Background: The Great Australian Bight (GAB) comprises the majority of Australia's southern coastline, but to date its deep water fauna has remained almost unknown. Recent issuing of oil and gas leases in the region has highlighted this lack of baseline biological data and established a pressing need to characterise benthic abyssal fauna. Methods: From 2013 to 2017, six large-scale systematic surveys of the GAB were conducted from 200 to 5000 m depth, constituting the deepest systematic biological sampling in Australia. Sampling was conducted on soft sediment and hard substrates, both at predetermined depth intervals along north-south transect lines and at sites of interest identified by multibeam sonar. Results: A total of 66,721 invertebrate specimens were collected, comprising 1267 species, with 401 species (32%) new to science. In addition to the novelty of the fauna, there was a high degree of rarity, with 31% of species known only from single specimens. Conclusions: In this paper, we provide an annotated checklist of the benthic invertebrate fauna of the deep GAB, supplemented with colour photos of live specimens and commentary on taxonomy, diversity and distributions. This work represents an important addition to knowledge of Australia's deep sea fauna, and will provide the foundation for further ecological, biogeographical and systematic research.

Although raphitomid snails are a dominant component of gastropod communities in deep seas worldwide, their systematics is still largely tentative. We assembled the most complete sampling of Raphitomidae from south-eastern Australia to date. Based on morphological and molecular data from this material, we produced a robust phylogenetic framework and used it to delimit genera. For the focus area, our results show a large proportion of undescribed species- and genus-level taxa, 11 of which are formally described herein. We demonstrate that the examination of purely morphological characters rarely suffices for the purpose of accurate genus delimitation. As a result, some traditionally highly diverse raphitomid genera (such as Gymnobela) turn out to be artificial assemblages of several unrelated, mostly undescribed, genus-level lineages. Our data suggest that comparable configurations of shell and radular features, observed at the genus level, commonly do not reflect true phylogenetic relationships. However, our results are inconclusive as to whether homoplasy or conservatism are the drivers of this phenomenon. Accommodating for the inevitable sampling biases, south-eastern Australia appears as a possible hotspot for both raphitomid diversity and endemism, when compared with adjacent areas.

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Vast parts of the monsoon tropics of Australia feature semi-arid habitats, which are generally thought to harbour a depauperate land snail fauna as compared to the mesic continental fringes, in particular the Australian wet tropics. However, our knowledge of land snails inhabiting these often remote environments is still very patchy. In order to improve the understanding of land snail diversity in the monsoon tropics, we revised the camaenid land snail genus Exiligada based on comprehensive collections, undertaken by use of helicopters on remote limestone outcrops in the Northern Territory and in Western Australia. Based on comparative analyses of shell and genital morphology and patterns of molecular differentiation, we recognize 15 species within Exiligada, 13 of which are newly described. In addition, we suggest a revised delimitation of the type species Exiligada negriensis, as compared to the latest available revision, by removing Exiligada qualis from its synonymy and recognizing it as a distinct species. A key for species identification is also provided. Molecular phylogenetic analyses strongly supported the monophyly of Exiligada with respect to other confamilial genera known to occur in the same geographical region. Most Exiligada species are narrowly endemic to restricted limestone outcrops that cover areas with a diameter of about 20 to 150 km. Within the distributional range of Exiligada, the ranges of up to seven species overlap but we never found more than three species to occur in sympatry at a given sampling site. We propose that species originated by allopatric differentiation, followed by secondary range expansion, leading to sympatric distributions. Our study confirms that less complex rock habitats in more xeric environments support no more than three sympatric species, this being likely to be a result of ecological exclusion.

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