Winston F. Ponder

The Global Decline of Nonmarine Mollusks

Abstract Invertebrate species represent more than 99% of animal diversity; however, they receive much less publicity and attract disproportionately minor research effort relative to vertebrates. Nonmarine mollusks (i.e., terrestrial and freshwater) are one of the most diverse and imperiled groups of animals, although not many people other than a few specialists who study the group seem to be aware of their plight. Nonmarine mollusks include a number of phylogenetically disparate lineages and species-rich assemblages that represent two molluscan classes, Bivalvia (clams and mussels) and Gastropoda (snails, slugs, and limpets). In this article we provide an overview of global nonmarine molluscan biodiversity and conservation status, including several case studies documenting the diversity and global decline of nonmarine mollusks. We conclude with a discussion of the roles that mollusks and malacologists should play in conservation, including research, conservation management strategies, and education and outreach.

Global diversity of gastropods (Gastropoda; Mollusca) in freshwater

The world’s gastropod fauna from continental waters comprises ∼4,000 valid described species and a minimum of 33–38 independent lineages of Recent Neritimorpha, Caenogastropoda and Heterobranchia (including the Pulmonata). The caenogastropod component dominates in terms of species richness and diversity of morphology, physiology, life and reproductive modes and has produced several highly speciose endemic radiations. Ancient oligotrophic lakes (e.g., Baikal, Ohrid, Tanganyika) are key hotspots of gastropod diversity; also noteworthy are a number of lower river basins (e.g., Congo, Mekong, Mobile Bay). But unlike many other invertebrates, small streams, springs and groundwater systems have produced the most speciose associations of freshwater gastropods. Despite their ecological importance in many aquatic ecosystems, understanding of even their systematics is discouragingly incomplete. The world’s freshwater gastropod fauna faces unprecedented threats from habitat loss and degradation and introduced fishes and other pests. Unsustainable use of ground water, landscape modification and stock damage are destroying many streams and springs in rural/pastoral areas, and pose the most significant threats to the large diversity of narrow range endemics in springs and ground water. Despite comprising only ∼5% of the world’s gastropod fauna, freshwater gastropods account for ∼20% of recorded mollusc extinctions. However, the status of the great majority of taxa is unknown, a situation that is exacerbated by a lack of experts and critical baseline data relating to distribution, abundance, basic life history, physiology, morphology and diet. Thus, the already considerable magnitude of extinction and high levels of threat indicated by the IUCN Red List of Threatened Species is certainly a significant underestimate.

Gastropod phylogeny based on six segments from four genes representing coding or non-coding and mitochondrial or nuclear DNA

Significant differences remain between gastropod phylogenetic hypotheses based on morphological and molecular datasets. We collected additional data from three gene segments (28S rDNA expansion region D1 (36 taxa plus two from GenBank), cytochrome c oxidase subunit 1 (35 species plus one from Genbank) and small nuclear RNA U2 (24 species)). These were combined with data available for the same species for histone H3 and two other segments of 28S rDNA. Analyses of these data using cladistic, maximum likelihood or Bayesian methodologies were conducted in an attempt to resolve some of the differences between current hypotheses of gastropod relationships based on morphological and molecular data. The results were of particular interest in four areas. (1) Patellogastropoda in most analyses are included in a derived clade with some Vetigastropoda. In an analysis with Nautilus as the sole outgroup, transversions weighted threefold as costly as transitions and, with third codon position data ignored, Patellogastropoda are excluded from an otherwise monophyletic Gastropoda. (2) Cocculiniformia was never monophyletic in our analyses, although this possibility is not statistically rejected. (3) Nerita, the only representative of Neritopsina in this dataset, is placed anomalously in most analyses, but is, in a few cases, shown as a sister-group to the Apogastropoda, in accord with some morphological hypotheses. (4) Heterobranchia is rarely monophyletic in our analyses owing to the variable placement of the architectonicoid Philippea. This genus, even judged by the high levels of divergence within Heterobranchia, has undergone extreme rates of substitution. The Euthyneura is invariably monophyletic and nearly always included in a clade with the valvatoidean Cornirostra as its sister-group.

The influence of classification on the evolutionary interpretation of structure a re-evaluation of the evolution of the pallial cavity of gastropod molluscs

