The two West-Atlantic species of Bathyporeia, B. parkeri and B. qlloddyensis are re-described. They exhibit a large number of differences with East-Atlantic and Mediterranean Bathyporeia species. Cladistic analyses of morphological characters of all known Bathyporeia species indicate that the two geographic groups are sister clades. There is strong evidence that in the genus Bathyporeia the character state 'short antennae in mature males' is the plesiomorphic condition and that'long antennae in mature males' is
the apomorphic condition. Representatives of the genera Amphiporeia, Pontoporeia and Priscillina are characterised and illustrated, as a basis of comparison with Bathyporeia. These three genera are traditionally considered to be the closest relatives of Bathyporeia and grouped together in the family Pontoporeiidae. The systematic position of these four alleged 'pontoporeiid' genera is investigated in a cladistic analysis including several other amphipods which are either morphologically similar or potentially plesiomorphic. In this analysis the monophyly of the genus Bathyporeia is supported by a very high number of synapomorphies. Bathyporeia itself forms a strongly supported clade (the Bathyporeiidae) with the genus Amphiporeia. There is no
cladistic support for a sister relationship between Bathyporeia + Amphiporeia and Pontoporeia + Priscillina. The Bathyporeiidae seem to have stronger affinities with the Gammaridae sensu stricto and especially with the Pontogammaridae. The Bathyporeiidae are therefore considered as belonging to the superfamily Gammaroidea.
Cladistic analyses of morphological characters suggest loose relationships between the genera Hallstorills, Pontoporeia and
Priscillina. However these three genera are separated by a considerable morphological gap. The morphological isolation of the genus Priscillina justifies the creation of a monotypic family Priscillinidae fam. nov. for it. The superfamily Pontoporeioidea is retained for the Pontoporeiidae and Priscillinidae fam. nov. The material of Priscillina used in this study includes a new species from Svalbard, which is described as Priscillina herrmanni sp. nov.
