CENTIPEDES: CHARACTERISTICS, TYPES, HABITAT, FEEDING - BIOLOGY - 2024

The centipedes (Chilopoda) are a group of animals of the subphylum Myriapoda, which are characterized by a segmented body and a pair of lugs on each segment.

This class was first described in 1817 by the French entomologist Pierre André Latreille. It is a fairly large group, encompassing a total of six orders, with approximately 3300 species.

Chilopod specimen. Source: Luc.T from Buggenhout, België

The most recognized members of this class are those that belong to the Scolopendra genus, which are characterized by their robustness, their large size and the powerful poison they synthesize.

characteristics

Chilopods are multicellular organisms, because they are made up of different types of cells, each with specific functions. Likewise, the cells that comprise them are eukaryotic.

Likewise, members of this class are considered triblastic animals because during their embryonic development the three germ layers known as endoderm, mesoderm and ectoderm are found. From these layers the different cells specialize and tissues are formed.

Likewise, chilopods are heterotrophic organisms, which means that they do not have the ability to synthesize their own nutrients. On the contrary, they feed on other living beings, plants or decomposing organic matter.

When it comes to symmetry, it is clearly stated that chilopods have bilateral symmetry. This means that they are made up of two exactly equal halves. They are also oviparous, since they reproduce through egg laying.

The toxin or poison produced by chilopods and inoculated through calipers is quite potent. So much so that it is capable of killing even rodents.

Taxonomy

The taxonomic classification of centipedes is as follows:

• Domain: Eukarya
• Animalia Kingdom
• Phylum: Arthropoda
• Subphylum: Myriapoda
• Class: Chilopoda

Morphology

Gabriel fgm

-External anatomy

Chilopods are part of the group of myriapods and as such present the distinctive characteristic of the group, which is a body divided into several segments. In the case of chilopods, the segments that it presents are head and trunk.

They are also covered by a kind of cuticle made up of chitin. In certain areas this cuticle may be soft, while in other regions it is rigid and hard, forming plates called sclerites.

Head

The head is lenticular in shape and has a cephalic plate. It also has some appendices that have been modified to specialize in various functions.

First they present a pair of antennas. These are of the moniliform type, that is, they are made up of small, almost circular segments like beads of a rosary. The thickness of the antennae decreases, and as they move away from the body, they become thinner. At the base they are wide. Likewise, they exceed the head in length.

It is also made up of the so-called cephalic capsule, which serves as an anchoring place for the mandibles and maxillae. The cephalic capsule is formed by the union of several structures, among which we can mention: the labrum, which is a kind of hardened lip that is superior to the mouth, and the clipeus, which has a central location and is in an anterior position with respect to the labia.

Chilopods have several oral appendages that, as already mentioned, articulate in the cephalic capsule. First, it has a pair of jaws, which have a toothed blade at their distal end. Likewise, they present two pairs of maxillae: the first one in a ventral position with respect to the mandibles, and the second largest pair almost completely covering the first pair of maxillae.

Likewise, the first pair of appendages that would correspond to the animal's legs are also modified in structures called calipers. These are wide at their base and culminate in some species of nails. Inside are the glands that synthesize the poison that the animal uses to immobilize its prey.

Behind the antennae and in a lateral position, are the eyes of the animal, which are not very specialized and even in some species they are absent. Between the eyes and the antennae are located the so-called Tömösvary organs, which are sensitive in nature, but whose specific function has not yet been fully established by specialists.

Trunk

The trunk of the chilopods is divided into segments. The number of segments depends on the species.

The most distinctive characteristic of chilopods is that for each segment of the trunk they present a single pair of appendages that have a locomotion function.

The appendages of the terminal segment of the animal are not used for displacement. In various species they are modified and specialists suggest that chilopods use them for the reproduction process or to defend themselves from possible predators. Of course this will depend on each species.

Similarly, chilopods are considered opisthtogoneal animals. This means that the genital ducts lead to the preanal segment.

Chilopods have two genital metamers; in the first one is a pair of gonopods. These are structures that are used in the copulation process to, for example, hold the female or transfer the sperm.

In the second genital metamer the gonopore can be located. Through this hole the animal can release the sperm, in the case of male individuals, or release the eggs, in the case of female individuals.

The terminal segment, generically called the telson, has two anal-type leaflets, between which is the anus itself.

-Internal anatomy

Digestive system

The digestive system of chilopods is made up of several sections. It has an anterior, a posterior and a middle intestine. Likewise, it presents the mouth that communicates with the pharynx and esophagus. In the mouth is where the food is crushed to begin to take advantage of and process its components.

At the boundary between the foregut and the midgut there is a valve whose function is to regulate the passage of substances ingested by the animal. That valve is known as the heart valve.

Immediately after this, it makes its way to the midgut, which is slightly wider than the rest of the digestive tract. This is where the absorption of ingested nutrients mainly takes place.

The midgut communicates with the hindgut. Specifically at the site where the two communicate, the Malpighi tubes of the excretory system end. In addition, in the posterior intestine is the anus, a hole through which waste that was not absorbed and used in digestion is released.

Nervous system

Chilopods have the typical arthropod nervous system. It is made up of a neuronal accumulation in the cephalic region that is divided into three parts: proto-brain, deutobrain and tritobrain.

