por The myriapods They are a superclass of the phylum Arthropoda, which is made up of centipedes and millipedes, among other lesser-known members. The main characteristic of myriapods is that they have a clearly segmented body, from which various appendages emerge that can perform locomotion or other functions such as chewing or capturing prey.
Likewise, some of the species of myriapods synthesize toxins or poisons that they use to inoculate their prey and thus be able to swallow them without problem. However, sometimes the human being has had encounters with some poisonous species and has been the victim of its bite. In humans, the venom can cause intense allergic reactions and local inflammation.
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taxonomy
The taxonomic classification of myriapods is as follows:
– Domain: Eukarya.
– Animalia Kingdom.
– Edge: Arthropoda.
– Subphylum: Mandibulata.
– Underedge: Tracheata.
– Superclass: Myriapoda.
Characteristics
Myriapods are eukaryotic organisms, as well as multicellular. Its cells, in which the DNA is delimited within the cell nucleus, have specialized in various functions, whether digestive, excretory or reproductive, among others.
Likewise, if its embryonic development process is studied, it can be seen that during this the three germ layers appear (endoderm, mesoderm and ectoderm). Because of this they are called triblastic animals.
By drawing an imaginary line through the longitudinal plane of the animal, two exactly equal halves are obtained, which makes it possible to affirm that they present bilateral symmetry.
Likewise, myriapods are dioecious organisms. That is, the sexes are separated. There are female individuals and male individuals. In the same way, they are oviparous, since they reproduce through eggs that are laid by the female after fertilization.
Morphology
-External anatomy
The main characteristic of myriapods is that, like all arthropods, they have a body divided into segments called tagmas. Specifically, the body of myriapods is segmented into three of them: head, thorax, and abdomen. However, this division is indistinguishable to the naked eye, especially between the thorax and the abdomen.
Head
It is constituted first of all by the acron. This is nothing more than a region that is not segmented. Apart from the acron, the head is also made up of several segments, which can be 5 or 6.
The element that stands out the most from this part of the animal is the pair of antennae it presents. At the base of these, there are some pores that communicate with structures called organs of Tömösvary.
These are organs of a sensory nature that are located in pairs and, although their function has not been proven, it is believed to have to do with the detection of chemical substances (taste, smell) and hearing, among others.
Likewise, two appendages detach from the head that present a very thickened and hard basal area that can be anatomically modified with elements that can be cutting or chewing. In some species, these mandibular appendages are modified to fulfill excavating functions.
After the mandibles one or two pairs of maxillae may also be present. Of course, this depends on the species of myriapod.
A very important element in the anatomy of the head of a myriapod is the presence of modified appendages known as calipers. These are usually thick at their base and have a pincer shape.
At their end they are pointed and tend to have a blackish coloration. They are associated with venom-synthesizing glands. The calipers serve to inoculate the venom to potential prey.
Thorax – abdomen
They make up the rest of the animal’s body. It is important to note that between the thorax and the abdomen there is no anatomical element that can be taken to establish the limit between one region and another. In such a way that many specialists decide to call this area simply trunk.
The trunk is divided into segments, which are known as metameres. From each of them comes a specific number of appendages, depending on the species. For example, chilopods have only one pair of appendages, while diplopods have two pairs.
It is important to note that these appendages that detach from each segment have functions related to the locomotion of the animal. Likewise, the number of metameres is variable, according to the species. This is how there are myriapods whose body consists of about 10 segments, while there are others that can have more than 150.
-Internal anatomy
The internal anatomy of myriapods is a bit complex. They present structures that throughout their development are specialized to fulfill specific functions such as digestion, respiration and excretion, among others.
Digestive system
The system dedicated to digestion is one of the simplest that can be observed among individuals of the edge of arthropods. As in most of these, the digestive system is divided into three specialized zones: the stomodeum, the mesodeum, and the proctodeum.
It consists of a cavity called the mouth, which is continuous with the pharynx and later the esophagus. Some species have crop and gizzard. It also presents a midgut and the final segment or proctodeum.
