George Morgan Davis was a preeminent American malacologist of the latter twentieth century. Seated in Henry Pilsbry's chair at the Academy of Natural Sciences in Philadelphia, his keen eye for morphological detail, matched only by his extraordinary ability to transmit rigorous scientific observation onto the journal page in word, data table, numerical analysis, and delicately stippled anatomical illustration, exceeded even that of his predecessor Henry Pilsbry. From a firm foundation in the classical school of descriptive biology, Davis became the first American malacologist to apply molecular techniques to address systematic questions in the phylum Mollusca, pioneering immunological, protein electrophoretic, and sequencing technologies throughout his long career. The influence that he wielded to shape and mold our discipline during his 40-year editorship of this journal was exceeded only by Henry Pilsbry's 70-year editorship of The Nautilus. Here we review Davis' distinguished career, his 200 publications, the 46 taxa that he named, and the 11 taxa named in his honor.
Davisassiminea, a new genus of the Assimineidae, is proposed for Rissoa (Cingula) capensis G. B. Sowerby III, 1892 from tidal flats of southeastern South Africa. The new genus is unique for the family in the morphology of the radula and reproductive system, and the absence of distinct omniphoric grooves. A congeneric species, Assiminea globulus Connolly, 1939, was also examined anatomically. Our molecular phylogenetic analysis using two mitochondrial genes and one nuclear gene confirms that these taxa are members of the subfamily Assimineinae. Based on molecular and radular evidence, Microsetia durbanensis Tomlin, 1916 is also a member of the new genus. Uniquely for assimineids, these species live on seagrass in marine habitats.
The genus Potamolithus Pilsbry, 1896 represents a group of freshwater gastropods endemic to southern South America, with 48 described species, and constitutes the sole representative of the family Tateidae in the region. Historically, the taxonomy of the genus was based on shell morphology; however, subsequent studies incorporating anatomical and molecular data have highlighted the limitations in species identification based solely on shell features. Since 2010, the team at the Museo de La Plata has conducted comprehensive studies in the malacological province of the Uruguay River, a region with high molluscan diversity and significant relevance for aquatic biodiversity conservation in Argentina. In this context, Potamolithus davisi n. sp. is described through the analysis of morphological and anatomical characters, as well as mitochondrial COI gene sequencing. The results highlight the need for integrative taxonomic approaches and underscore the importance of the Uruguay River as a key refuge for regional malacological biodiversity. This study contributes to the systematic knowledge and conservation of Potamolithus in South American freshwater ecosystems.
Partulidae, a Pacific Island tree snail family of extreme conservation concern, has been the subject of multiple taxonomic revisions in recent years. In addition to numerous changes at the species level, one new genus ( (Sphendone Slapcinsky & Kraus, 2016) has been proposed and two preexisting taxa ( (Rennellia Clench, 1941 and Palaopartula Pilsbry, 1909) have been elevated to genus level, with all three genera based primarily on qualitative appraisals of traditional morphological (shell and soft parts) characters. The limited phylogenetic analyses inclusive of these three genera provide poor-to-ambivalent support for their respective phylogenetic distinctiveness, in part due to the paucity of available genetic markers, but also due to rooting issues caused by a lack of Partulidae sister lineages. We aimed to address both deficiencies by performing double digested Restriction Associated DNA (ddRADseq) phylogenomic analyses that incorporated putative Partulidae sister lineages in addition to type species of the three new, and three pre-existing ( (Partula Ferussac, 1821; Samoana Pilsbry, 1909; and Eua Pilsbry & C. M. Cooke, 1934), Partulidae genera, along with representative congeners spanning their respective ranges. Among the six pupilloidean outgroup families investigated, our results tentatively placed Valloniidae and Gastrocoptidae as sisters to Partulidae and recovered three robust ingroup clades: ( (Eua ( (Samoana (Samoana, Partula)). Rennellia was firmly nested within the Partula clade (sister to Marianas species) and a paraphyletic Palaopartula/Sphendone n. gen. within the Samoana clade [sister to the Marianas species Samoana fragilis (Ferussac, 1821)]. Because reciprocal monophyly is widely accepted as a minimum prerequisite of generic status, these data compelled us to return to the traditional three-genus model for Partulidae. That redesignation was strongly corroborated by molecular clock divergence time estimates and by the presence of phylogenetic gaps, but less so by crown group definitions or the uniqueness of adaptive zones. It significantly expanded our conception of the genus Samoana in terms of its evolutionary history, species composition and ecological diversity. Our phylogenomic results also provided new insights into the enigmatic biogeography of this family, locating the origins of all three genera within neighboring archipelagos and identifying for the first time a sister species to the fabled Society Islands Partula radiation.
