Types of ARTHROPODS and their characteristics

Arthropods are a phylum of very diverse animals and one of the most evolutionary successful animal phyla on our planet. Not surprisingly, they are the edge within the animal kingdom that has the largest number of described species and that has the largest number of representatives on planet Earth.

There are numerous arthropod animals commonly present in human life, such as flies, butterflies or crustaceans. In this article by a TEACHER we review the types of arthropods and their characteristics. If you are interested, join us!

Index

1. Arthropod types and examples
2. Characteristics of arthropod animals
3. The internal organs of arthropods
4. Reproduction of arthropods
5. Habitats of arthropods

As we said, arthropods are the most numerous phylum of animals that exists in the world. We differentiate five subphiles, of which one is made up of extinct species. The 5 types of arthropods are as follows.

Trilobites (Trilobite)

Trilobites are a subphylum of now extinct arthropod animals that had a hard body divided into three segments. Trilobites were marine animals that disappeared during the great Triassic extinctions. Despite being extinct, its fossils are very representative of the Paleozoic era and up to 20,000 species have been described. An example of a species that was present in Spain is Serratia gordaensi.

Quelicerates (Chelicerata)

Chelicerates have a body that is divided into two parts: cephalothorax (head and thorax) and abdomen or opistoma. These arthropods do not have antennae, they have 4 pairs of legs and two pairs of mouthparts, the cheliceros (hence the name of the group) and the pedipalps, which help them with food. This group is the second in number of known species after that of insects and they inhabit all types of climates, but especially in hot climates. In this group we include arachnids, pycnogonids and merostomates. Some examples of chelicerates are:

• Mites
• Spiders
• Palpigrade
• Pseudoscorpions
• Opiliones
• Scorpions

Myriapods (Miriapoda)

Myriapods are terrestrial arthropods (although closely related to humid environments) they have a body divided into two parts: head and trunk. The trunk is divided into a large number of segments, with a multitude of pairs of legs. These arthropods have two antennae, jaws, and tracheal respiration. About 160,000 species are known divided into four groups

• Centipedes or chilopods
• Millipedes or diplopods
• Pauropods
• Symphyla

Crustaceans (Crustacea)

Crustaceans are arthropods that have five pairs of legs and a body that is divided into three parts: head, thorax and abdomen, they are provided with two pairs of antennae and a pair of maxillae. They are characterized by having birameal limbs, which means that they are branched in two parts and an articulated exoskeleton that change several times a day to allow their growth. They are fundamentally aquatic animals, present in all depths, both in salty and fresh waters. They are classified into six groups and some examples are:

• Prawns
• Crabs
• Lobsters
• Barnacles
• Sea fleas or brine shrimp

Hexapods (Hexapoda)

Hexapods is another type of arthropod; also known as insects, they are characterized by having a pair of antennae, three pairs of legs and two pairs of wings (which may be reduced or missing depending on the group). Hexapods are the most numerous group of animals on earth with up to a million known species and have adapted to all environments (although there are few in aquatic environments). There are up to ten groups of insects, including:

• Dragonflies
• Fleas
• Lice
• Flies
• Mosquitoes
• Bees
• Wasps
• Ants

The edge of the arthropods, Arthropoda from the Greek ‘articulation’ and pous ‘feet’, it is a large group of Invertebrate animals characterized by having a chitin exoskeleton, a body divided into segments and articulated appendages, which gives them their name. Currently, more than a million species of arthropods have been described that inhabit the earth, although it is estimated that there may be up to 10 million.

The arthropod species are grouped into various species, so it is difficult to collect characteristics that are common to all. For example, there is a lot of variability in terms of size of the different species, existing from microscopic species to some that reach several meters. Arthropods can live in seawater, freshwater, on land or in the air and are adapted to each of the environments in which they inhabit.

Main characteristics of arthropods

One of the characteristics of the edge that stands out the most is that have segmented bodies, each of the segments are called metamers and form a kind of repeating modules.

