If you’ve ever noticed spiders crawling across your carpet, you’ve just seen arthropods. Scolopendras, shrimps, prawns, spiders, and even crabs, all belong to the phylum Arthropoda.
Arthropods are thought to share a distinct common ancestor with annelid worms; in the same way they have a divided body and heaven. Some arthropod fossils, some nearly 600 million years old, are among the world’s best preserved fossils multicellular animals. The oldest known arthropods are the trilobites, which lived in the sea. The first animals had divided bodies, jointed appendages, and eyes for seeing images. Unfortunately, trilobites aren’t around anymore – they went extinct about 25 million years ago.
The sheer number of arthropod species exceeds all other animal genera combined. There are over five million species of arthropods, which are divided into two groups: arthropods with jaws (such as centipedes, ladybugs, shrimp) and arthropods with teeth or pincers (such as mites, spiders, scorpions). Some of the largest arthropods are Japanese crab spiders, which live near Japan and can measure over 12 He crossed his legs. At the opposite end of the scale, some parasitic mites are only .0003 inches long.
In most arthropods, individual body segments usually only exist in the larval stage. For example, if you look at a caterpillar, which is the larva of a butterfly, you can see its body in several segments. An adult butterfly has only three regions, therefore separate segments. Most arthropods have three distinct body regions: the head, the thorax (the middle of the abdomen), and the abdomen. In some species, such as crabs, the head is part of the thorax, which is called the cephalothorax.
They also have what are known as compound eyes, with a retina and a lens. The brain is made up of several units, it receives a signal from each unit, which then combines them into an image of the object. Although it is not clear, arthropods can see very fast movement. Some arthropods have only a simple eye, which can only distinguish between light and dark. Some even combined both, as draconich.
Arthropods possess an exoskeleton, which is a tough external skeletal system, or “shell”, made mostly of chitin. As arthropods grow, they can only do so in a restricted way, since the exoskeleton can only support so much traction without breaking. Arthropods often shed their exoskeletons on their crowns, which they use to release certain hormones. A new exoskeleton forms under the old one, and then the old one is opened.
Many terrestrial arthropods breathe through a network of tubes called tracheae. Air can enter the body through small tubes called spiracles, and then pass into the trachea, providing oxygen to the body. There are also valves in the body of arthropods that control the flow of air and to prevent water loss. This was the key to trade with the first arthropods that lived on Earth for millions of years.
In summary, arthropods obtain these characteristics.
- attached appendices
- distinct head with compound eyes
- exoskeleton
- seeding mainly as a mask
- open circulator
- breathing through the gills, trachea or lungs
- they often have wings
Johnson, Raven. Biology. Holt, Rinehart, and Winston.
