PSEUDOSCORPIONS: CHARACTERISTICS, HABITAT, REPRODUCTION - BIOLOGY - 2025

The pseudoscorpions are a group of organisms belonging to the order Pseudoscorpionida. They are characterized by having an appearance very similar to that of scorpions, but without their tail. They were described in 1833 by the Swedish zoologist Carl Sundevall. It is made up of more than three thousand species that are widely distributed throughout the planet.

A curious fact about these animals is that, on occasions, they tend to use other animals to be able to move and cover great distances. They do this by attaching themselves to the body of other animals such as a flying insect, without causing any type of damage.

Specimen of Pseudoscorpion. Source: Donald Hobern from Copenhagen, Denmark

Taxonomy

The taxonomic classification of pseudoscorpions is as follows:

Domain: Eukarya

Queen: Animalia

Phylum: Arthropoda

Class: Arachnida

Order: Pseudoscorpions

characteristics

Psuedoscropions are eukaryotic organisms, since their cells have a structure called the cell nucleus, in which DNA is very well packed. They are animals made up of various types of cells that are specialized in various functions.

If an imaginary line is drawn along the longitudinal axis of a pseudoscorpion specimen, two exactly equal halves will be obtained. This is what is known as bilateral symmetry.

Likewise, pseudescorpions are characterized by being dioecious, which implies that there are female individuals and male individuals. They reproduce sexually and are oviparous.

From a morphological point of view they are very similar to scorpions, the only difference is that they lack a metasoma, which is the posterior extension that scorpions have and which houses the venom gland and the stinger.

Morphology

As with all arachnids, the body of pseudoscorpions is divided into two segments or tagmas: the cephalothorax or prosoma and the abdomen or opistosome. The members of this order are of reduced length, being between 2 mm and 8 mm.

Thanks to their resemblance to scorpions, these animals have a fearsome appearance, with colors ranging from black to reddish, going through the wide range of browns.

- Prosoma

It is the smaller segment of the two that make up the body of pseudoscorpions. It is divided into six segments called metamers. From it are born all the articulated appendages of the animal, which include a pair of chelicerae and pedipalps, as well as four pairs of legs.

The dorsal surface of the prosoma is covered by a kind of carapace known as the prosomic shield. The ventral surface is occupied almost entirely by the first artery of the appendages, that is, by the coxae.

Also in the middle of the anterior end the eyes of the animal are located. There are species that have one pair of eyes, just as there are others that have two pairs.

Cheliceros

The chelicerae of pseudoscorpions are bi-articulated and are similar to those of scorpions. They end in pincers that are useful in capturing prey and also to defend themselves from other animals.

Pedipalps

They are the longest appendages that these animals have. In addition to this, they are quite thick and robust, which gives them a fearsome look. They closely resemble the pedipalps of scorpions, which makes these animals look alike.

Pedipalps are characterized by presenting hair-shaped sensory structures called trichobotria. These are responsible for perceiving and reacting to any vibration, providing the animal with any information about the environment in which they develop.

In addition, just as the other appendages of arachnids are made up of knuckles, those of pseudoscorpions are too. The arteries that make up the pedipalps are known by the names: coxa, trochanter, femur, patella and chela.

At the distal end of the pedipalp, a mobile and a fixed finger can be seen, into which the so-called venom-synthesizing glands flow, which they use to immobilize and in some cases kill their prey.

Legs

They have a total of four pairs. They are made up of seven pieces. From distal to proximal: telotarso, basitarso, tibia, patella, femur, and trochanter. In the final joint you can see the presence of nails.

The function of the legs is related solely and exclusively to the effective movement and locomotion of the animal.

- Opistosome

It is the longest segment of the animal's body. It is divided into approximately 9 segments. Of course, the type and number of segments depends on the species in question.

- Internal anatomy

Digestive system

The digestive system of pseudoscorpions is complete. It has an entrance opening, which is the mouth and an exit opening, the anus.

The mouth is surrounded by the first pair of appendages, the chelicerae. The mouth opens into the oral cavity, which communicates directly with a short muscular tube known as the esophagus.

Immediately after the esophagus, the stomach is located, a place where various digestive enzymes are synthesized that contribute to further degrade the food eaten. After the stomach is the intestine, which is the site of absorption of nutrients.

The final part of the digestive tract is represented by the anal opening, which is where waste substances not used by the body are released.

Likewise, these individuals present an attached organ known as the hepatopancreas, which fulfills the same function as the liver and pancreas in vertebrate animals. This is nothing more than the production of various substances, mainly enzymes that intervene in the digestive process.

Respiratory system

The respiratory system that pseudoscorpions present is of the tracheal type and book lungs. This is a rudimentary and primitive respiratory system that consists of a series of tubes called tracheas that extend throughout the interior of the animal's body.