In addition to this segmentation, a phenomenon known as tagmatization, in which the body of an arthropod was divided into two or three distinct parts. Although these segmentations are sometimes not visible to the naked eye in all adults, it is more noticeable in embryonic forms.

Another characteristic of arthropods is the presence of a exoskeleton made up of a cuticle that covers each of the arthropod body segments and a more flexible cuticle at the junctions between segments.

This cuticle is a non-cellular material that is secreted by the animal's own epidermis. There are some species whose cuticle is covered with hairs with a tactile and locomotive function, mainly present in annelids and called ketas. The arthropod cuticle is divided into three parts:

• Epicuticle: the outermost, thinner and with a waterproofing function.
• Exocuticle: the thickest and stiffest.
• Endocuticle: the innermost one, it is quite thick but flexible.

The problem with the arthropod exoskeleton is that does not grow as the body does, so it limits the growth of the animal. To solve this problem, arthropods must shed it during growth, a process known as molting or ecdysis.

In this process the animal produces enzymes that soften and digest the lower layer of the exoskeleton and causes the rest of this skeleton to detach. Immediately, the animal is secreting a new cuticle to form the new exoskeleton. This is a process that consumes a lot of energy for the animal and until the new exoskeleton is not hardens, the animal is relatively defenseless and vulnerable, with little chance of escaping or defending itself against dangers.

Being such a large group, the diet of arthropods is highly variable, there are herbivorous, carnivorous and omnivorous species.

Like the body, the internal organs of these animals they are segmenteds. Thus, the circulatory, excretory and nervous systems of arthropods have structures that are repeated throughout the body.

• The blood of arthropods is known as hemolymph and circulates freely throughout the body, known as the open circulatory system. In arthropods, and many invertebrates, the pigment in charge of oxygen transport is called hemocyanin and contains two copper atoms, so the hemolymph appears blue.
• The respiration of arthropods can vary depending on the environment in which they live. Most typically, they breathe through a network of tangled tubes that connect the outside of the body with internal tissues and deliver oxygen directly to them. Other arthropods have primitive lungs and those that inhabit the sea breathe through gills.
• The arthropod nervous system It is quite complex to be an invertebrate and consists of a pair of nerves throughout the entire body of the animal that is divided into segments and in each one a pair of ganglia arises. There is a brain located in the head that arises from the fusion of several ganglia in a cephalization process.
• The senses of arthropods are quite developed, especially the sense of sight. The eyes of arthropods are highly variable, some species have compound eyes formed by repeated elements called ommatidia in all directions and that give them a very broad vision of the environment. In others, the eyes are simpler, simpler and give a more limited view of the environment.
• Some arthropods such as arachnids have sensors that help them pick up on chemical and tactile stimuli, known as sensilias.

The vast majority of arthropods have sexual reproduction with external fertilization in the case of aquatic arthropods and internal fertilization in aerial and terrestrial arthropods.

Arthropods are usually oviparous animalsThey lay eggs, although there are some viviparous species, such as scorpions. The development of the animal from the egg can be direct or indirect:

• At direct development, from the egg an individual is born with the appearance of an adult, but smaller.
• At indirect development, a larva emerges from the egg that gradually becomes an adult through a process of metamorphosis.

Other cases, although rarer are those of parthenogenesis where the female gives rise to a zygote without having been fertilized and it occurs mainly in crustaceans and insects. There are also cases of embryogenesis, where the larva or the young individual gives rise to a new individual through a process of fragmentation. Some parasitic or sessile species are hermaphrodites.

Arthropods are adapted to all habitats on the planet, since they are the most numerous animals on the planet. However, there are groups that preferably live in one medium or another, for example, the group of crustaceans is mainly aquatic, both in brackish and freshwater environments.

The rest of the groups, such as insects, myriapods or arachnids, live in a large number of habitats such as forests, plains, deserts, meadows or mountains.

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Hickman, C. P. (2009). Comprehensive principles of zoology (14a. ed. --.). Madrid: McGraw-Hill.