Deuteropoda is a proposed

clade In biology, a clade (), also known as a Monophyly, monophyletic group or natural group, is a group of organisms that is composed of a common ancestor and all of its descendants. Clades are the fundamental unit of cladistics, a modern approach t ...

arthropods Arthropods ( ) are invertebrates in the phylum Arthropoda. They possess an arthropod exoskeleton, exoskeleton with a cuticle made of chitin, often Mineralization (biology), mineralised with calcium carbonate, a body with differentiated (Metam ...

whose members are distinguished from more basal

stem-group In phylogenetics, the crown group or crown assemblage is a collection of species composed of the living representatives of the collection, the most recent common ancestor of the collection, and all descendants of the most recent common ancestor. ...

arthropods like

radiodonts Radiodonta is an extinct order of stem-group arthropods that was successful worldwide during the Cambrian period. Radiodonts are distinguished by their distinctive frontal appendages, which are morphologically diverse and were used for a variety ...

by an anatomical reorganization of the head region, namely the appearance of a differentiated first appendage pair (the ' deutocerebral' pair), a multisegmented head, a hypostome/ labrum complex, and by bearing pairs of segmented

biramous The arthropod leg is a form of jointed appendage of arthropods, usually used for walking. Many of the terms used for arthropod leg segments (called podomeres) are of Latin origin, and may be confused with terms for bones: ''coxa'' (meaning hip, ...

(two branched) limbs. The clade contains all living

(i.e.

chelicerates The subphylum Chelicerata (from Neo-Latin, , ) constitutes one of the major subdivisions of the phylum Arthropoda. Chelicerates include the sea spiders, horseshoe crabs, and arachnids (including harvestmen, scorpions, spiders, solifuges, tic ...

and mandibulates) as well as several fossil groups that share these characteristics (e.g.

Fuxianhuiida Fuxianhuiida is an extinct clade of arthropods from the Cambrian of China. All currently known species are from Cambrian Series 2 aged deposits in Yunnan, Yunnan Province, including the Maotianshan Shales, Chengjiang biota. Although historically ...

Megacheira Megacheira ("great hands", also historically great appendage arthropods) is an extinct class of predatory arthropods defined by their possession of spined "great appendages". Their taxonomic position is controversial, with studies either consider ...

Isoxyida Isoxyids are members of the order Isoxyida and the family Isoxyidae, a group of basal arthropods that existed during the Cambrian period. It contains two genera, ''Isoxys'', with 20 species found worldwide, and ''Surusicaris'' known from a single ...

, and

Artiopoda Artiopoda is a clade of extinct arthropods that includes trilobites and their close relatives. It was erected by Hou and Bergström in 1997 to encompass a wide diversity of arthropods that would traditionally have been assigned to the Trilobitomor ...

), while excluding other fossil groups that are more 'basal' or 'primitive' (e.g. radiodonts, opabiniids and lobopodians). Members of Deuteropoda that are basal to the last common ancestor of chelicerates and mandibulates (and thus lie outside the

crown group In phylogenetics, the crown group or crown assemblage is a collection of species composed of the living representatives of the collection, the most recent common ancestor of the collection, and all descendants of the most recent common ancestor ...

of Arthropoda) are often referred to as "upper stem group arthropods".

Defining characteristics

Members of Deuteropoda are characterized by the presence of a differentiated labrum and a differentiated first ' deutocerebral' pair of appendages. In contrast, lobopodians (part of the "lower stem group") and

onychophorans Onychophora (from , , "claws"; and , , "to carry"), commonly known as velvet worms (for their velvety texture and somewhat wormlike appearance) or more ambiguously as peripatus (after the first described genus, ''Peripatus''), is a phylum of el ...

have a pair of pre-ocular or ' protocerebral' appendages, which presumably have evolved to be the labrum of modern living arthropods.

Phylogeny

The cladogram below is a possible

panarthropod Panarthropoda is a clade comprising the greatest diversity of animal groups. It contains the extant phyla Arthropoda (Euarthropoda), Tardigrada (water bears) and Onychophora (velvet worms), although the precise relationships among these remained ...

phylogeny, taking into account the differentiation between "lower stem group arthropods" and "upper stem group arthropods", based on cladograms found in Zeng et al. 2020 and O'Flynn at al. 2022. (living groups are marked in bold). Not all parts of this cladogram are widely accepted, as some studies have found Isoxyida, Megacheira, Fuxianhuiida, and/or Artiopoda to lie outside of crown group Arthropoda, while some other studies have found a closer relationship to Chelicerata than to Mandibulata for Artiopoda.

References

{{Taxonbar, from=Q112480276 Ecdysozoa unranked clades Arthropod taxonomy