Uniramia

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The Uniramia are a major group of Arthropoda, consisting of organisms with an exoskeleton, jointed appendages, and with legs that do not branch, namely the Hexapoda (insects and allies) and Myriapoda (centipedes, millipedes, and related forms). In Manton's original proposal, the Uniramia also included the Onychophora (velvet worms), but the discovery of fossil lobopods that are intermediate between onychophorans and arthropods is strong evidence for the two groups being separate.

The name Uniramia Manton, 1970 became obsolete and should be rejected because it reflected the concept of a polyphyletic group formed by the Onychophora plus the insects + myriapods. Current views in arthropod phylogeny place the Onychophora outside a monophyletic Arthropoda with some intermediate clades as the Dinocarida and the Tardigrada. Atelocerata Heymons, 1901 is the correct name of a clade uniting the Hexapoda (insects) + Myriapoda.

The phylum Uniramia are characterized by one pair of antennae and two pairs of mouthparts (single pairs of mandibles and maxillae). Their body forms and ecologies are diverse, though (in contrast to the crustaceans) most unirames are terrestrial. The Uniramia includes the insects and several smaller groups of related organisms. Note that most current classification schemes do not include the myriapods (centipedes and millipedes) in the Uniramia, instead placing them in their own subphylum, the Myriapoda (meaning "many-legged"). The evolutionary relationships between the four large subphyla mentioned are unclear.

The Crustacea were generally considered the closest relatives of the Uniramia, and sometimes these were united as Mandibulata. However, the competing hypothesis — that Crustacea and Hexapoda form a monophyletic group, the Pancrustacea, to which the Myriapoda are the closest relatives — has support from molecular and fossil evidence.