Poore, G.C.B., 1994. A phytogeny of the families of Thalassinidea (Crustacea: Decapoda) with keys to families and genera. Memoirs of the Museum of Victoria 54: 79-120. The confused taxonomy of the Thalassinidea (73 genera recognised here) is briefly reviewed. States of 93 characters are discussed with reference to five outgroup genera of reptant decapods. The linea thalassinica is concluded to be homologous with the linea anomurica of Anomura. Its loss in Axioidea is thought secondarily derived. Burrowing behav iour in callianassoids is coincident with loss of the interaction between the posterior margin of the carapace and anterolateral lobes on abdominal somite 1, and with loss of abdominal pleura. Characters from gills, mouthparts and pereopods are discussed. Pereopodal spiniform setae are a unifying feature of some axioids. Auxiliary surfaces on the margins of pleopods of Callianidea and Michelea are not homologous. Setal-rows, once thought to unite several genera into the CalUanideidae are shown to be more widespread and this family, as previ ously conceived, to be polyphyletic. A computer-aided phylogenetic analysis of the families, represented by 22 genera, has confirmed the monophyly of the infraorder, based largely on the unique possession of a setose lower margin to pereopod 2, The Thalassinidea are divided into three superfamilies: Thalassinoidea and Callianassoidea, more closely related to each other than to Axioidea. The Thalassinoidea contains a single family and single genus, Thalassina. Callianassoidea are divided into six families: Laomediidae, Upogebiidae, CalUanideidae, Thomassiniidae, Ctenochelidae (paraphyletic), and Callianassidae. Axioidea contain four families; Calocarididae, Axiidae, Strahlaxiidae fam. nov. and Micheleidae, The new classification differs from that of Borradaile (1903) only in the inclusion of many more taxa. The affinities between families suggested by Gurney (1938), de Saint Laurent (1973), Kensley and Heard (1991) and Sakai (1992a) are not supported. Diagnoses and keys are presented for the families and all the currently accepted genera, largely based on review of the literature and reference to museum collections. Contents