Uniramia (''uni'' – one, ''ramus'' – branch, i.e. single-branches) is a group within the

arthropod Arthropods (, (gen. ποδός)) are invertebrate animals with an exoskeleton, a segmented body, and paired jointed appendages. Arthropods form the phylum Arthropoda. They are distinguished by their jointed limbs and cuticle made of chiti ...

s. In the past this group included the Onychophora, which are now considered a separate category. The group is currently used in a narrower sense. Uniramia is one of three subphyla in the

Arthropoda Arthropods (, (gen. ποδός)) are invertebrate animals with an exoskeleton, a segmented body, and paired jointed appendages. Arthropods form the phylum Arthropoda. They are distinguished by their jointed limbs and cuticle made of chitin ...

classification suggested by

Sidnie Manton Sidnie Milana Manton (4 May 1902 – 2 January 1979) was an influential British zoologist. She is known for making advances in the field of functional morphology. She is regarded as being one of the most outstanding zoologists of the twentieth ...

. This classification divided arthropods into a three-phyla polyphyletic group, with phylum Uniramia including the

Hexapoda The subphylum Hexapoda (from Greek for 'six legs') comprises most species of arthropods and includes the insects as well as three much smaller groups of wingless arthropods: Collembola, Protura, and Diplura (all of these were once considere ...

(insects),

Myriapoda Myriapods () are the members of subphylum Myriapoda, containing arthropods such as millipedes and centipedes. The group contains about 13,000 species, all of them terrestrial. The fossil record of myriapods reaches back into the late Silurian ...

(centipedes and millipedes) and the Onychophora (velvetworms). The discovery of

fossil A fossil (from Classical Latin , ) is any preserved remains, impression, or trace of any once-living thing from a past geological age. Examples include bones, shells, exoskeletons, stone imprints of animals or microbes, objects preserved ...

lobopods The lobopodians, members of the informal group Lobopodia (from the Greek, meaning "blunt feet"), or the formally erected phylum Lobopoda Cavalier-Smith (1998), are panarthropods with stubby legs called lobopods, a term which may also be used as ...

, determined to be intermediate between onychophorans and arthropods led to the splintering of the

Lobopoda ''Lobopoda'' is a genus of comb-clawed beetles in the family Tenebrionidae. The type species is '' Lobopoda striata''. The following subgenera In biology, a subgenus (plural: subgenera) is a taxonomic rank directly below genus. In the Int ...

and Onychophora into separate groups. This redefined the Uniramia as strictly "true" arthropods with exoskeletons and jointed appendages. Uniramians have strictly uniramous appendages.

Systematics Biological systematics is the study of the diversification of living forms, both past and present, and the relationships among living things through time. Relationships are visualized as evolutionary trees (synonyms: cladograms, phylogenetic t ...

can result in rival taxonomies, and this seems to have happened to Uniramia. The name Uniramia was temporarily rejected as a polyphyletic group, but when used now refers to the subphylum consisting of the insects + myriapods. Subphylum Uniramia is characterized by uniramous (single-branching) appendages, one pair of antennae and two pairs of mouthparts (single pairs of mandibles and maxillae). Their body forms and ecologies are diverse. While most unirames are terrestrial, "some are aquatic for part or all of their life cycles." Atelocerata is described as replacing Uniramia in early twentieth-century texts (Heymons, 1901), where it was the preferred name for the category uniting the

(insects) +

; but depending on the source, the term Atelocerata may have replaced Mandibulata, be an infraphylum beneath Mandibulata, or may no longer be a valid category after closer,

cladistics Cladistics (; ) is an approach to biological classification in which organisms are categorized in groups (" clades") based on hypotheses of most recent common ancestry. The evidence for hypothesized relationships is typically shared derived cha ...

-based genetic study. The

Crustacea Crustaceans (Crustacea, ) form a large, diverse arthropod taxon which includes such animals as decapods, seed shrimp, branchiopods, fish lice, krill, remipedes, isopods, barnacles, copepods, amphipods and mantis shrimp. The crustacean group c ...

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 Pancrustacea is the clade that comprises all crustaceans and hexapods. This grouping is contrary to the Atelocerata hypothesis, in which Myriapoda and Hexapoda are sister taxa, and Crustacea are only more distantly related. As of 2010, the ...

, to which the Myriapoda are the closest relatives — has support from molecular and fossil evidence.

Notes

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References

Paleos Metazoa: Arthropoda: Uniramia

External links

Katherine McBride, Lindsey Moll, Whitney Zurat, Susquehanna University

at palaeos Arthropod taxonomy Animal subphyla