 While these do seem to form a clade, it is not fully resolved whether or not they are indeed the sister taxon of all the remaining "Synalpheus".However, a detailed cladistic study of morphological characters found well marked differences between the proposed two genera and concluded that the supposed species groups around "S. biunguiculatus"/"S. coutierei", "S. brevicarpus" and "S. neomeris" are neither clearly defined nor, as it seems, monophyletic, while the group separated in "Zuzalpheus" was clearly distinct in characters of the minor first walking legs (pereiopods), and usually distinct in some others; in all "Synalpheus sensu stricto" checked to date, the transverse setal comb on the back of the minor first pereopod dactyl is missing, and the carpus is plump (about as wide as it is long or slightly wider) and small (not longer than half the length of the palm).Moreover, their stylocerite clearly extends beyond the whole first segment of the first antennae, their scaphocerite blade is never missing, the fixed finger of the major first pereopod is about the same length as the dactyl and the uropodal exopod always has one tooth only; these traits however may be also present in some of the species separated in "Zuzalpheus" though as far as can be told, most of these differ.