Conserved shell disguises diversity in Mesodontrachia land snails from the Australian Monsoon Tropics (Gastropoda: Camaenidae)

Abstract

We comprehensively revise the taxonomy of the camaenid genus Mesodontrachia Solem, 1985, which is endemic to the Victoria River District and East Kimberley in the north‐western Australian Monsoon Tropics based on comparative analyses of key morphological features and mitochondrial DNA sequences. We examined newly collected samples from several collection sites spread over nearly 20 000 km2 of mostly inaccessible land, which represented all three currently known and three previously undescribed species. All species were initially identified as members of Mesodontrachia based on their similar, putatively typical shell. However, Mesodontrachia as so delimited was polyphyletic in a mitochondrial phylogeny with respect to several other camaenid genera from NW Australia. Contrary to the shell, we found considerable variation in the penial anatomy that was consistent with the mtDNA differentiation. To retain monophyletic taxa, we propose a revised taxonomy whereby Mesodontrachia is maintained as a monotypic taxon. In addition, four genera (Nodulabium, Ototrachia, Pseudomesodontrachia and Vincentrachia) and three species (P. gregoriana, O. compressa and N. solidum) are newly described. The shell of all these taxa is highly conserved and of little taxonomic utility. Shell similarity is attributed to a similar life style in a similar and harsh environment.

Small snails in a big place: a radiation in the semi-arid rangelands in northern Australia (Eupulmonata, Camaenidae,Nanotrachia gen. nov.)

“…In this case we found that six not closely related species were lumped together into one polyphyletic assemblage, which in fact represented five different genera with nearly identical shells. The morphological conservatism in the shell is thought to have resulted from strong selection towards a certain phenotype in species that inhabit a similar, and again comparatively harsh, environment (F. Criscione & F. Köhler, 2013b). Here, we continue our revisionary work of the Camaenidae in the VRD by studying samples of supposedly new species of a yet undescribed genus.…”

Setocallosa—a new genus and species of land snail from Arnhem Land, Australia (Stylommatophora: Camaenidae)

“…from other camaenids by a typical combination of morphological features of the shell and genital anatomy: The shell differs from most other known taxa by a combination of small size, flat shape, wide umbilicus and peculiar sculpture. While shell characters may also reflect functional constraints or adaptations to varying environments (Solem 1985;Criscione et al 2012;Criscione and Köhler 2013a), the genital anatomy confirmed the systematic distinctiveness of Setocallosa from any other Arnhem Land camaenid. The mitochondrial phylogenies revealed a basal position of Setocallosa amongst the north-western Australian Camaenidae.…”

“…2B; Table 1). Due to its dependence on environmental factors, shell size is not commonly considered a good predictor of taxonomic differentiation (Solem 1985;Criscione et al 2012;Criscione and Köhler 2013a). The scattered distribution records are presumably an artefact of poor sampling and are probably not indicative of a fragmented distribution of this species.…”

Rhagadarevisited: on the taxonomy of species from the Kimberley and Dampierland, Western Australia (Pulmonata, Camaenidae)

“…Previous studies have shown that camaenid shells may be prone to conservatism and even convergence for reflecting ecological adaptations to habitat and/or lifestyle rather than evolutionary ancestry. For example, in the Western Australian camaenids Exiligada Iredale, 1939 andMesodontrachia Solem, 1985, the presence of several cryptic taxa had been attributed to morphological stasis in shell traits due to stabilising selection from a similar but comparatively harsh environment (Criscione et al 2012;Criscione and Köhler 2013a). In Rhagada species from throughout the Kimberley, shells appear to be conserved as well and it may well be that in this group symplesiomorphic traits have been maintained as a result of their adaptive significance for species pursuing nearly identical lifestyles in very similar environments.…”