The Kimberley Region, a comparatively pristine region in Western Australia has yet widely escaped the impacts of urban, industrial and agricultural development due to its remoteness and rugged terrain. As a result, the Kimberley is an area of high significance for natural heritage conservation across terrestrial and marine environments. The inaccessibility of vast parts of the Kimberley has also hampered the scientific exploration of its biodiversity, rendering current knowledge of the Kimberley’s fauna and flora patchy. However, several large surveys conducted during the past four decades have improved the documentation of biotic patterns throughout the Kimberley highlighting this region as one of Australia’ s biodiversity hotspots (McKenzie, 1991; Gibson and McKenzie, 2012).
Thanks to the hallmark works of Alan Solem, the Kimberley is known to support an exceptionally diverse fauna of camaenid land snails. Solem (1979, 1981a, b, 1984, 1985, 1988, 1997) revised the entire camaenid fauna known at the time and described many new taxa, bringing the count of described species from about 30 to 120. However, this number was still based on rather patchy collections undertaken mostly at readily accessible locations along major roads and the coast. Thus, there had been little doubt that future surveys in yet un-sampled areas would unearth many additional species. Our on-going revisionary work, which has mostly been based on newly collected materials from more remote locations, has since doubled the number of known camaenid species from the Kimberley to about 260 (e.g. Köhler, 2010a, b, 2011a, b, c; Criscione et al., 2012; Köhler and Johnson, 2012; Köhler and Shea, 2012; Köhler and Criscione, 2013; Criscione and Köhler 2013a, b, c, 2014a, b).
The patterns of distribution and diversity of land snail communities throughout the Kimberley are governed by rainfall, topography, soil and vegetation types (Solem and McKenzie, 1991; Gibson and Köhler, 2012; Köhler et al., 2012), and predominantly characterised by narrow range endemism and allopatry. Previous studies of camaenids from the Kimberley mainland and from offshore islands have shown that on average species ranges are restricted to a diameter of about 20 km or even less (Solem, 1991; Cameron, 1992; Köhler, 2011b). The same works have revealed a correlation between preferred habitat and the extent of species distributions. Along the coasts, many camaenids occur in rainforest habitats (i.e., vine thickets) but not in the surrounding, more open wood- and bushland. Because rainforest vegetation is restricted to small protected pockets, such rainforest species are often narrowly endemic to one or few rainforest patches (Solem, 1991; Köhler, 2010b, 2011b, c). Further inland, however, where rainforest patches are sparse or entirely lacking, camaenid snails inhabit more open woodland and rocky habitats. Since these habitats are more widespread and less fragmented, inland species tend to have much wider ranges. However, the species richness of more xeric regions is much lower than this of the sub-humid parts of the Kimberley. The richest land snail communities are found in vine thicket patches in the high precipitation zone of the north-western coastal region between the Admiralty Gulf to the north and the Camden Sound to the south (Solem and McKenzie, 1991). Altogether fifteen camaenid genera are represented in this region, some of which have recently been revised based on comparative analyses of morphological and mitochondrial DNA differentiation, such as Baudinella Thiele, 1931 and Retroterra Solem, 1985 (Criscione and Köhler, 2014a) as well as Setobaudina Iredale, 1933 (Criscione and Köhler, 2013b).
The present study is dedicated to yet another genus occurring in the high precipitation zone, Kimberleytrachia Köhler, 2011. This genus comprises twelve presently recognised species. Almost all species occupy vine thickets between the Montague Sound and Collier Bay and within less than 50 km distance from the coast (Fig. 1).
Fig. 1. Distribution of Kimberleytrachia species in the Kimberley, Western Australia. White dots = new records, black dots = records from Solem (1979, 1985) and Köhler (2011). Scale bar = 50 km. Dashed lines indicate isohyets of average annual rainfall (in mm).
Available data indicate that Kimberleytrachia species are patchily distributed and narrowly endemic (Köhler, 2011b). As in most camaenids from the Kimberley, congeneric species are predominantly allopatric. Exceptionally three species occur in sympatry on Boongaree Island and two on Augustus Island (Köhler, 2011b).
Species now placed within Kimberleytrachia were originally affiliated with Torresitrachia Iredale, 1939 (Solem, 1979, 1985), another genus with superficially similar species having a moderately large and weakly elevated shell with wide aperture, an expanded and somewhat reflected lip and a saucer-shaped umbilicus. However, Kimberleytrachia and Torresitrachia can clearly be differentiated by features of their genitalia as well as their microscopic shell sculpture. In particular, the inner penial wall of Kimberleytrachia species does not exhibit the combination of distal pustules and proximal pilasters typical of Torresitrachia. Instead, it exhibits a combination of transverse or oblique lamellae and pilasters. Furthermore, the two genera pursue different aestivation strategies: Torresitrachia species are so-called ‘free sealers’ while Kimberleytrachia species seal themselves to hard substrates while aestivating (‘rock sealers’) (Köhler, 2011b).
Based on comparative analyses of molecular and morphological data, the present study aims to resolve the phylogenetic relationships of Kimberleytrachia with respect to other north-western Australian camaenids and to test its monophyly in particular with respect to Torresitrachia in order to revise the genus-level taxonomy. We also continue the taxonomic work of Solem (1985) and Köhler (2011b) at the species level by examining previously unstudied museum material and newly collected samples. Using a combination of anatomical and genetic features, we aim to correctly delimit species and to identify and formally describe new species.