The Hydrobiinae is a monophyletic taxon with similar to 16 recognized species. They are distributed throughout the eastern and western North Atlantic and adjacent seas, with a disjunct occurrence along the South African coast. Although some species and genera are widely distributed, others are endemic. The reasons for these contrasting biogeographic patterns are largely unknown, as is the historical biogeography of most hydrobiine taxa. Therefore, the overall objective of this study is to unravel the biogeographic relationships of the subfamily Hydrobiinae. Specifically, a multilocus phylogenetic reconstruction and a species-level ancestral range estimation were performed. In addition, the South African genus Davishydrobia Wilke, gen. nov., was described. The multilocus phylogenetic analyses revealed eight distinct clades at the genus and 16 putative clades at the species level within the subfamily Hydrobiinae. Estimates of the ancestral range suggest that the (Proto-)Mediterranean region is the most likely area of origin of the Hydrobiinae. From there, members of the subfamily presumably colonized coastal areas of the eastern and western North Atlantic, the Arctic Ocean, and South Africa, as well as continental parts of central Asia.
Fasciolosis is a neglected zoonotic disease caused by trematode parasites of the genus Fasciola Linnaeus, 1758, which affects both humans and livestock. Current knowledge on the taxonomy and relationship between lymnaeid gastropod intermediate hosts and Fasciola in Rwanda is insufficient and the geographic extent of the endemicity and the lymnaeid species and strains involved in disease transmission remain unknown. We used extensive field surveys (131 localities) in major types of freshwater ecosystems in Rwanda to (1) identify lymnaeid snails using a molecular approach, and (2) characterize genetic diversity in relation to ecological conditions of the potential intermediate host snails. The only lymnaeid species that could be morphologically and genetically identified was Radix natalensis (Krauss, 1848), found across a wide range of different natural and non-natural habitats (50 localities). All newly sequenced Radix specimens from Rwanda cluster within the R. natalensis group and, togetherwith R. natalensis from Kenya, Uganda, and Zimbabwe, form a highly supported clade. However, the relationship of this clade to other R. natalensis specimens was unresolved. The statistical parsimony network analysis of the clade resulted in a single networkwith 24 unique haplotypes. The haplotypes of the same habitat type (e.g., lakes, rivers, wetlands, and rice plantations) did not form single clusters within this network. This also applies to the comparison between natural and non-natural habitats. We discuss the biogeographical and parasitological implications and compare the new findings with patterns of other lymnaeid species across Africa. Additionally, we suggest further research involving xenomonitoring and eDNA studies.
This review examines the early contributions of George Morgan Davis (1938-2024) to the systematics and evolution of some freshwater gastropods, with emphasis on cerithioidean taxa, e.g., Brotia H. Adams, 1866 (today considered as Pachychilidae) and Semisulcospira O. Boettger, 1886 (Semisulcospiridae). Building on taxonomic revisions and the pioneering use of electrophoretic data, Davis developed broad hypotheses on speciation (including allopatric versus sympatric origins), radiation, hybridisation, introgression, and historical biogeography that anticipated integrative approaches later formalised in evolutionary systematics. His seminal 1982 review on "adaptive radiation" also addressed fundamental cladistic questions and underscored the necessity of synthesising multiple lines of evidence to resolve species boundaries and diversification processes. His original analyses of endemic radiations of Semisulcospira in Japan, in particular Lake Biwa, and triculine gastropods in the Mekong River, in comparison to other riverine radiations, e.g., of Brotia in the Kaek River in Thailand, highlighted the interplay of extrinsic factors (tectonics, drainage history, ecological complexity) and intrinsic traits (e.g., viviparous strategies, parthenogenesis) in shaping diversification. Although developed with limited phylogenetic and biodiversity data, his multidimensional "phylogenetic topology" can be viewed as an attempt to integrate all available lines of evidence from the various analytical components to unite phylogenetic inference, historical biogeography, and ecological causation based on intrinsic characters. Reconsidered here against modern molecular phylogenetic and genomic insights, Davis' work appears strikingly prescient, foreshadowing current integrative frameworks for systematics, albeit at the same time pointing to the limitations of his early synthesis. By situating Davis' legacy within ongoing debates on species concepts and delimitation, speciation modes, and the role of historical versus ecological drivers, this study underscores how past conceptual advances continue to inform contemporary biodiversity research. Re-evaluating Davis' hypotheses further illustrates how he helped shift malacology beyond pure taxonomy and classification towards truly "evolutionary" systematics that remains central to understanding radiations, not just in freshwater gastropods.
