Arthropod joints are living organisms that are important for both the environment and humans, distinguished by their external structure surrounded by an exoskeleton.
Below on the Teketrek website, we discuss more about them, presenting their definition, characteristics, habitats, and types.
Definition of Arthropod Joints
Arthropods are animals with a true coelom and fully formed organ systems, classified as a phylum in the animal kingdom.
They comprise more than three-quarters of all animals, with approximately 900,000 recorded species, some of which are still unknown. This includes spiders, crustaceans, scorpions, insects, ticks, millipedes, and centipedes. Additionally, several fossil specimens date back to pre-Cambrian times.
Arthropods share several characteristics with annelids, including segmentation, where their bodies consist of several symmetrical segments, each with appendages that vary in function and role depending on their location in the body.
However, the question that may arise here is, what are the characteristics of arthropods?
Characteristics of arthropods
As we mentioned, the body of arthropods is primarily characterized by being composed of symmetrical segments, each carrying appendages that vary in function and role depending on their location in the body. Therefore, they are called segmented organisms.
The body of arthropods is surrounded by an exoskeleton made of chitin, which does not hinder movement.
The similarity of segments varies between each group, where some segments fuse with others to form functional regions called tagma.
Some arthropods can reach lengths of up to 70 cm, with the largest being the Japanese spider crab, which can have a width of about 4 meters including its appendages. On the other hand, the smallest individual is the parasitic woodlouse, with a body length of 0.1 mm.
The external structure of arthropods consists of a chitinous cuticle secreted by the skin, composed of two layers: the inner procuticle and the outer epicuticle.
Chitin, a hard substance linked to proteins, is composed of several nitrogenous polysaccharides that are insoluble in water, alkalis, and weak acids. It protects the animal’s body from dehydration and is shed 4 to 7 times before sexual maturity, sometimes continuing even after maturity.
Each segment of an arthropod’s body contains appendages, some of which are articulated and movable. Each appendage serves a specific function depending on its location in the body:
- Head appendages explore and manipulate food.
- Thoracic appendages assist in processing food and walking.
- Abdominal appendages aid in swimming.
These appendages consist of a primary propodite, an endopodite, and an exopodite.
The internal structure of adult arthropods features a small but hemocoel-filled body cavity, with a circulatory system starting with a contractile heart extending through a hemocoel.
Their nervous system is ringed, similar to annelids.
Arthropods have highly developed sensory organs, including compound eyes for visual perception, as well as organs for touch, taste, smell, hearing, balance, and chemical reception.
Respiration occurs through air tubes directly connected to cells or gills in aquatic species.
Arthropods habitat
Arthropods are found in various parts of the world, including polar regions, high mountainous areas, and even tropical regions.
Furthermore, some species have adapted to live in different environments, whether in the air, on land, or in water, regardless of their varying salinity levels—freshwater, saltwater, or brackish. Some species have even adapted to parasitic lifestyles, residing within the bodies of certain animals and plants.
These parasites feed on the bodies of their hosts. In the following paragraph, we’ll discuss the diet of arthropods.
Arthropods food
Arthropods are diverse animals; some are carnivorous, others are herbivorous, and there are also scavengers.
Most species of arthropods are herbivores, living in aquatic environments, either marine or freshwater, and feed on algae. Meanwhile, terrestrial species feed on plants. Now, let’s take a look at the types of arthropods in the following paragraph.
Types of arthropods
Arthropods consist of four subphyla:
1. Trilobitomorpha:
Trilobites appeared before the Cambrian period and were widespread during the Cambrian and Ordovician periods, but they became extinct about 200 million years ago.
The length of this subphylum ranges from 2 to 67 cm.
They inhabit the ocean floor, and most of them are capable of rolling up.
They have three regions: the head, thorax, and abdomen.
The head is single-piece shaped with complex eyes, mouthparts, and four pairs of appendages.
The thorax consists of multiple segments, while the abdomen is composed of fused segments.
2. Chelicerata:
Chelicerates include ancient groups such as extinct eurypterids, horseshoe crabs, scorpions, and spiders.
Chelicerates are characterized by possessing six pairs of appendages, including chelicerae, pedipalps, and four pairs of walking legs. However, horseshoe crabs have one pair of chelicerae and five pairs of walking legs.
Most chelicerates feed by sucking the blood of their prey.
3. Crustacea:
Crustaceans are aquatic organisms that inhabit both saltwater and freshwater environments, with some species found on land.
4. Uniramia:
Uniramians earn their name due to their appendages bearing a single branch, unlike other arthropods that have two branches.
Formerly known as Mandibulata, they possess a mandible for chewing.
Uniramians have a single pair of antennae for sensing and respiring through tracheal tubes.
They include five classes:
- Chilopoda or Centipedes, such as the common house centipede.
- Diplopoda or Millipedes.
- Pauropoda.
- Symphyla.
- Insects, including flies and others.
The first four groups are called Myriapods, characterized by having a body consisting of only two regions: the head and trunk.
In contrast, the body of the fifth group consists of three regions: the head, thorax, and abdomen. Appendages are located on the head and thorax, while the abdomen lacks appendages.
Frequently asked questions
How do members of the arthropod phylum breathe?
They breathe through air tubes connected directly to the cells.
In conclusion, it’s worth mentioning that arthropods are of great importance to humans. Some are consumed as food, while others provide drugs and dyes. Additionally, certain insects contribute to pollinating plants, and others produce essential materials such as silk, honey, and wax.
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