Deuteropoda is a clade of arthropods whose members are distinguished from more basal stem-group arthropods like radiodonts 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 (two branched) limbs.

The clade contains all living arthropods (i.e. chelicerates and mandibulates) as well as several fossil groups that share these characteristics (e.g. Fuxianhuiida, Megacheira, Isoxyida, and Artiopoda, the last of which includes the trilobites), 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 of Arthropoda) are often referred to as "upper stem group arthropods".

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 have a pair of pre-ocular or 'protocerebral' appendages, which presumably have evolved to be the labrum of modern living arthropods. Another distinctive characteristic ancestrally present in deuteropodans but not more basal stem-arthropods is the presence of two-branched (biramous) segmented limbs running along the body posterior to the mouth, distinct from the swimming flaps present in radiodonts and "gilled lobopodians" and the lobopods of lobopodians, though the appendages of many modern arthropods are secondarily uniramous (unbranched). Many early primitive deuteropod first appendages like those in Kylinxia and isoxyids are segmented grasping appendages that are upward (dorsally)-curling, as opposed to downward curling like the frontal appendages of radiodonts, which may represent a shared ancestral trait for most or all of Deuteropoda. It is disputed whether or not the upward-curling grasping appendage of early deuteropods are homologous (derived from the same ancestral structure) to the frontal appendage of radiodonts, to which they show strong structural similarities, or that they were convergently evolved separately.

The cladogram below is a possible panarthropod phylogeny, taking into account the differentiation between "lower stem group arthropods" (Total group Euarthropoda) and "upper stem group arthropods" (Deuteropoda), based on a phylogenetic analysis published in 2026. Not all parts of this cladogram are universally accepted, as some other studies have found a closer relationship to Chelicerata than to Mandibulata for Artiopoda, and for Megacheira to be outside crown-group Arthropoda.