Recently two nonindigenous species of the Bithyniidae were found in freshwater habitats of Honsh & umacr;, Japan. Based on morphological examination and molecular phylogenetic analysis of their mitochondrial DNA, they were identified as Pseudovivipara eximia (Frauenfeld, 1864) and Parafossarulus longicornis (Benson, 1842), both of which are known to be distributed mainly in China. These species are anatomically similar to each other and included in a clade Annandale in Annandale & Prashad, 1924, was confirmed to be a junior synonym of Pseudovivipara Annandale, 1918. In Japan, introduced populations of Pseudovivipara eximia have been recorded from five prefectures (Aomori, Niigata, Ibaraki, Chiba, and Shiga) in northern to central Honsh & umacr;, and Pseudovivipara longicornis is established only in Lake Kawaguchi, Yamanashi Prefecture. Middle Pleistocene fossils of Pseudovivipara longicornis have been reported around Lake Biwa in Shiga Prefecture, indicating that this species was previously found in Japan, but later became extinct, perhaps in the upper Pleistocene.
Oncomelania hupensis iriomotensis Fukuda & Sawada, n. ssp., is described from around waterfalls on Iriomote Island at the southwestern part of the Ry & umacr;ky & umacr; Archipelago, Okinawa, Japan. The subspecies has an extremely short sperm duct similar to that of O. h. nosophora (Robson, 1915) from mainland Japan, but the shell is ovate and readily distinguishable from the latter. According to the mitochondrial phylogeny, the subspecies is included within a clade of O. hupensis Gredler, 1881 and its subspecies. It is known only from very narrow ranges in two localities and can be evaluated as critically endangered (CR) according to the criteria for the Red List by the Japanese government. DNA from Schistosoma japonicum (Katsurada, 1904), which uses O. h. nosophora as an intermediate host, was not detected in environmental DNA analyses of the snail habitats on Iriomote Island. In addition, cercarial shedding was not observed in infection experiments. However, although no data in our study suggest a potential infection risk, further research is required to evaluate the potential risk of schistosomiasis.
We update the distribution of two slug species Arion fuscus M & uuml;ller, 1774 and A. subfuscus Draparnaud, 1805 in the Upper Great Lakes Region of the United States using molecular identification methods. These slugs are invasive in North America, and they are cryptic in terms of their morphological identification. Arion fuscus has not previously been reported in the literature in the Upper Great Lakes area, and A. subfuscus has previously been reported as abundant in this region. However, all previous distribution studies were determined using visual identification tools, which can result in misidentification between cryptic species. To reassess the distributions of these species, we used a mitochondrial ribosomal subunit 16S PCR amplification coupled with either DNA sequencing or a restriction enzyme digest assay to distinguish slug specimens that were morphologically consistent with both A. fuscus and A. subfuscus. We additionally identified any other slug species that were found along with the A. fuscus complex specimens, either through morphological characteristics or DNA sequencing. We collected slugs in 11 locations around Lake Superior, Lake Michigan, and Lake Huron using beer-baited pitfall traps from May to September 2022 and at one location from October to December 2023. We collected slugs in Marquette, Michigan, biweekly, a total of eight times, throughout the summer of 2022 to monitor change in slug activity over time. We found A. fuscus at nine of the 11 sampling locations and A. subfuscus at one location. Arion fuscus was found early in the spring before other slug species were active, and into late fall and early winter on days above freezing. The paucity of records of A. subfuscus and ubiquity of A. fuscus suggests that previous reports of A. subfuscus based on visual identification were potentially incorrect and suggests that molecular confirmation or dissections of reproductive anatomy are critical for accurate understanding of species distributions.
Since the pioneering immunological work of Davis & Fuller (1981), molecular data have become a major tool in research on Unionida. Mitochondrial DNA has been especially widely used. We examine the current state of available data and areas needing more research. Phylogenetic analyses suggest further taxonomic revisions. Mitogenomic and nuclear genomic sequencing will continue to grow in importance, but the individual mitochondrial gene sequences will remain important for many applications.
