We explain to you what are the arthropods and how this group of invertebrates is classified. In addition, its main features and examples.
What are the arthropods?
It is known as artr pods a an evolutionary set (o phylum ) of invertebrate animals of complex organization, provided with an external skeleton, segmented bodies and articulated legs (from there his name: from the Greek rthron, articulaci n y po s, pie ) . It deals with animals The most numerous on the planet, adapted to any type of environment that exists, that is, are the animals with the greatest evolutionary success that exist.
One of the main characteristics of the `` arthropods '' is the segmentation of its legs and its body, joined through joints. That allow precise movements and velocities. From there, there were also various forms of articulated appendages, such as antennas, pincers, the ceros, etc.
The edge of the ` ` artery '' appeared on the earth about 570 million years ago, and due to its relationship with the morph. With the annelids (worms and worms), it is assumed that they would have evolved from them. A strong evidence of that could be possible. it will be the larval stage (in the form of caterpillars and larvae) which have many arthrodes.
Currently there are more than 1, 200, 000 species of artr pods approximately, which represents 80% of the species of animals that are known. Incidentally, of the kinds of arthropods, insects are the most numerous.
See more: Invertebrate animals.
Classification of arthropods
Arthropods are classified into four large sets or classes:
- Arachnids Endowed with chelceres, they lack wings and antennae, and have four pairs of legs. Your body is divided into cephalothorax and abdomen.
- Insects The most varied and numerous of all arthropods have a pair of antennas, three pairs of legs and two pairs of wings (functional or not). Adapted to almost any physical medium, they range from detritophages, parasites, herbivores to predators.
- Crustaceans They are mostly aquatic, with presence in the seas, or also in humid terrestrial environments. They always present a stage of nauplio larva, characteristic of their evolution as a class.
- Myriapods Provided with multiple legs and long bodies, in addition to jaws (chelicers), they are similar to insects in many things, but they are eminently terrestrial and tend to be poisonous.
Characteristics of arthropods
A typical feature of arthropods is that their body is successively segmented in a manner similar to that of annelids. In addition, they have well differentiated sections that usually respect the following order: head, thorax and abdomen, apart from their limbs or appendages.
Their bodies are also protected from their rivals or predators by a skeleton articulated and formed by chitin (a carbohydrate), which is located outside the body (exoskeleton) and covers it.
This is a problem for the animal when it comes to growing, so that the skeleton must be changed in several successive stages throughout its life . This allows the development of a new skeleton, adapted to the larger dimensions of the animal. This process is called ecdisis or molt .
On the other hand, arthropods reproduce sexually and their sexes are usually well differentiated . When fertilized, the female lays eggs from which the offspring will emerge, whose development can be direct or indirect, depending on the species:
- Direct development . When the egg hatches, an identical individual to the adult emerges, only smaller. With time and nutrition, it will grow to maturity.
- Indirect . From the egg a larva will emerge very different from the adult individual, which will grow and go through different stages of profound change, called metamorphosis, until its shape is changed to that of an adult or imago .
Some simple examples of arthropods are:
- Arachnids : spiders, scorpions, ticks, mites.
- Insects : cockroaches, praying mantises, butterflies, moths, beetles, bees, aphids, cicadas, fleas, flies, dragonflies, ants and a huge etcetera.
- Crustaceans : lobsters, crabs, shrimp, prawns, barnacles.
- Myriapods : centipede, millipede, pauropod, syphilic and moisture mealybugs.