Arthropods - Invertebrate PowerhousesWe'll start with the big numbers. About 75% of all animal species are arthropods. There may be more individual worms in the world, but there are more different types of arthropod than any other group on the plant. You'll find insects, spiders, crabs, lobsters, barnacles, centipedes, and even hundreds of extinct species in fossils.
Basic Structure StuffYou know the first one. Arthropods all have exoskeletons. Exoskeletons are hard outer shells made of chitin. While you have an endoskeleton, a crab has a tough shell that protects it from the outside world. Next on the list are the arms and legs. They have jointed appendages. That's what the name arthropod means. jointed leg. Inside those joints and exoskeletons are muscles that help the organisms move.
Not all exoskeletons are the same. While they may all have chitin, a shell created by the epidermis, crustaceans have an extra layer that is calcified. That calcification makes it much sturdier and much heavier. Arthropods also have very advanced sense organs. You are probably familiar with the faceted eyes of flies and antennae on insects. Those are great examples of how arthropods are prepared to interact with the world. They also have open circulatory systems. These systems circulate nutrients throughout the inside of that exoskeleton so the muscles receive all the energy needed to move quickly.
Major CategoriesThere are four major types of arthropod. Three are found around you while one group is extinct. Trilobites are an extinct group that can be found in fossils around the world. Chelicerates include species such as spiders and horseshoe crabs. Uniramians include centipedes, millipedes and the biggest group of arthropods. Insects. Crustaceans are the last category of arthropod. Crustaceans include crabs and lobsters. They are mainly aquatic species.
Cicada Swarms (BBC Video)