Conserved shell disguises diversity inMesodontrachialand snails from the Australian Monsoon Tropics (Gastropoda: Camaenidae)

Adapting mark-recapture methods to estimating accepted species-level diversity: a case study with terrestrial Gastropoda

We introduce a new method of estimating accepted species diversity by adapting mark-recapture methods to comparisons of taxonomic databases. A taxonomic database should become more complete over time, so the error bar on an estimate of its completeness and the known diversity of the taxon it treats will decrease. Independent databases can be correlated, so we use the time course of estimates comparing them to understand the effect of correlation. If a later estimate is significantly larger than an earlier one, the databases are positively correlated, if it is significantly smaller, they are negatively correlated, and if the estimate remains roughly constant, then the correlations have averaged out. We tested this method by estimating how complete MolluscaBase is for accepted names of terrestrial gastropods. Using random samples of names from an independent database, we determined whether each name led to a name accepted in MolluscaBase. A sample tested in August 2020 found that 16.7% of tested names were missing; one in July 2021 found 5.3% missing. MolluscaBase grew by almost 3,000 accepted species during this period, reaching 27,050 species. The estimates ranged from 28,409 ± 365 in 2021 to 29,063 ± 771 in 2020. All estimates had overlapping 95% confidence intervals, indicating that correlations between the databases did not cause significant problems. Uncertainty beyond sampling error added 475 ± 430 species, so our estimate for accepted terrestrial gastropods species at the end of 2021 is 28,895 ± 630 species. This estimate is more than 4,000 species higher than previous ones. The estimate does not account for ongoing flux of species into and out of synonymy, new discoveries, or changing taxonomic methods and concepts. The species naming curve for terrestrial gastropods is still far from reaching an asymptote, and combined with the additional uncertainties, this means that predicting how many more species might ultimately be recognized is presently not feasible. Our methods can be applied to estimate the total number of names of Recent mollusks (as opposed to names currently accepted), the known diversity of fossil mollusks, and known diversity in other phyla.

Repeated evolution of an undescribed morphotype of Rhagada (Gastropoda : Camaenidae) from the inland Pilbara, Western Australia

An undescribed small, banded morphotype of Rhagada land snails occurs widely in the rocky inland Pilbara region, Western Australia. Phylogenetic analysis of mitochondrial COI and 16S rRNA genes revealed that this novel morphotype is polyphyletic, comprising four distinct major clades, with divergences up to 21.4% at COI. These clades are apparently morphologically cryptic, with no obvious shell differences. Two of these species are associated with the major clade of Rhagada in the Pilbara mainland, one of which appears to be a variant of the larger, more globose species R. pilbarana, which occurs within 20km proximity. The other two small, banded species are phylogenetically distinct from each other and all other known Rhagada. This small, banded morphotype shows evidence for both plesiomorphy and homoplasy. The morphotype has evolved independently at least twice, and is associated with the reasonably uniform habitat and harsh conditions in the elevated hinterland of the inland Pilbara. The broad distribution of the inland, small, banded morphotype conforms to the pattern of broad-scale uniformity of shells of the more coastal species of Rhagada. Its repeated evolution, however, confirms that the morphological uniformity is not simply because of common ancestry, supporting the theory that shell form in Rhagada is adapted to a broadly homogenous environment. Shell morphology in this genus has been demonstrated on more than one occasion to have the potential to adapt to different available environments, and hence shells should be used with a degree of caution for taxonomic interpretation.

