The chelicerates They are a subphylum of the phylum Arthropoda, whose members are characterized by presenting a first pair of appendages called chelicerae. It was first described in 1901 by the German zoologist Richard Heymons. This is a fairly broad group of organisms, its most recognized members being arachnids, such as spiders and scorpions..
Many of the chelicerates have venom glands, in which they synthesize toxins that allow them to paralyze and neutralize their prey in order to feed on them. In general, the species of this subphylum are found all over the planet.
Article index
The taxonomic classification of chelicerates is as follows:
Like all members of the Eukarya domain, chelicerates are characterized by presenting cells in which DNA is packaged within the cell nucleus, conforming to chromosomes. Likewise, they are made up of different cell types, which allows us to affirm that they are multicellular organisms..
Each of the cell types that make them up has been associated and specialized in specific functions, thus shaping the various tissues that make up the animal..
Likewise, chelicerates are organisms that have bilateral symmetry, that is, if an imaginary line is drawn through its longitudinal plane, two exactly equal halves are obtained..
The chelicerates, during their embryonic development, present the three germ layers known as ectoderm, mesoderm and endoderm. The importance of these layers lies in the fact that different types of cells and tissues develop from them that will eventually make up the adult individual..
Chelicerate animals are dioecious, which means that the sexes are separated. There are female individuals and male individuals.
Some of the species that make up this subphylum have glands that synthesize a toxic substance, a poison. This poison is used to hunt its prey or to defend itself from possible predators..
There are species in which the venom is so powerful that it can even kill an adult human being.
Like all members of the phylum Arthropoda, chelicerates have a segmented body, specifically in two tagmas, which are known as prosoma and opistosome. The prosome is what in other groups is called cephalothorax, while the opisthosoma is the abdomen.
Likewise, they have a protective covering that is mainly made up of a polysaccharide called chitin..
It is made up of an acron, which is located before the segments, and six segments.
Likewise, several of the appendices that characterize chelicerates emerge from the prosome. Among these are the chelicerae; these constitute the first pair of appendages of the animal.
The chelicerae is the characteristic element of this subphylum. Depending on the species, they have different functions, such as inoculating the poison to possible prey (arachnids). In such a way that in some species chelicerae are associated with venom-synthesizing glands..
The chelicerae are made up of pieces that are known by the name of artejos. Depending on the quantity, shape and arrangement of these, there will be three types of chelicerae:
Those joints that comprise it are, from the most distal to the most proximal: tarsus, tibia, patella, femur, trochanter and coxa. Through the latter, the pedipalp articulates with the animal's body. Likewise, depending on the species, the pedipalps will have different morphology..
Likewise, apart from the chelicerae and pedipalps, in the prosoma there are also four pairs of legs, which have the only function of the animal's locomotion..
It shapes the rest of the animal's body. It is made up of approximately 12 segments, the last of which is known as telson. Generally, no appendix is detached from this part of the body.
Its importance lies in the fact that inside there are structures belonging to the different organic systems, causing important functions related to circulation and reproduction, among others, to be carried out..
At the level of the second segment of the opistosome there is an orifice, the gonopore. This is part of the reproductive system of the animal. In male individuals it is where the sperm are released, while in the case of female sex, it is where the sperm is received for the fertilization process to occur. Likewise, in the female the gonopore is the site through which she lays the eggs..
The digestive system of chelicerates is quite straightforward. It is divided into three parts: stomodeum, mesodeo and proctodeo. In general, the digestive tract is narrow.
The stomodeus is made up of the oral cavity, which communicates with the esophagus, which is a thin and thin tube, provided with muscles. After the esophagus is the mesodeo, which contains a large number of digestive glands that secrete enzymes of this type.
The mesodeum makes its way to the proctodeum, which is the final portion of the digestive tract. The proctodean ends in an opening, the anus. This is where the substances that make up digestion waste are released.
The respiratory system is variable, depending on the habitat of the animal. Within the chelicerates, there are aquatic and terrestrial.
In the case of aquatic chelicerates, their respiratory system is made up of a system of gills. These are nothing more than a set of highly vascularized lamellae, which filter and retain the oxygen present in the water that circulates through them. Likewise, when they capture oxygen, they give up carbon dioxide.
On the other hand, in terrestrial chelicerates, such as spiders and scorpions, the respiratory system is made up of the so-called book lungs. Importantly, this system has nothing to do with the lungs of terrestrial vertebrates..
Book lungs are organs that are made up of invaginations of the integument, whose organization resembles the pages of a book. This arrangement increases the surface through which the gas exchange takes place..
As for the quantity, it varies depending on the species. There are chelicerates that have only one pair of book lungs, while there are others that have up to four pairs.
Finally, the book lungs communicate with the outside through holes known as spiracles, which open to the outside on the surface of the animal's body..
It is made up of the Malpighi tubes and a series of nephridiums. Both structures have the ability to filter waste from the blood, to release it directly into the intestine, so that it is excreted in a solid way as part of the stool..
