There are about 2 million living species in the animal kingdom. All are multi-celled organisms having some features in common. Out of 2 million species, the arthropods alone are estimated to be over one million which include insects, crustaceans, and arachnids.
Animals are typically classified into two main groups; vertebrates and invertebrates. Vertebrates are animals with a backbone such as mammals, birds, and reptiles, and invertebrates are animals without a backbone like insects, spiders, worms, and jellies. Arthropods are the most diverse and numerous group of animals. They make up over 80% of all known species of animals. They live in all areas of the earth, from the deep ocean to hot, dry deserts and moist tropical rainforests.
Arthropods have several characteristics. Commonly they have an exoskeleton. Arthropods are invertebrates. They do not have a spinal cord that protects the central nervous system. And they have a hard outer covering called an exoskeleton. The exoskeleton is like the outer body of a car or a suit of armor. The function of the exoskeleton is to give the arthropod support and protect important internal organs. Arthropods have segmented bodies. All arthropods have bodies composed of segments. For example, an insect has a head, thorax and abdomen or three body segments. Spiders have only two body segments, and centipedes have twenty or more segments.
Common aquatic arthropods include crustaceans such as crabs, shrimp and lobsters. Terrestrial arthropods include insects, spiders, ticks and millipedes. Arthropods have a hard outer body covering called an exoskeleton. Made of cartoon, the exoskeleton supports and protects the animal’s body and can also help reduce water loss. To their growing, arthropods go through stages of molting, a process by which they shed their exoskeleton and grow a new one. Without an internal skeleton to support their bodies. Arthropods are usually small. Aquatic arthropods such as crabs and lobsters are often larger than land arthropods as they can use the surrounding water to support their bodies.
Arthropods have organs and body systems for digestion, breathing, circulation and reproduction. They also have a variety of different sense organs, such as simple eyes and antennae. All arthropods have bilateral symmetry and reproduced by sexual reproduction. Some arthropods have specialized internal structures that produce venom. Venom is a type of poison that is injected by a bite or sting into other animals. It can be used to kill prey or for protection against predators. Wasps, bees, spiders and scorpions are often venomous.
Arthropods have jointed appendages. Arthropods are famous for their appendages. For example, the legs of spiders and the antennae of wasps. What makes arthropods unique is that the appendages have many joints. These joints allow the arthropods to move, jump and even fly.
Arthropods have bilateral symmetry. Arthropods look the same on each side. If you run a line from the head to the toe of an arthropod, it will look the same on each side. Most mammals also have bilateral symmetry.
They have an open circulatory system. An arthropod has an open circulatory system, which uses cavities called sinuses. That moves the blood around the body. A closed system of circulation uses veins and capillaries to move blood throughout the body.
Arthropods are everywhere. They are the largest animal phylum. There are over 1 million species of arthropods, and there is a huge variety.
