The order Diplura is one of three orders of non-insect hexapods within the class Entognatha. The name "diplura", or "two tails", refers to the characteristic pair of caudal appendages or filaments at the terminal end of the body.
The Protura, or proturans, and sometimes nicknamed coneheads, are very small, soil-dwelling animals, so inconspicuous they were not noticed until the 20th century. The Protura constitute an order of hexapods that were previously regarded as insects, and sometimes treated as a class in their own right.
Antennae, sometimes referred to as "feelers", are paired appendages used for sensing in arthropods.
Remipedia is a class of blind crustaceans, closely related to hexapods, found in coastal aquifers which contain saline groundwater, with populations identified in almost every ocean basin so far explored, including in Australia, the Caribbean Sea, and the Atlantic Ocean. The first described remipede was the fossil Tesnusocaris goldichi. Since 1979, at least seventeen living species have been identified in subtropical regions around the world.
The telson is the hindmost division of the body of an arthropod. Depending on the definition, the telson is either considered to be the final segment of the arthropod body, or an additional division that is not a true segment on account of not arising in the embryo from teloblast areas as other segments. It never carries any appendages, but a forked "tail" called the caudal furca may be present. The shape and composition of the telson differs between arthropod groups.
The name Apterygota is sometimes applied to a former subclass of small, agile insects, distinguished from other insects by their lack of wings in the present and in their evolutionary history; notable examples are the silverfish, the firebrat, and the jumping bristletails. Their first known occurrence in the fossil record is during the Devonian period, 417–354 million years ago. The group Apterygota is not a clade; it is paraphyletic, and not recognized in modern classification schemes. As defined, the group contains two separate clades of wingless insects: Archaeognatha comprises jumping bristletails, while Zygentoma comprises silverfish and firebrats. The Zygentoma are in the clade Dicondylia with winged insects, a clade that includes all other insects, while Archaeognatha is sister to this lineage.
Caecilius is a genus of Psocoptera from the family Caeciliusidae, the lizard barklice. Species are found all around the world.
Pancrustacea is the clade that comprises all crustaceans, including hexapods. This grouping is contrary to the Atelocerata hypothesis, in which Hexapoda and Myriapoda are sister taxa, and Crustacea are only more distantly related. As of 2010, the Pancrustacea taxon was considered well accepted, with most studies recovering Hexapoda within Crustacea. The clade has also been called Tetraconata, referring to having four cone cells in the ommatidia. This name is preferred by some scientists as a means of avoiding confusion with the use of "pan-" to indicate a clade that includes a crown group and all of its stem group representatives.
The arthropod leg is a form of jointed appendage of arthropods, usually used for walking. Many of the terms used for arthropod leg segments are of Latin origin, and may be confused with terms for bones: coxa, trochanter, femur, tibia, tarsus, ischium, metatarsus, carpus, dactylus, patella.
The Entognatha are a class of wingless and ametabolous arthropods, which, together with the insects, makes up the subphylum Hexapoda. Their mouthparts are entognathous, meaning that they are retracted within the head, unlike the insects. Entognatha are apterous, meaning that they lack wings. The class contains three orders: Collembola, Diplura and Protura. These three groups were historically united with the now-obsolete order Thysanura to form the class Apterygota, but it has since been recognized that the hexapodous condition of these animals has evolved independently from that of insects, and independently within each order. The orders might not be closely related, and Entognatha is now considered to be a paraphyletic group.
Mandibulata, is one of two major clades of living arthropods alongside Chelicerata. It comprises the extant groups Myriapoda and Pancrustacea. The name "Mandibulata" refers to the mandibles, a modified pair of limbs used in food processing, the presence of which are characteristic of most members of the group. Members of the group are referred to as mandibulates.
Rhyniella is a genus of fossil springtails (Collembola) from the Rhynie chert, which formed during the Pragian stage of the Early Devonian. One species has been described, Rhyniella praecursor. For some time it was believed to be the only hexapod from the Early Devonian
Arthropods are invertebrates in the phylum Arthropoda. They possess an exoskeleton with a cuticle made of chitin, often mineralised with calcium carbonate, a body with differentiated (metameric) segments, and paired jointed appendages. In order to keep growing, they must go through stages of moulting, a process by which they shed their exoskeleton to reveal a new one. They are an extremely diverse group, with up to 10 million species.
Springtails (Collembola) form the largest of the three lineages of modern hexapods that are no longer considered insects. Although the three orders are sometimes grouped together in a class called Entognatha because they have internal mouthparts, they do not appear to be any more closely related to one another than they are to all insects, which have external mouthparts.
Xenocarida is a proposed clade inside the subphylum Crustacea that comprises two classes that were discovered in the 20th century: Remipedia and Cephalocarida. Both groups are marine hermaphrodites. The clade was recovered as the sister groups to Hexapoda.
Wingertshellicus is an extinct genus of arthropod that has been found in Hunsrück Slate, that is located in the Rhenish Massif in Germany, and lived about 405 million years ago, during the Lower Emsian.
Tactopoda or Arthropodoidea is a proposed clade of protostome animals that includes the phyla Tardigrada and Euarthropoda, supported by various morphological observations. The cladogram below shows the relationships implied by this hypothesis.
Crustaceans are a group of arthropods that are a part of the subphylum Crustacea, a large, diverse group of mainly aquatic arthropods including decapods, seed shrimp, branchiopods, fish lice, krill, remipedes, isopods, barnacles, copepods, opossum shrimps, amphipods and mantis shrimp. The crustacean group can be treated as a subphylum under the clade Mandibulata. It is now well accepted that the hexapods emerged deep in the Crustacean group, with the completed group referred to as Pancrustacea. The three classes Cephalocarida, Branchiopoda and Remipedia are more closely related to the hexapods than they are to any of the other crustaceans.
Strudiella devonica is a species of extinct arthropod from the Devonian. It was recovered in the Strud environment from the Bois des Mouches Formation, Upper Famennian. It was originally described as the first complete Late Devonian terrestrial insect, but due to its poor state of preservation, its affinity is discussed.