Regarding the substances they excrete, they are nitrogen compounds mainly in the form of ammonia or ammonium.
Aquatic chelicerates can excrete through the gills, while terrestrial chelicerates, not having a wide availability of water, are forced to convert their waste to the solid state. In this way, they can be disposed of as feces..
The circulatory system of chelicerates is of the open or lagoon type. Blood circulates through an internal cavity known as a hemocele. The fluid that circulates through the chelicerate is the hemolymph.
Likewise, the main organ of the chelicerates circulatory system is a tubular heart that has a dorsal position. This has the function of pumping the hemolymph.
The chelicerate nervous system is made up of two nerve cords in a ventral position. These cords have a ganglion in each of the animal's segments.
Likewise, the brain is made up of the fusion of a pair of preoral ganglia. From this the ventral nerve cords mentioned above are detached.
Now, with regard to the sense organs, chelicerates present on the surface of their exoskeleton some extensions that look like a kind of hair whose function is to capture any tactile stimulus..
Likewise, at the level of the head they present compound eyes and ocelli that have the peculiarity of being pigmented. The latter are located in the middle of the head and the eyes in a lateral position..
Likewise, chelicerates present chemoreceptors that capture stimuli related to smell and taste..
Chelicerates are widely distributed throughout the globe. Arthropods have been a group that have had great success colonizing various environments, and within these the chelicerates have not been left behind..
Members of the Chelicerata subphylum are found in a wide variety of ecosystems, both terrestrial and aquatic. There are species that live in brackish and fresh waters, as well as in places with extreme climatic conditions, such as in places with constant snows, in large desert areas such as the Sahara or in the most recognized deserts of the American continent..
The chelicerates subphylum is classified into three classes:
-Arachnida: made up of organisms that lack antennae and have four pairs of legs, as well as a pair of chelicerae and a pair of pelipalps. Spiders, mites and scorpions belong to this group..
-Merostomata: made up of animals that do not have pedipalps, they have a fairly wide body and 5 pairs of legs. They are also purely aquatic organisms.
-Pycnogonida: made up of aquatic animals that are characterized by having the ability to blend in with the environment in which they develop, which is the seabed. They are characterized by having four pairs of legs that are sometimes very long and thick.
The chelicerates group have different food preferences. Most are carnivores, some are herbivores, parasites, detrivores, and even blood-sucking.
Due to the characteristics of the anatomy of their digestive system, chelicerates are prevented from ingesting large portions of food. Because of this, they have found it necessary to develop another way of eating.
The chelicerates have an external type digestion. This means that the processing and degradation of food occurs outside the animal's body and not inside, as would be the case. This is so mainly in carnivores.
When the chelicerates identify a prey, they capture it with their pedipalps and immediately inoculate digestive enzymes. These will act directly on the tissues of the prey, degrading them, until obtaining a kind of shapeless mush.
Now yes, the animal is able to ingest that resulting liquid substance. Once inside, the absorption of nutrients occurs at the level of the midgut or midgut. Finally, the components that are not absorbed are sent to the proctodean to be released as fecal waste..
On the other hand, in animals that are herbivores, their feeding process is simpler, since they feed on the pollen of plants, as well as their nectar..
The type of reproduction seen in chelicerates is sexual, that is, it involves the fusion of male and female sexual gametes..
In terrestrial species, internal fertilization is observed, which can be direct or indirect. While in aquatic species fertilization is external. Likewise, there are oviparous species and others that are ovoviviparous..
The process in terrestrial-type species is as follows: when it is a direct fertilization, the male directly introduces the sperm into the female's body so that they fuse with the female gametes..
In the case of indirect fertilization, the male releases a structure known as a spermatophore that contains the sperm. The female picks it up and introduces it into her body for fertilization to occur.
Once fertilization has occurred, the eggs are formed. In species that are oviparous, the female releases the eggs to the external environment, while in ovoviviparous species, the egg remains within the female's body..
Finally, after the development time has elapsed, the eggs hatch. Here there may be two cases: a larva can emerge from the eggs that will need to undergo transformation until it becomes an adult; or an individual emerges that presents the characteristics of the adults of the species, only small in size.
The chelicerates subphylum is very diverse. It covers more than 70,000 species distributed in the three classes that make it up. Among the most representative species we can mention:
It is the well-known horseshoe crab. It belongs to the class Merostomata. They have a fairly resistant exoskeleton, in addition to having five pairs of legs and spending most of their lives buried in the sand.
It is the well-known black widow spider. It is characterized by a red spot that presents at the level of the abdomen, an unequivocal sign for its identification. It synthesizes a poison that is highly toxic and that can trigger reactions in humans that range from mild to certain complications that can lead to death..
They are very poisonous scorpions that are characterized by having a dark-colored body, which can range from brown to black. They are mainly located in dry areas such as the Middle East.
Yet No Comments