How are different groups of arthropods related?

arthropods are the largest of all animals, with more than a million species described, estimated to be 6 to 7 million. Arthropods whose name means "joined legs" are characterized by a hard exoskeleton, segmented bodies and an open circulatory system. The group includes insects, crustaceans, myriapodes (Millipedes and Centipedes), Chelicerates (Arachnids and Codes) and several extinct groups, including trilobites. Phylogenesis Arthropod is an unsatisfied scientific topic and opinions are still changing as soon as new information comes. Arthropods are almost generally considered monophyletic, which means that they come from an ordinary ancestor rather than several times. This is unlike the prevailing view in the 70s. A study of arthropods from 2001 will place a group next to Tardigrades, a phyll of microscopic aquatic animals. Both are associated with velvet worms, a group of sophisticated earth worms with a fossil record Stretching back to Cambrian or earlier (~ 545 million years). Arthropods exHe was insisting at the beginning of Cambrian, about 530 million years ago, but it is a debate about whether they had existed before. Hard cuticle, like the universal among arthropods, appear only in a fossil record about 545 million years ago.

There are currently two primary theories in terms of the location of arthropods in the tree of life. One builds arthropods next to Annelids (segmented worms) based on their shared segmentation. Newer analysis places arthropods next to the nematodes and a few small phyles, such as penis worms, based on shared feature melting. This group is called "ecdysozoa" after "ecdysis", which means melting. Molting means that the animal grows by releasing its exoskeleton, and then increases until the new exoskeleton solidifies.

Our understanding of the relationhist among arthropod groups is currently in the state of flow. One classification scheme of the 70s.Bullies, including myriapods, crustaceans and hexapods (insects), while hexapods and myriapodes were a common plus, studiocerates and the rest of the arthropods into chelerates. This classification scheme was gradually rejected when newer studies point out that hexapods are in fact nested in crustaceans (which means that the first land arthropods have evolved from crustaceans, not myriapods), with myriapods and chelerates actually sister group Myriochelata. This is called Pancrustacea hypothesis. These classifications are certain that they will be improved because more molecular and fossil data come.