It is important to mention that at the level of the mouth it is possible to find some salivary glands, whose function is the synthesis and secretion of saliva. Various chemical substances are dissolved in it, such as digestive enzymes that help in the processing of the food they eat.
Likewise, the cells that make up the midgut secrete a series of digestive enzymes that act on the components of the food bolus, further degrading it.
The last segment, the proctodeum, culminates in the anal orifice, into which the Malpighian tubes that are part of the excretory system also open.
Nervous system
The nervous system of myriapods could be considered highly specialized, if compared to that of other less evolved arthropods. It follows the same pattern consisting of a brain-like nerve formation, ventrally located nerve cords that extend the entire length of the animal, and nerve ganglia in each metamere.
Brain formation is the result of the union of three neuronal clusters: protocerebrum, deutocerebrum and tritocerebrum.
The protocerebrum is in charge of everything related to the secretion of endocrine-type substances and with the information collected by the organs of sight (in those species that have them).
The deutocerebrum processes all the information that is captured through the receptors present in the antennae and it is believed that, to a lesser extent, information regarding the senses of smell and taste.
The tritocerebro collects information from the different appendages that the animal has, whether they are the legs or the buccal appendages.
Regarding the sense organs, in the head you can find, apart from the Tömösvary organs, a kind of rudimentary eyes. These are characterized by not presenting ommatidia (sensory receptors that can distinguish between colors). Likewise, some species have a false compound eye.
Circulatory system
As in all arthropods, the circulatory system is open, with a kind of lagoon (hemocele) where the hemolymph arrives, which is the circulating fluid. In this liquid, the only specialized cells are amebocytes, which are responsible for coagulation among other functions.
Myriapods have a heart that is cylindrical in shape and extends the entire length of the animal. For each segment, the heart presents a pair of ostioles, as well as arteries.
An important element that occurs in this type of animal is the aorta artery, which has a cephalic direction.
Excretory system
The excretory system of myriapods is simple. It is made up of the so-called Malpighian tubes. These, of which there are one or two pairs, are blind and end at the level of the proctodeum, where they release waste substances.
Among the substances discarded by myriapods is nitrogen in the form of uric acid.
Similarly, at the level of the head, specifically in the gnatoquilar, there are some maxillary glands that are also excretory in nature.
Respiratory system
Myriapods have a tracheal-type respiratory system. They have a network of tubes called tracheas that are distributed throughout their anatomy. These tracheas communicate with the outside through holes known as spiracles.
Inside the animal, the tracheas branch into ducts whose diameter is smaller and smaller that reach each cell for gas exchange.
Habitat and distribution
The group of myriapods is widely distributed throughout the planet. They have managed to colonize a wide variety of ecosystems, except the poles.
Likewise, they are purely terrestrial animals, so it is not possible to find them in aquatic environments. Despite this, it has been established that myriapods need to live near environments with ample water availability, such as those surrounding lakes or rivers.
Similarly, specialists have recorded that myriapod species are particularly abundant and diverse in tropical areas, while in areas farther away and closer to the poles they are not so much.
Myriapods are nocturnal animals, so it is common to find them in dark places like under rocks during the day. The large predators of this superclass generally hunt at night.
Feeding
Within the group of myriapods, food preferences are widely varied. There are species that are predatory carnivores such as the Scolopendra cingulatawhich feeds on small invertebrates.
Similarly, there are species that are herbivorous, such as those belonging to the Symphyla class. As well as there are omnivorous species and that feed on small invertebrates and plants.
In this same order of ideas, the species of the Pauropoda class are saprophagous, that is, they feed on decomposing organic matter.
Now, regarding the type of digestion, both internal and external digestion are observed in myriapods.
Internal digestion is one in which the animal swallows the plant or the prey, after inoculating it with the poison, and the entire digestive process occurs inside the body of the myriapod.
In this sense, the food is subjected to the action of digestive enzymes in the mouth and pharynx to be converted into easily absorbable substances by the animal’s body.
On the other hand, in external digestion the animal secretes a series of digestive enzymes that act directly on the food to be ingested,…