Cladistic analysis of the family Stenothoidae (Amphipoda, Crustacea)

The amphipod family Stenothoidae contains more than 200 species in about 40 genera; these genera are at present often defined not by the presence, but by the absence of synapomorphies, thus defining grades rather than clades. Our phylogenetic analyses yielded 4 groups of stenothoids: a basic proboloidid clade; an advanced and always clearly separated Austral-Antarctic thaumatelsonid clade, with a possibly related Arctic mesometopid clade; and finally a poorly resolved group, the stenothoids sensu stricto, including the large and probably polyphyletic genera Stenothoe and Metopa, each with more than 50 species. It is proposed to study and analyse these groups separately in future, based on better redescriptions of the individual species. Our analyses support the family status of the Thaumatelsonidae, erected as a family by Gurjanova in 1938, but reduced to subfamily rank by Barnard in 1972.