The animals with the greatest number of species are the arthropods, which are divided into five groups : crustaceans, myriapods, arachnids and insects. Despite their anatomical differences, all these animals share two essential characteristics: they are invertebrates and do not have an internal skeleton. This particularity is related to the etymology of the term, as arthropods means articulated feet or paws (arthron is equivalent to articulation and foot pruning). Arthropods
Main physiological aspects
Most arthropods have their bodies divided into symmetrical segments and at the same time have an external skeleton, which serves as a protective element against the threat of other predators. The bodies of some arthropods do not grow at the same speed as their outer skeleton, changing to a larger one in a process known as molting.
From the point of evolutionary life, arthropods adapt to any type of environment due to several factors: the segmentation of their organism, the exoskeleton, the articulated appendages, and powerful sensory structures. These factors allow them great mobility and a remarkable effectiveness to survive.
Some arthropods are terrestrial and others aquatic. Terrestrial ones such as the scorpion breathe through their windpipes, while aquatic ones such as lobsters breathe through their bronchi . In relation to food , it is also very diversified, since there are herbivorous arthropods (the larva is an example), carnivores (mantis religious) and omnivores (the wasps).
Regarding reproduction, arthropods have internal fertilization and are oviparous, that is, they lay eggs to reproduce. Their eggs hatch larvae, which undergo several changes (metamorphosis) until they become adults.
The question of the zoological division of arthropods depends on the number of legs
Due to the large number and variety of arthropods, zoologists classify them into four large groups depending on the number of legs they have. Thus, insects such as flies, ants and lice have six legs; scorpions and spiders are part of arachnids and have eight legs; crabs and shrimp are crustaceans and have ten legs; finally, myriapods have more than ten legs and their bodies are longer (the caterpillar and centipede are part of this group).