Arthropods are invertebrate animals that form the most diverse border of the animal kingdom. These animals have the body covered by an exoskeleton known as the cuticle and form a linear series of ostensible segments, with appendages of articulated pieces. Arachnids, insects, and crustaceans are arthropods.
Experts estimate that there are more than a million species of arthropods, accounting for about 80% of all known animal species. Most arthropods are insects, and many of them are adapted for life in the air.
One of the main signs of identity of arthropods is their reproduction system, in this case we can highlight that the female is responsible for laying eggs, once fertilization has occurred by the male.
In this case, the result of this process can be of two types. Thus, from this egg an individual similar to its parents can be born directly or the birth of a larva can take place that, little by little, will transform in a process known as metamorphosis to give rise to the mentioned being.
The exoskeleton is made up of different layers. The surface layer, which is called the epicuticle, is very thin, is made up of proteins and lipids, and has a waterproofing function. The procuticle is the thickest layer of the cuticle and can be divided into exocuticle (the most rigid part) and endocuticle (flexible).
The arthropod changes its exoskeleton through a process of ecdysis (shedding or shedding its clothing)
There are several classifications that exist to determine the different types of arthropods, however the most common is to make groups of these living things based on the number of legs they have. In this way, we find four large groups:
Arthropods with six legs. Within this group would be insects.
Arthropods with eight legs. Those known as chelated are those that give it shape, such as spiders, scorpions or even horseshoe crabs. The main characteristic that defines them and differentiates them from other arthropods is that they do not have antennae.
Arthropods with ten legs. Crustaceans, that is, crabs, shrimp or lobsters.
Arthropods with more than twelve legs. In their case, the members of this group are the myriapods, that is, living things like centipedes.
Finally, we can highlight the particularity of the eyes of arthropods. These eyes can be simple, with a simple retina and a transparent cornea covering them, or compound, made up of various elements (ommatidia) that are located radially and can point in different directions.