Molecular phylogeny of the limacoid snail family Dyakiidae in Southeast Asia, with the description of a new genus and species

Members of the terrestrial snail family Dyakiidae from Southeast Asia show a distinct geographical distribution pattern and possess different degrees of complexity in their amatorial organ gland. This study is the first molecular phylogeny of ten of the 12 genera in this family, performed to provide insights into the origin of Dyakiidae and the evolution of their shells and amatorial organ gland structure. A new genus and new species, Pseudoquantula lenticularis Jirapatrasilp & Panha gen. & sp. nov., was uncovered based on its distinct morphological characters and molecular divergence. All other genera were retrieved as monophyletic except for Dyakia. Mainland Southeast Asia was inferred to be the ancestral range of the Dyakiidae, and the lineages then dispersed to and diversified in Borneo. Cladistic analysis showed that all 14 morphological characters used in this study were homoplastic. These results disagree with the previous amatorial organ transformation series, in which neither Pseudoplecta nor Quantula was ancestral to the other genera. The enigmatic genus Pseudoplecta, which lacks an amatorial organ gland, exhibited secondary loss.

Phylogenetic systematics of the land snail Basedowena from the Australian arid zone: taxonomic revision with description of new taxa (Stylommatophora : Camaenidae)

The land snail Basedowena Iredale, 1937 currently comprises eight species that inhabit mountain ranges in the central Australian arid zone. By studying the variation in shell and genital anatomy and the differentiation in the mitochondrial markers 16S and COI, we revise the taxonomy of this camaenid and describe new taxa. We demonstrate that the current morphology-based classification has been misled by homoplasy mainly in shell shape. In fact, Basedowena as herein revised contains species with vastly different shells, which have so far been assigned to different genera. By contrast, these species have the same general genital anatomy in common and form a clade in the mitochondrial phylogeny. Based on these findings, we transfer Pleuroxia bethana, P. hinsbyi, P. elfina, P. oligopleura, P. polypleura, P. radiata, Montanomelon angatjana and Minimelon colmani to Basedowena. While Pleuroxia and Montanomelon are maintained as distinct genera, although with fewer species, the monotypic Minimelon becomes a junior synonym of Basedowena. We identify and describe three new Basedowena species (B. bicolor, sp. nov., B. holoserica, sp. nov., B. siparium, sp. nov.). A fourth new species differs substantially from all other arid zone camaenids and is hence placed in a new genus, Xeromelon, gen. nov. The revised delineation of Basedowena renders it now the most widespread camaenid genus in Australia. It is distributed throughout the Australian arid zone from Western Australia, via the Northern Territory and South Australia into New South Wales.

Snails in the desert: Assessing the mitochondrial and morphological diversity and the influence of aestivation behavior on lineage differentiation in the Australian endemic Granulomelon Iredale, 1933 (Stylommatophora: Camaenidae)

Progressive aridification since the mid-Miocene has had a significant influence on the evolution of the biota in the arid zone of central Australia. Especially moisture sensitive groups, such as snails, are often restricted to topographically complex areas, which have acted as refugia in an otherwise inhospitable environment. This historical fragmentation is deemed to be a potent agent of allopatric lineage diversification. Camaenid land snails are amongst only a few terrestrial gastropods that have managed to survive in the arid zone probably due to their ability to escape desiccation through aestivation. Here, we present the first study of the mitochondrial lineage differentiation in an endemic land snail genus from the Australian 'Red Centre', Granulomelon Iredale, 1933. Exposing significant incongruence between mtDNA phylogeny and morphology-based taxonomy, we completely revise the species and genus level taxonomy of this camaenid group. We demonstrate that this genus contains three species, G. grandituberculatum, G. adcockianum and G. squamulosum, which have so far been assigned to different genera: Granulomelon Iredale, 1933 (junior synonym: Baccalena Iredale, 1937), Basedowena Iredale, 1937 and Pleuroxia Ancey, 1887. Two of these species are widespread comprising multiple divergent mitochondrial lineages. Based on a molecular clock estimate, these lineages diverged approximately during the mid-Pleistocene, a period of particularly severe aridification. The phylogeographic patterns are consistent with an isolation-by-distance model in one species but not the other. We suggest that these differences can be attributed to their distinctive aestivation behavior.

