Phylogeny and biogeography of the Gnathiidae (Crustacea: Isopoda) with descriptions of new genera and species, most from southeastern Australia

Phylogeny and biogeography of the Gnathiidae (Crustacea: Isopoda) with descriptions of new genera and species, most from south-eastern Australia.Memoirs ol the Museum of Victoria 54 (2): 271-397 The classification of the Gnathiidae is reviewed for the first time since Monod (1926).States of 72 characters are discussed with reference to two outgroups of Flabellifera, forming the basis of a phylogenetic analysis.Ninety-five species are included in the analysis rep- resenting all nominal genera and subgenera and covering the perceived variation in the family.Results indicate that the Gnathiidae can be divided into two principal clades rep- resenting one (Thawnastognathia Monod) and nine genera (Gibbagnathia gen.nov., Para- gnathia Omer-Cooper and Omer-Cooper, Euneognathia Stebbing, Bythognathia Camp, Monodgnathia gen.nov., Bathygnathia Dollfus.Caecognathia Dollfus, Gnathia Leach and Elaphognathia Monod).The new classification differs from that of Monod (1926) in the description of two new genera (Monodgnathia and Gibbagnathia), the revival of another genus previously in syn- onymy (Caecognathia), the elevation of a subgenus to generic rank (Elaphognathia) and the loss of two genera and a subgenus in synonymy (Heterognathia, Akidognathia and Peri- gnathia).The elevation of Elaphognathia to generic rank relies on the recognition of paraphyletic Gnathia.A key to the proposed genera of Gnathiidae is presented.Twenty-five new species are described and figured from south-eastern Australia, three from deep water in theTasmanand Coral Seas, and one from New Zealand.Thawnasto- gnathia is recorded for the first time since 1926.Bathygnathia, Monodgnathia, and Thau- mastognathia are recorded for the first time from Australian waters.Keys to all 45 Australian species are offered with figures of the cephalosomes of the 17 previously described species to aid identification.Habitat and distributional data for all Australian species are presented.The phylogenetic analysis of the family suggests the most significant evolutionary events in the radiation of the family took place in the cold waters of the southern hemisphere.Thawnastognathia, sister group of all other gnathiids, is an endemic genus of four species from the Australian-New Zealand shelf.Gibbagnathia, the second clade, is an endemic, monotypic genus confined to Bass Strait, southern Australia.Paragnalhia is enigmatic in being a single Afro-European species but Euneognathia is a single species from the Antarctic shelf.None of these four genera has radiated successfully.Bythognathia ( 1 species) is from the deep sea (4000 m) of the Caribbean.Monodgnathia (4 species) and Bathognathia (12 species) are both confined to the slope and deep sea.But radiation has been moderate and with the exception of the one species of Bythognathia none is found very deep, unlike many other families of isopods.Two related clades have radiated strongly in more shallow and warmer waters: Caeco- gnathia with 43 species distributed more towards the poles than Gnathia-Elaphognathia (89 species.)which is more cosmopolitan on temperate and tropical shelves and upper slopes.Small clades of species of Caecognathia are confined to Australia.Other species of the highly endemic southern Australian fauna seem to have arisen locally and independently.