The decapods They are an order of arthropods that are characterized by presenting 10 appendages, which fulfill various functions such as helping with feeding, movement and reproduction.
This order was first described in 1802 by the French entomologist Pierre Latreille and includes a large number of well-known crustaceans such as crabs, lobsters and shrimp, among others..
These animals are found in aquatic habitats, mainly marine, at various depths and are widely distributed throughout the world geography. Although some species establish commensal relationships with other animals, most are free-living.
Decapods are animals that present a certain level of complexity. They are organisms that are considered multicellular eukaryotes, which means that all their cells present the genetic material located in a structure called the cell nucleus. Likewise, they present different types of cells, with very well established and defined functions..
This group of animals are classified within the triblastics, coelomates and protostomates. This is explained by studying its embryonic development. During this, the embryo presents the three germ layers that are known as ectoderm, endoderm and mesoderm. These layers give rise to all the tissues that make up the animal. In addition, they present bilateral symmetry, which means that they are made up of two equal halves, taking the longitudinal plane as a reference..
Likewise, they have an internal cavity known as a coelom..
These animals reproduce sexually, with internal fertilization and development, both direct and indirect. Despite this, there are also species in which there is a type of asexual reproduction, parthenogenesis.
The taxonomic classification of decapods is as follows:
Most decapods have a small body that is covered in most species by an exoskeleton that is made up of chitin. Some other species are soft-bodied.
Because decapods belong to the phylum of arthropods, they have jointed appendages. As is evident from its name, the number of appendages is 10, distributed throughout the body of the animal..
The first three pairs of appendages are found in the vicinity of the oral cavity and are used by the animal for its feeding process. The rest of the appendages found in the thorax region are known as maxillipeds. The appendages that emerge from the abdomen of the animal are called pleopods and are approximately five.
On the other hand, the appendages found in the terminal segment of the body, which corresponds to the tail, are known as uropods..
In decapods there is a certain sexual dimorphism. For example, in the case of females, pleopods are robust and very well developed, since they sometimes use them to keep their eggs safe, before they spawn. In the case of males, they only have two pairs of pleopods and their abdomen is smaller..
Within the decapods you can see a wide diversity of eating habits. There are decapods that are herbivores, others that are detritivores and the vast majority that are carnivores.
In the case of herbivorous decapods, their main food is plankton, as well as the various algae that can be found in the habitats of each species. In this sense, it is important to clarify that herbivorous species are those that live mainly in freshwater ecosystems.
On the other hand, detritivores feed on decomposing organic matter. These play a very important role within ecosystems, as they help in the circulation and incorporation of organic matter..
Finally, decapods that are carnivores feed mainly on small animals such as some echinoderms, bivalves or polychaetes. Depending on the decapod species, the way the prey is captured will be different.
The animal takes the food with its mouthparts, which are in the vicinity of the oral cavity. It is crushed with the help of the jaws and later it is entered into the mouth.
After undergoing the action of digestive enzymes, food passes from the oral cavity to the stomach through the esophagus. Importantly, the stomach is divided into two areas or zones. In the first, it is crushed and in the second, it is crushed again and then filtered.
It is in the second portion of the stomach that food is subjected to the action of a chemical that is synthesized in a very important organ called the hepatopancreas. In this liquid there is a large amount of digestive enzymes that break down the nutrients to be absorbed later..
Finally, at the level of the intestine, the absorption of nutrients occurs and what is not absorbed, is expelled out of the body, as waste or feces.
Decapods reproduce in a purely sexual way. In this type of reproduction, the fusion or union of gametes (sex cells) occurs. This is facilitated by the fact that most decapods are dioecious, that is, they have separate sexes..
Among the decapod species, it is possible to observe both polygamy and monogamy. In the first, an individual can have multiple partners to mate throughout their life, while in the second, they only have one partner in life.
The latter is particularly frequent in those species whose life habits or places in which they live restrict the possibility of encounters with other specimens. The most frequent habit in most species is polygamy.
Because decapods are an order that encompasses a large number of families and, consequently, many species, their reproduction process is quite varied and complex. One of the most outstanding aspects of this are the mating rituals, that is, the behavior patterns that some specimens have to attract the attention of the individual of the opposite sex..
In this sense, there are species in which females release pheromones into the environment. These are chemical compounds whose function is to attract individuals of the opposite sex, sending an unequivocal signal that they are ready to mate. They usually release them in the water and especially during the pre-molting phase.
Likewise, some struggles also tend to be established among males to determine which is the strongest and therefore the most apt to mate with the largest number of females and thus transmit their genes to the largest number of descendants..
Other mating rituals include traveling long distances in migratory processes for reproductive purposes, as well as the emission of certain courtship sounds..
Decapod mating occurs during times when the female experiences exoskeleton shedding. This must be so because it is the moment when accessibility to the gonopore is guaranteed.
Fertilization is internal, that is, it occurs inside the female's body. Males have a copulatory organ, into which the ducts flow directly from the testicles. Sperm are stored in a structure known as a spermatophore.
At the moment of copulation, the male introduces the spermatophore into the female's gonopore. Sometimes, fertilization does not occur immediately, but the spermatophore is stored for a time before the fusion between gametes occurs..
Decapods are oviparous animals, which means that they reproduce through eggs. Once fertilization occurs, two situations can occur: the female can immediately release the eggs to the external environment, or they can incubate them for a period of time that is variable in each species.
Now, in decapods you can see the two types of development: direct and indirect. There are species, such as some crabs, in which when the eggs hatch, individuals emerge with the characteristics of an adult, but in a juvenile state..
On the contrary, there are other species in which development is indirect. This means that larvae hatch from the eggs, which can be in different stages of evolution. They must undergo a process of metamorphosis until they acquire the characteristics of the adults of the species in question..