The tracheas reach the structures known as book lungs. These are nothing more than tegumentary invaginations that are stacked one on top of the other, giving the idea of ​​the pages of a book. This system has a certain advantage, since this arrangement makes it possible to expand the surface area in which the gas exchange takes place.

Each trachea communicates with the outside through holes called spiracles, which open at the level of the third and fourth segment of the opisthosoma.

Circulatory system

Pseudoscorpions have an open-type circulatory system. The main organ is represented by a heart, which has ostioli, the number of which is variable, depending on the species.

The fluid that circulates is the hemolymph, which is propelled by the heart into an aorta artery, which is responsible for transporting the fluid to all the cells of the animal's body.

Nervous system

The nervous system of pseudoscorpions is made up mainly of ganglionic groups. In this sense, they present a grouping of ganglia that function like the brain.

Next, the most important ganglionic groups are found in the esophagus and stomach. Both emit nerve fibers through which they communicate with the rudimentary brain.

Distribution and habitat

Pseudoscorpions are ubiquitous animals that have managed to colonize a wide variety of environments.

Although they can be seen in different environments, they have a predilection for those in which there is little availability of light, such as under rocks or litter. There are even species that have underground habits.

Pseudoscorpion in its habitat. Source: Pato Novoa from Valparaíso, Chile

Taking into account the temperature, there are species that have developed perfectly in environments where temperatures are kept low, even adopting hibernation mechanisms.

Likewise, pseudoscorpions are common animals in arid ecosystems where temperatures are high, such as deserts.

Reproduction

Pseudoscorpions present a type of indirect reproduction, in which fertilization is internal. This means that there is no copulation between the male and the female, but even so, fertilization occurs within the female's body.

The process is as follows: the male deposits on the ground a structure known as spermatophore, in which the sperm is contained. The female takes the spermatophore and introduces them through her genital opening.

Already inside the body, the fertilization process occurs. Later, the female lays the eggs and from these the young are born. These present the characteristics of an adult individual, although of course, smaller. In this way, it can be affirmed that pseudoscorpions are oviparous organisms with direct development.

It is important to note that there are species of pseudoscorpions that during their reproduction process contemplate curious mating rituals, such as a dance in which the male and the female hold each other through their pedipalps and move oscillatingly back and forth.

Feeding

Pseudoscorpions are predatory animals. They tend to feed on other arthropods such as mites, diptera or ants, among others. Its typical feeding mechanism involves the capture of the prey using the pedipalps and inoculating them with venom.

Taking into account the small size of pseudoscorpions, they most often have an external digestion. This means that the animal secretes digestive enzymes, which begin to degrade the prey, turning it into a kind of porridge that is ingested and absorbed by the animal.

In turn, when the prey is smaller, it is possible that it is ingested by the animal and processed inside its body.

Once inside the body, the food is subjected to the action of various digestive enzymes that are synthesized by the stomach and the hepatopancreas. Later, at the level of the intestine, the useful nutrients are absorbed to pass to the cells and thus be used and used by them.

Finally the substances that were not absorbed are expelled through the anus in the form of waste.

Representative species

The order Pseudoscorpionida includes two suborders: Epiocheirata and Locheirata. Between the two there are approximately 3,250 described species. These are grouped into about 26 families.

Dactylochelifer latreillei

They are characterized by presenting reddish claws at the distal end of their pedipalps. Its abdomen is brown, while its prosoma is darker, even black.

Dendrochernes cyrneus

It is typical of some European areas and Azerbaijan. Their pedipalps are slightly shorter than those of other pseudoscorpion species. Likewise, the penultimate artery of its pedipalps is quite thick, compared to the rest.

Titanobochica magna

Known as the giant pseudoscorpion of the Algarve caves, it has cave habits, preferring places with no light. It is characterized because its pedipalps are quite thin and the terminal artery is very elongated. It was discovered less than 10 years ago and is one of the most striking species of the order Pseudoscorpionida.

Specimen of Titanobochica magna. Source: Depths

References

1. Curtis, H., Barnes, S., Schneck, A. and Massarini, A. (2008). Biology. Editorial Médica Panamericana. 7th edition
2. Harvey, MS (2013). Pseudoscorpions of the World, version 3.0. Western Australian Museum, Perth. museum.wa.gov.au
3. Hickman, CP, Roberts, LS, Larson, A., Ober, WC, & Garrison, C. (2001). Integrated principles of zoology (Vol. 15). McGraw-Hill.
4. Ribera, I., Melic, A., Torralba, A. (2015). Introduction and visual guide of arthropods. IDEA 2 magazine. 1-30.
5. Weygoldt, P. (1969). The biology of pseudoscorpions. Cambridge, Massachusetts, Harvard University Press.
6. Zaragoza, JA 2004. Pseudoscorpions. In practical course of entomology. (Barrientos, JA Ed.): Spanish Association of Entomology; Alicante: CIBIO. Ibero-American Center for Biodiversity; Bellaterra: Autonomous University of Barcelona, ​​Servei de Publicacions: 177-187.