Freshwater mussels play vital roles in ecosystems by providing services that improve water quality, sequester harmful substances, cycle nutrients, and serve as food for animals; however, many mussel species are rapidly declining and several species are at risk of extinction. Challenges in finding and assessing mussel populations have hindered collecting basic information, e.g., age structure, size distribution, and habitat preferences, which ultimately reduces effective management strategies. Our study assessed the length-age relationship and calculated growth rates of the Western Pearlshell-Margaritifera falcata (A. Gould, 1850)-and the California Floater-Anodonta californiensis I. Lea, 1852-in western Wyoming, U.S.A. We collected deceased mussel shells along the Bear River and measured shell length, width, age, and distance between annuli. We developed a new method of aging thin-shelled mussels using transmitted light. The oldest California Floater was 12 yr, and plots of length by age exhibited linear growth whereas width of annuli showed logarithmic growth. Both methods displayed logarithmic growth for the Western Pearlshell, and the oldest individual was 60 yr. We calculated the age of live mussels measured in the field based on our relationships; however, growth and size can differ among regions due to differences in habitats, and we suggest creating relationships for each population. Our study contributed basic data about two declining western mussel species providing information to assess populations and inform management strategies to mitigate threats.
Additional material of previously described species attributed to Margarites J. E. Gray, 1847 and Falsimargarita A. W. B. Powell, 1951 from Brazil was examined using detailed anatomical data and constructing a morphological phylogeny. The new analysis revealed that these taxa are more closely related to the Calliostomatidae and should be placed in the new genus Vaninia, with the type species Margarites imperialis Simone & Birman, 2006. The following new combinations and species are proposed: Vaninia dnophera (Watson, 1879) comb. nov.; Vaninia mirabilis (Simone & Birman, 2006) comb. nov.; and Vaninia vanini gen. nov. sp. nov. The placement of Vaninia gen. nov. as a calliostomatid is supported mainly by radular synapomorphies, including the presence of long, delicate, serrated rachidian teeth and an enlarged innermost pair of marginal teeth. Vaninia gen. nov. differs from other calliostomatid genera primarily by its thinner shell lacking strong color and pattern, a protoconch without a honeycomb pattern, the absence of a pseudoproboscis, no intestinal loop inside of the hemocoel, and the presence of a brood pouch in the right kidney.
Until now, an exhaustive list of Panamanian heterobranch sea slugs (Mollusca: Gastropoda) had not been made. Here, we present a descriptive list of all species of sea slugs off of the coasts of Panam & aacute;, based on published references and confirmed photographs of collected species. All publications referring to collections of these gastropods were compiled and examined, and specimens were collected from different coastal areas of Panam & aacute;. The resulting catalog contains 232 species of heterobranch sea slugs, of which 117 are found on the Caribbean coast and 127 are found on the Pacific coast. Eight species have a bicoastal distribution, and 18 species have an amphi-Atlantic distribution. This study confirms the high biodiversity of heterobranch sea slugs inhabiting the Panamanian coasts. However, because the Pacific coast has been less well studied, future research should include more extensive sampling in these locations.
Episodic mortalities in October 1985 and December 2023 are recorded for mollusks and other organisms on intertidal platforms in the Perth metropolitan region of Western Australia (WA) during periods of elevated air temperatures that coincided with lunar low spring tides. This was similar to mortalities previously reported for the western end of Rottnest Island, offshore from Perth, and are natural occurrences. Mollusks on the Rottnest platforms decreased substantially in both diversity and density between 2007 and 2021. This was thought to be due to a severe marine heatwave along the WA western coast in 2011 caused by global warming, unlike the mortalities observed during this study in 1985 and 2023, which were caused by a combination of high air temperatures and low spring tides. Because marine heatwaves are increasing in frequency and intensity, it is importantto distinguish their impacts from previously occurring natural events associated with high air temperatures coinciding with low spring tides.
Although the life history of the invasive terrestrial slug Arion vulgaris Moquin-Tandon, 1855 has been well studied, there are no long-term studies on the variation in its abundance. In 2003-2022, we used plasticine baits to monitor annual fluctuations in the abundance of a local Arion vulgaris population in Central Europe and studied the factors that influence these fluctuations. The consumption of plasticine, which is a reliable proxy of the abundance of slugs, varied between different years by a factor of 43. The maximum intensity of consumption occurred in July. The variability in slug abundance, as estimated from plasticine bait consumption, was irregular across years. Oviposition took place from September-November. The number of eggs laid did not limit the abundance of the filial generation. Slugs spent the winter period in the egg stage (similar to 25% of the population) or as juveniles, whose winter mortality varied from 18-100% among years. Winter temperatures were not a significant predictor of slug abundance in the following season, whereas the weather in spring and early summer determined the abundance. Amount of precipitation in April and May had a positive effect (P = 0.01). In contrast, the number of days from April-July in which minimum temperature at a depth of 2 cm below the surface exceeded 18 degrees C (i.e., the optimum temperature for slug development) had a negative effect (P = 0.045). These two factors combined explained 55% of the interannual variability in slug abundance (r = 0.74). The robustness of these resultswas backed up by the data from a spatially isolated nearby population, showing similar patterns of annual changes in abundance.
