AMBLIPIGIOS: CHARACTERISTICS, TAXONOMY, HABITAT, REPRODUCTION - BIOLOGY - 2024

The amblipigios (Amblypygi) are animals that correspond to an order of the Arachnida class are characterized by pedipalpos large, and a first pair of legs extremely long and slender with sensory function. They were described for the first time in 1883 by the Swedish arachnologist Tord Tamerlan Teodor Thorell and cover a total of 140 species approximately, distributed in five families.

Although amblipygians look fearsome, with their highly developed pedipalps and in some cases spiny, they are actually totally harmless animals. They are also not poisonous, since they do not have venom glands in their chelicerae.

Damon diadema, characteristic example of the amblipigios. Source: Acrocynus

characteristics

Molting process of amblipigia. Source: Steven Acres

Amblipigia are multicellular eukaryotic organisms that have a wide variety of cells, which are specialized in various functions that contribute to the animal fulfilling its life cycle.

Likewise, due to the characteristics of their embryonic development, amblipigia are triblastic, coelomate and protostomate animals. They present the three germ layers known as endoderm, ectoderm and mesoderm, in addition to an internal cavity known as coelom. Likewise, from the blastopore (embryonic structure) both the mouth and the anus develop simultaneously.

Like the rest of the arthropods, amblipigia have radial symmetry. This is verified by drawing an imaginary line along the longitudinal axis of the animal's body, obtaining two exactly equal halves.

In another order of ideas, amblipigia are dioecious organisms, which implies that the sexes are separated, that is, there are male individuals and female individuals.

Their mating process is somewhat complex, with a ritual similar to the dance of the scorpions. Fertilization is internal, but indirect. They are oviparous organisms in which a certain parental care is observed by the female.

Likewise, like other arthropods, amblipygia undergo a molting process in which, as the animal grows, it undergoes periodic changes in its exoskeleton, releasing the old one and synthesizing a new one.

Taxonomy

The taxonomic classification of amblipigia is as follows:

• Domain: Eukarya
• Animalia Kingdom
• Phylum: arthropoda
• Subphylum: Chelicerata
• Class: Arachnida
• Order: Amblypygi

Morphology

Amblipigia are characterized by having a flattened body. Likewise, like all members of the phylum Arthropoda, it has a body divided into two segments or tagmas, which are called prosoma (anterior) and opistosoma (posterior).

-External anatomy

They are small in size, with specimens as small as 0.5 cm and others up to 4.5 cm. The characteristic color is brown or light chestnut, and there may be species that present a pattern of bands of lighter colors.

Prosoma (cephalothorax)

It is characterized by being flat and wide. It also presents on its surface the organs of vision distributed as follows: two in the upper central part and three to the sides.

The appendages are detached from this segment of the body. The first pair of appendages are the chelicerae, mouthparts found on the margin of the mouth opening. Like all appendages, they are made up of knuckles, the latter generally presenting the shape of a nail. It is important to note that these types of animals lack venom-secreting glands in chelicerae.

The second pair of appendages are the pedipalps. The morphology of these pedipalps constitutes the characteristic element of amblipigia. These are totally disproportionate compared to the dimensions of the animal's body, as well as very long. Likewise, they are covered by thorns.

Pedipalps are very useful for these animals, since they can use them both to capture their prey and to defend themselves from potential predators.

The rest of the appendages that emerge from the prosome are the four pairs of legs whose function is the movement and locomotion of the animal. They are made up of several joints: coxa, trochanter, femur, tibia, tarsus and pretarsus.

It is important to highlight that the first pair of legs of the amblipigia have sensory function, specialized in capturing tactile stimuli. These are mainly in charge of testing or exploring the terrain through which the animal moves. They are extraordinarily long, exceeding 25 cm in length. They have mechanoreceptors and chemoreceptors.

Opistosoma (abdomen)

It is narrower than the prosoma. It is divided into several segments, 12 in total. It is in this part of the body of the amblipigia that the organs that make up the different systems that comprise them are found.

At the level of the second segment is the genital orifice, which is where the reproductive organs flow. This hole is not freely exposed, but is protected by a kind of cover called an operculum.

Likewise, from the second segment, the different orifices into which the organs of the respiratory system, known as the philotracheas, flow, open.

-Internal anatomy

Digestive system

The digestive system of amblipigios is complete. This means that it has all the organs for the digestive process to occur successfully.

This begins with the mouth opening, which presents the first appendages of the animal, the chelicerae, which have a very important role in feeding, specifically in the capture of prey.

The mouth is followed by the digestive tract, which is made up first of the esophagus, followed by the stomach, the midgut, and then the final segment that empties into the anus.

They also present an attached organ known as the hepatopancreas. This fulfills functions similar to that of the pancreas and liver in other groups of living beings. Among these, the most important is the secretion of digestive enzymes that contribute to the degradation of ingested nutrients.

Nervous system

The amblipigia nervous system is quite simple, consisting essentially of neuronal groups that in turn integrate ganglia that are distributed throughout all animal segments.

At the prosome level, they present a ganglionic grouping homologous to the brain of other types of animals. This works like a central nervous system.

Organs that have nerve fibers directly connected to the rudimentary brain include the stomach and eyes. Likewise, in the upper part of the esophagus there are grouped nerve ganglia forming a kind of nerve ring that also connects with the brain.

Respiratory system

The type of respiratory system that amblipigia have is the book type of lungs. Under no circumstances do they resemble the lungs of mammals. They are much more rudimentary and primitive.

