Zootaxa 3233 (1), 52-66
Crangonyx islandicus is a groundwater amphipod species endemic to Iceland and a member of the family Crangonyctidae which is widespread throughout the Holarctic region. A previous study based on variation in nuclear genes showed that C. islandicus closest relatives are Crangonyx species from North America, where most of the species diversity of the genus occurs. In this study, we aim at describing the morphological affinities of C. islandicus with North American Crangonyx species and two Eurasian species, C. chlebnikovi and C. subterraneus. We used the morphological characters defined by Zhang & Holsinger (2003) and scored them for different populations of C. islandicus as well as for C. chlebnikovi and C. subterraneus. The molecular phylogeny of the Crangonyctidae family and the morphological character states are compared in order to detect potential convergence in the morphological traits, common in subterranean species. C. islandicus appears to be close morphologically to C. subterraneus from Europe and C. longicarpus from North America. The morphological proximity of C. islandicus and C. subterraneus is incongruent with the pattern observed from molecular data.