Deuteropoda

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 (which is proposed to include a differentiated, titular "deutocerebral" first appendage pair, a multisegmented head, and 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".