They are made up of integumentary folds that are located in pairs. These are covered by a very thin cuticle. The basic structure of each one is the following: an atrium that presents in its dorsal part a series of lamellae called philotracheas.

Each atrium communicates with the outside through holes called stigmata. It is through these holes that the air enters and leaves the animal's body.

Circulatory system

The circulatory system of amblipigia is open. The main organ of this is a tubular-type heart that is located within a cavity known as the pericardium. In this, a total of seven ostioli are opened.

An aorta artery emerges from the heart, which is responsible for distributing the hemolymph throughout the body. Likewise, the heart is suspended in place through ventral, lateral, and dorsal ligaments.

Excretory system

It is made up of structures called Malpighi tubes, which are present in all arachnids.

Malpighi's tubes open at the level of the final segment of the digestive tract, releasing the waste substances it collects there.

They also present the so-called coxal glands, which flow at the base of the first joint of the limbs, the coxa.

The main waste products of amblipigia are uric acid and guanine crystals.

Habitat and distribution

Amblipigios are animals that have an aversion to light, that is, they are lucifugal. Because of this they tend to look for dark places like under rocks and inside tree bark.

Likewise, specialists have observed with some insight that amblipigia are also located in places where there is abundant availability of water, including groundwater. This is why at a geographical level, they are located in or near tropical areas.

Very few species are found in places with high temperatures and low humidity such as deserts.

Classification

The order Amblypygi comprises a total of five families, which in turn are made up of about 140 species.

-Charinidae: corresponds to the largest amblipigium family. It is made up of three genera: Catageus, Charinus and Sarax.

-Charontidae: this family of amblipigia is characterized by having several long spines on their pedipalps, as well as other smaller ones. It is made up of two genres: Charon and

-Paracharontidae: they have pedipalps of great length, which greatly exceed the length of the animal's body. Its first pair of legs is also very long and tapers towards its distal end. It currently comprises a single genus: Paracharon.

-Phrynichidae: to this family belongs the type species of the amblipigios Damon diadema. It includes a total of seven genres: Damon, Musicodamon, Phrynichodamon, Euphrynichus, Phrynichus, Trichodamon and

-Phrynidae: they are characterized by being quite territorial. They tend to defend their space from other species of animals, even other arachnids. It is made up of four genera: Acanthophrynus, Heterophrynus, Paraphrynus and Phrynus.

Reproduction

The type of reproduction that is observed in amblipigios is sexual. This is characterized because it involves the fusion of male and female sex gametes. Likewise, fertilization is external.

The reproduction process is as follows: the male releases a structure called spermatophore in which the sperm is contained. Later a curious mating ritual begins, in which the male takes the female with the pedipalps and makes her move forward and backward until she is on the spermatophore.

Later fertilization occurs. Approximately 45 days after this is that the laying of the eggs occurs. The female can lay up to 50 eggs, which are kept in a bag that the female will carry attached to her body, in the opisthosoma, specifically in her ventral area.

Amblipigio female carrying young specimens. Source: Acrocynus

Once the embryos are ready, they hatch from the eggs. It is important to note that amblipigia have a direct development. This means that the individuals that hatch from the eggs already present the characteristics of the adult individuals of the species.

Feeding

Amblipigios are distinctly carnivorous. They feed on other smaller insects. As is well known, amblipigios flee to the light, which is why they spend the day in their dark lairs and use the darkness of night to go hunting.

As they move through the terrain, with its first pair of legs that has numerous sensory receptors, it probes the terrain, until it perceives a prey. When it does, it immediately catches it with its pedipalps to immobilize it.

Later, with the help of chelicerae, it pierces its prey and sucks their body fluids. With the help of the digestive enzymes secreted by your digestive tract, it is able to degrade nutrients to later absorb them from the intestine.

Waste substances are released through the anal opening.

Representative species

The order Amblypygi includes a total of 140 species, many of which still remain somewhat unknown to specialists. The most studied and known species of amblipigia are described below.

Damon headband

It is an emblematic species of amblipigio. It is characterized because its pedipalps are very developed, in addition to having a serrated edge. These give the animal a fearsome appearance. It has a brown color with yellowish bands. It is found in some African countries such as Ethiopia, Kenya, and Somalia, among others.

Paraphrynus mexicanus

As its name allows us to infer, this species is only found in some states of Mexico such as Oaxaca and Morelos, among other states.

Paraphrynus mexicanus. Source: Brujogomez (José Eugenio Gómez Rodríguez)

It has a dark coloration, without lighter bands. Their eyes are very well developed, which allows them to clearly visualize their prey when hunting. The length of its first pair of legs is very striking.

References

1. Curtis, H., Barnes, S., Schneck, A. and Massarini, A. (2008). Biology. Editorial Médica Panamericana. 7th edition
2. De Armas, L., Agreda, E., Trujillo, R. (2018). Synopsis of the Amblipigios (Arachnida: Amblypygi) of Guatemala. Iberian Journal of Arachnology.
3. Dunlop, JA, 1999. Reviewing the evolution of the Quelicerates. SEA, 26: 255-272.
4. Hickman, CP, Roberts, LS, Larson, A., Ober, WC, & Garrison, C. (2001). Integrated principles of zoology (Vol. 15). McGraw-Hill.
5. Marshall A., Williams, W. (1985). Zoology. Invertebrates Volume 1. Editorial Reverte
6. Ribera, I., Melic, A., Torralba, A. (2015). Introduction and visual guide of arthropods. IDEA 2 magazine. 1-30.
7. Vargas, P. & R. Zardoya (eds.) 2012. The tree of life: systematics and evolution of living beings, Madrid, 597 pp.