The proto-brain is responsible for the information that is perceived through the receptors of sight. The deutobrain processes the information captured at the antenna level. The tritobrain processes the information perceived by the different appendages of the animal, such as the oral appendages or the legs.

Likewise, the nervous system is complemented by two nerve cords in a ventral position that extend throughout the entire body of the animal. In each segment of the animal the presence of a pair of nerve ganglia can be observed that are united by transverse nerve fibers.

Circulatory system

As with all myriapods, chilopods have a lacunar, that is, open, circulatory system. A liquid called hemolymph, which is colorless, circulates through it. Cells known as prohemocytes, plasmotocytes and hemocytes are suspended in it.

Likewise, it has a heart that is tubular in shape and that in turn has some cavities, which vary in number according to the species. In each metamer, the heart has a pair of ostioles. Likewise, the cephalic aorta artery departs from the heart, towards the head region and the caudal aorta artery.

Excretory system

The excretory system of chilopods is mainly made up of structures called Malpighi tubes, which occupy practically the entire length of the animal. These flow specifically at the level of the hindgut.

Likewise, these animals present a series of glands at the cephalic level that lead to the first and second pairs of maxillae.

Regarding the substances that are excreted, the chilopods excrete nitrogen in the form of uric acid and ammonia, as well as other products that are obtained from cellular metabolism.

Respiratory system

Chilopods have a tracheal-type respiratory system, which is made up of a network of ducts called tracheas; These originate from a chamber called atrium, which opens to the outside through a blowhole.

Inside the animal, the tracheae branch out profusely until they become tubes with very small diameters that reach the cells directly.

Habitat and distribution

Chilopods are widely distributed throughout the planet. However, they have a certain predilection for those habitats in which there is ample availability of water and little amount of light.

Taking this into account, they are mainly found in forests where litter and decomposing organic matter abound. They can even live in the branches of trees in dense and humid forests, of the tropical type.

Scolopendra in its normal habitat. Source: Filo gèn '

When the environmental conditions are not suitable, the chilopods are able to dig a hole in the ground and bury themselves there several centimeters deep. There they protect themselves against inclement environmental conditions and against predators.

Feeding

Within the group of the Chilopoda class there is a wide variety of organisms, which have different food preferences.

A high percentage of chilopods are predatory carnivores. They feed on small invertebrates and, in the case of the larger centipedes, they can even feed on some reptiles and even mammals such as mice.

In this case, what happens is that the centipede, when detecting a prey through its sensory receptors, holds it with the help of its appendages and they stick the ends of the calipers in it, thus inoculating it with venom. Once this has taken effect on the prey, the chilopod proceeds to ingest it in its entirety.

On the other hand, there are chilopods that are saprophytes, that is, they feed on decomposed organic matter and there are others that can be omnivores, that eat both animals and plants.

Once the food has been ingested, it is subjected to the action of the various digestive enzymes that begin to degrade it, until it is transformed into easily assimilable substances. Absorption occurs at the level of the midgut.

Finally, metabolic waste is released through the anus.

Reproduction

The type of reproduction that is observed in chilopods is sexual, with the consequent fusion of male and female sexual gametes. Fertilization occurs inside the female's body and is indirect, since copulation does not occur.

The process is as follows: the male deposits a spermatophore on the ground, the female takes it and introduces it so that fertilization occurs inside her body.

After fertilization, the female lays the eggs, an average of between 15 and 60. Likewise, the females remain guarding them until they hatch.

Female caring for the eggs. Source: Oregon Caves National Monument

In chilopods, development is direct, so the individuals that emerge from the eggs present the characteristics of the adult individuals of the group, although, of course, they are smaller.

Breathing

The type of respiration that chilopods present is tracheal. Air enters through the spiracles and travels through the network of tracheas that make up the respiratory system.

At the level of the tracheolae, what is known as gas exchange occurs. During this process, the oxygen that is present in the air that entered, diffuses into the interior of the cells. For its part, carbon dioxide passes into the tracheae to be expelled through the spiracles.

Types (orders)

Chilopods are made up of 5 orders with active species. Likewise, they also include an order of organisms that are extinct.

The orders that are integrated under the class of chilopods are the following:

• Craterostigmomorpha
• Geophilomorpha
• Lithobiomorpha
• Scolopendromorph

Among these orders there are more than three thousand species approximately. Although they may have different characters, they have enormous similarities between them.

References

1. Brusca, RC & Brusca, GJ, (2005). Invertebrates, 2nd edition. McGraw-Hill-Interamericana, Madrid
2. Cabanillas, D. (2018). Introduction to the knowledge of chilopods (Myriapoda: Chilopoda). Arthropod World Magazine. 4. 7-18
3. Curtis, H., Barnes, S., Schneck, A. and Massarini, A. (2008). Biology. Editorial Médica Panamericana. 7th edition
4. Edgecombe, G. and Giribet, G. (2007). Evolutionary biology of Centipetes (Myriapoda: Chilopoda). Annual Review of Entomology. 52. 151-170
5. Hickman, CP, Roberts, LS, Larson, A., Ober, WC, & Garrison, C. (2001). Integrated principles of zoology (Vol. 15). McGraw-Hill.
6. Voigtländer, K. (2011) Chilopoda - Ecology. Chapter of the book The Myriapoda. Vol 1