitat and behaviour
Because centipedes lack the waxy water-resistant cuticle of other arthropods, they are more susceptible to water loss via evaporation.
Centipedes live in many different habitats including in soil and leaf litter; they are found in environments as varied as tropical rain forests,[ deserts,]
Threatened species
According to the IUCN Red List, there are one vulnerable, six endangered, and three critically endangered species of centipede.[Pearce-Kelly, P. 1996. Scolopendra abnormis. The IUCN Red List of Threatened Species 1996: e.T20042A9138315. . Accessed on 10 January 2023.][Macadam, C. 2022. Nothogeophilus turki. The IUCN Red List of Threatened Species 2022: e.T123669218A123674269. . Accessed on 10 January 2023.][Gerlach, J. 2014. Seychellonema gerlachi. The IUCN Red List of Threatened Species 2014: e.T201495A15280805. . Accessed on 10 January 2023.]
Evolution
Fossil history
The fossil record of centipedes extends back to , during the Late Silurian ( Crussolum),[ The Devonian Panther Mountain Formation contains two species of centipede. One is a species of the scutigeromorph Crussolum. The other is Devonobius, which is included in the extinct group Devonobiomorpha.][ and possible scutigeromorph head material. Rhyniognatha, which was once thought to be the oldest insect fossil, is also found in the Rhynie Chert.]
External phylogeny
The following cladogram shows the position of the Chilopoda within the arthropods as of 2019:
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 synapomorphy:
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The first postcephalic appendage is modified to venom claws.
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The embryonic cuticle on second maxilliped has an egg tooth.
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The trochanter–prefemur joint is fixed.
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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:
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The spiracles are located on the sides of the centipede (in Notostigmomorphs, they are located dorsally).
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The spiracles are deep, more complex, and always present in pairs.
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The head is somewhat flatter.
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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 paraphyly, as shown in the cladogram:[
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Evolution of venoms
All centipedes are venomous. Over the first 50 million years of the clade's evolutionary history, centipede venoms appear to have consisted of a simple cocktail of about four different components, and differentiation into specific venom types appears to have only occurred after the currently recognized five orders had developed. The evolution of the venom includes horizontal gene transfer, involving bacteria, fungi and .
Interaction with humans
As food
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 Anaphylaxis 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.[Zabs-Dkar Tshogs-Drug-Ran-Grol. The Life of Shabkar: The Autobiography of a Tibetan Yogin. Albany: SUNY Press, 1994. p. 295.]
Sources
External links
