The Amphipoda includes a large clade defined by the presence of a previously unrecognised synapomorphy, apical robust setae on the rami of uropods 1–2. We term this clade the Senticaudata subord. nov. (Latin: sentis = thorn). It includes almost all freshwater species as well as a number of marine benthic taxa, formerly part of the ‘Gammaridea’. The phylogeny of the senticaudates was determined by cladistic analysis of morphological characters and character states. Within the suborder Senticaudata there are six infraorders: Carangoliopsida, Talitrida, Hadziida, Corophiida, Bogidiellida and Gammarida. A classification is provided and all the senticaudate families are diagnosed. We introduce for the first time in amphipod classification, the level parvorder between infraorder and superfamily. Four new families are described: Kairosidae; Eriopisidae; Nuuanuidae and Kergueleniolidae.

A morphological cladistic analysis was carried out on talitroid Amphipoda. Each character state was carefully analysed to determine whether it could be most parsimoniously ascribed to a synapomorphy or to a homoplasy. Within the Talitroidea, two new epifamilies, the Protorchestoidae and the Talitroidae, six new families, the Uhlorchestiidae, the Protorchestiidae, the Arcitalitridae, the Brevitalitridae, the Curiotalitridae and the Makawidae and three new subfamilies in the Talitridae, the Talitrinae the Floresorchestiinae and the Pseudorchestoidinae are established. A formal classification is provided to the level of subfamilies. Families and subfamilies are diagnosed.

A new species of fresh-water amphipod is described from Australia. Australomicroprotopus megacoxa gen. nov. sp. nov. It is placed in a new family, the Australomicroprotopidae fam. nov. and is fully described and figured.

A new subfamily, Platorchestiinae, is established for fifteen genera of talitrid amphipods of which three: Cocorchestia gen. nov.; Demaorchestia gen. nov. and Insularorchestia gen. nov. are new. Four new species are described: Demaorchestia hatakejima sp. nov.; D. mie sp. nov.; D. pseudojoi sp. nov. and Insularorchestia susorum sp. nov..

Amphipoda (Crustacea) from Palau, Micronesia: Families Dexaminidae, Eusiridae, Hyalidae, Ischyroceridae, Leucothoidae and Lysianassidae