In a recent phylogenetic study of Mesoamerican freshwater mussels (Bivalvia: Unionidae), new molecular support for the tribe Popenaiadini was presented. Several genera of Mesoamerican mussels, including Nephronaias Crosse & Fischer, 1894, were predicted to be within the Popenaiadini tribe based on morphology, but this hypothesis had not been tested with molecular data. Several freshwater mussel specimens were recently collected in Guanacaste Province, Costa Rica. Based on the morphology of the specimens, the known distribution of Nephronaias in Costa Rica, and examination of specimens in the Zoology Museum of the University of Costa Rica, this species was identified as Nephronaias tempisquensis Pilsbry, 1920. After amplifying a gene extension characteristic of the male-transmitted genomes of freshwater-mussel species exhibiting doubly uniparental inheritance (DUI) of mitochondrial DNA, it was concluded that N. tempisquensis exhibits DUI. Phylogenetic analyses of a combination of male-and female-transmitted mtDNA gene sequences and one nuclear gene region are consistent with the hypothesis that N. tempisquensis is a member of the Popenaiadini tribe and is closely related to the Mesoamerican Psoronaias/Psorula species complex. In addition to providing novel sex-related mtDNA data, the current study presents the first DNA sequence data for the genus Nephronaias and among the first molecular data published for native freshwater mussels from Costa Rica.
A review of valid species within genus Pygmaeconus Puillandre & Tenorio, 2017, is presented. Combined analysis of molecular [partial mitochondrial cytochrome c oxidase subunit I (cox1) gene sequences of several individuals, and a nearly-complete mitogenome for one individual] and morphological (shell and radulartooth) characters revealed thattiny cone snails collected with algae and shell grit by scuba at 12 m depth in the southeastern Philippines correspond to a new species, introduced here under the name Pygmaeconus atomus sp. nov. It attains a maximum adult size of < 5 mm, being arguably the smallest recorded member of the cone-snail fauna worldwide.
Alan Kohn was a remarkable malacologist with a diversity of research interests that extended beyond the study of the Conidae (Gastropoda) to a wide range of mollusks, other marine invertebrates, and the history of biology. He mentored several generations of undergraduate and graduate students, post-doctoral fellows, and junior colleagues, encouraging them to go beyond what they thought they could do, and supporting them wherever their careers took them. He also taught hundreds of students over nearly four decades, including the signature Invertebrate Zoology course at the University of Washington, both on the main campus and at the Friday Harbor Laboratories. He also was an instructor in the courses of the Tropical Marine Mollusc Programme (Thailand) and the National Workshop on Marine Molluscs (Vietnam). Kohn was active in several scientific societies, serving as President of the American Malacological Union, Pacific Division; President of the American Malacological Union; and President of the Society of Integrative and Comparative Biology. His publications focused on the ecology, systematics, and biogeography of the Conidae, using the species of that family as model organisms to provide broader insights for the study of marine life and to address key ecological and biogeographical questions. He wrote numerous book reviews that were not only informative but also helped broaden his perspective across biology and paleontology.
Nearly 70 years ago, the fish-hunting strategy of the marine gastropod snail Conus striatus Linnaeus, 1758, was unveiled for the first time. Now, Conus striatus is one of the most recognizable and most studied conids, and some toxins (conotoxins) have been characterized from its venom. In his pioneering work, Alan Kohn showed that upon injection of venom through a harpoon-like modified radular tooth, the fish prey of Conus striatus is rapidly immobilized, within a few hundred milliseconds to a couple of seconds. The cocktail of conotoxins induces strong tetanic contractions of all muscles, with visible fasciculation (twitching) of the fish's fins. In this review, we wish to honor the memory of Alan Kohn by summarizing the current knowledge of the venom composition and biological activity of conotoxins of Conus striatus. From the 103 entries of conotoxins from Conus striatus that occur in the Conoserver database, 74 are mature conotoxin sequences and only a dozen or so have been pharmacologically characterized. Surprisingly, the major toxin class responsible for the "taser-like" effect in fish originally observed, the kappa A-conotoxins, remains poorly understood. Only one three-dimensional structure is known, and the molecular target and mode of action are at best uncertain. This clearly highlights that, despite the vast amount of data accumulated over the years, even for such heavily investigated species as Conus striatus, many important questions remain.