A molecular phylogeny of camaenid land snails from north-western Australia unravels widespread homoplasy in morphological characters (Gastropoda, Helicoidea)

North-western Australia harbours more than 300 species of camaenid land snail in 41 genera exhibiting considerable and well documented morphological diversity. We performed Bayesian and Maximum Likelihood analyses of concatenated nuclear (28S) and mitochondrial (COI, 16S) DNA sequences from 140 species of 37 of these genera plus an additional 27 extralimital species in order to resolve their phylogenetic relationships and to address the significance of morphological characters for the delineation of monophyletic taxa. While north-western Australian Camaenidae in their entirety are not monophyletic with respect to extralimital groups, they underwent extensive in situ-diversification in several independent phylogenetic radiations. A Maximum Likelihood-based character history reconstruction revealed extensive convergence in all studied shell characters and in three out of four genital features across this group. However, in some genera close morphological similarity is best explained by the retention of ancestral characters. We hypothesize that both morphological stasis in some groups and convergent character evolution in others can to a large extent be attributed to adaptive transformations in response to historically increasing aridity throughout north-western Australia in concert with structural constraints.

Molecular phylogenetics of the land snail genus Quistrachia (Gastropoda : Camaenidae) in northern Western Australia

Recent collecting in the remote Pilbara region of Western Australia has revealed substantial increases in the apparent distributions of species of the genus Quistrachia, and the discovery of new forms, raising questions about the morphological taxonomy. To resolve these questions, we examined mtDNA sequences in all known species of Quistrachia, the unidentified new forms and other members of the subfamily Sinumeloninae. Phylogenetic analysis confirmed the monophyly of Quistrachia, including one of the new forms. The two other new forms represent new genera within the Sinumeloninae. Monophyly of each species was confirmed, with the exception of Q. legendrei, in which populations from the Dampier Archipelago and those from the adjacent Burrup Peninsula are in separate clades. Based on phylogeny and levels of divergence within other species in the genus, the Burrup populations appear to be conspecific with Q. turneri. This is supported by anatomical comparisons, but not by shell morphology, which may well reflect the evolutionary plasticity of shell form. Given the patchiness of searches for land snails in the largely inaccessible Pilbara region, additional species almost certainly remain to be discovered. Our study shows the value of including molecular analyses in determining the taxonomic status of new forms.

More on snails and islands: molecular systematics and taxonomic revision of Setobaudinia Iredale (Gastropoda : Camaenidae) from the Kimberley, Western Australia, with description of new taxa

Setobaudinia Iredale, 1933 is a genus of camaenid land snails endemic to the Western Australian Kimberley. It comprises 20 currently recognised species, most of which occur within the north-western high precipitation zone between the Admiralty Gulf and Collier Bay and within less than 60 km distance from the coast. Exceptionally, two species are found on isolated limestone outcrops in the drier interior of the Victoria River District, Northern Territory. By studying the differentiation in shell and genital anatomy as well as in the mitochondrial markers 16S and COI, we revise the taxonomy of Setobaudinia and describe new taxa. The Northern Territory species S. victoriana Solem, 1985 is identified as a member of the genus Trachiopsis, which otherwise comprises species from the York Peninsula, Queensland. The species Damochlora spina Solem, 1985 is shown to be a member of the genus Setobaudinia. A new species from the eastern Kimberley has been identified as the sister group of Setobaudinia. It is placed in the new genus Kymatobaudinia for exhibiting morphological characteristics that differ from those of all other Setobaudinia species. In addition, we describe nine new species from coastal areas and islands off the cost throughout the south-west to north-west Kimberley: S. angustilabiata, sp. nov.; S. colmani, sp. nov.; S. incisa, sp. nov.; S. kessneri, sp. nov.; S. latilabiata, sp. nov.; S. longiflagellata, sp. nov.; S. malbyana, sp. nov.; S. minima, sp. nov.; S. plana, sp. nov. ZooBank Publication code: http://zoobank.org/References/3C953F1A-62E5-4CE5-9D5E-D8D5774B4059