Abstract The gastropod mantle, or pallial, cavity and its associated structures have served as a phylobase for studies of gastropod relationships for well over 100 years. We review C. M. Yonges model for the evolution of the gastropod pallial cavity published a little more than 50 years ago, as well as its subsequent mutation by other authors. We then use a recently published (Ponder & Lindberg 1997) phylogenetic hypothesis of gastropod relationships to explore character transformations of attributes associated with the pallial cavity. Significant features of the evolution of the gastropod pallial cavity are the reduction or loss of structures (gill, osphradium, hypobranchial gland) and associated neural and reno-vascular systems on the right side of the cavity, and mechanisms for coping with an increase in overall body size in many clades. The loss of pallial cavity structures has occurred independently in several major clades, the patellogastropods, neritopsines, cocculinoideans, and apogastropods, and probably more than once in the vetigastropods. Evolution of the pallial cavity and associated structures is discussed for each of the clades in which largely different solutions are found to enable the achievement of larger body size. A seeming contradiction reduction of gills with increasing respiratory demand due to increasing body size is a feature of the group. We also examine possible linkages between the evolution of the pallial cavity and other morphological characters that were not suspect as a prioricorrelates of one another. The uncritical application of a current taxonomy to results obtained from applying the comparative method used to study form and function has been a significant hindrance to our understanding of evolution in the last several decades. C. M. Yonges scenario published in 1947 was close to our phylogenetically based hypothesis. However, when it was later forced into agreement with the dominant classification of the last half-century (Thiele 1929–35), most of the points of agreement between the original scenario of Yonge and our phylogenetic hypothesis vanished, with four separate derivations reduced to a single event. This is an example of a Procrustean evolutionary scenario fitting the data to a classification scheme, with taxonomy rather than phylogeny used as the bed.

New species, anatomy, and systematic position of the hydrothermal vent and hydrocarbon seep gastropod family Provannidae fam.n. (Caenogastropoda)

The anatomy of the hydrothermal vent gastropod Provanna is described. It is shown to be a primitive neotaenioglossan with mainly plesiomorphic features in all systems, including open pallial gonoducts, epiathroid nervous system with accessory pedal ganglia and a circulatory system where a considerable portion of the venous blood from the coelomic spaces enters the pallial skirt. Apomorphic features include the possession of an anterior notch, or short canal in the shell (and mantle edge), an annulated sensory pallial tentacle, paraspermatozoa modificd as nurse cells. multiple seminal receptacles, a posterior bursa copulatrix, and a renal oviduct with three distinct regions. the middle one expanded. Comparisons are madc with Abyssochrysos, a genus assumed to be a relict member of the Loxonematoidea, which appears to be the closest known relative. A new family. Provannidae fam.n., is created and tentatively included in the Loxonematoidea. The following new specics are described: Provanna segonzaci sp.n. (from hydrothermal vents at the Fiji Back Arc), P. laevis sp.n. (from hydrothermal seeps in the Gulf of California), P. sculpta sp.n. and P. admetoides sp.n. (from hydrocarbon seeps in the Gulf of Mexico). New records are added for previously described species of Provanna.

A phylogenetic analysis of rissooidean and cingulopsoidean families (Gastropoda: Caenogastropoda)

The Rissooidea is one of the largest and most diverse molluscan superfamilies, with 23 recognized Recent families including marine, freshwater and terrestrial members. The Cingulopsoidea are a group of three marine families previously included within the Rissooidea. A previous molecular analysis including two rissooideans and one cingulopsoidean, indicated the possibility that the Rissooidea is at least diphyletic. We use new molecular data to investigate the polyphyly of Rissooidea and test the monophyly of Cingulopsoidea with a greatly increased taxon set. This study includes the greatest sampling to date with 43 species of 14 families of Rissooidea and all families of Cingulopsoidea. Bayesian and maximum likelihood analyses of 16S and 28S show that there are two major clades encompassing taxa previously included in Rissooidea. These are the Rissooidea s.s. containing Rissoidae and Barleeiidae and the Truncatelloidea containing Anabathridae, Assimineidae, Falsicingulidae, Truncatellidae, Pomatiopsidae, Hydrobiidae s.l., Hydrococcidae, Stenothyridae, Calopiidae, Clenchiellidae, Caecidae, Tornidae, and Iravadiidae. Rissoidae is not monophyletic, with Lironoba grouping with Emblanda (Emblandidae) and Rissoina forming a separate clade with Barleeiidae. Iravadiidae is not monophyletic, with Nozeba being sister to the Tornidae. Tatea, usually included within Hydrobiidae, is distinct from that family and Nodulus, previously included in Anabathridae, groups with the hydrobiids.

Relationships of Placostylus from Lord Howe Island: an investigation using the mitochondrial cytochrome c oxidase 1 gene

Large (5–9 cm in length) land snails of the genus Placostylus are found in New Caledonia and the Loyalty Islands, northern New Zealand, the Three Kings Islands just north of New Zealand and on Lord Howe Island. Their presence on Lord Howe, an oceanic island less than 6 million years old, has been an intriguing biogeographical question. Maximum parsimony and maximum likelihood analyses using cytochrome c oxidase subunit I sequence data suggest that the Lord Howe Island and mainland New Zealand taxa are sisters, but that the Three Kings taxon is independently derived, possibly from New Caledonian stock. Placostylus colonies throughout the area of the present study are under considerable threat, with many intraspecific forms and some species threatened and some listed as endangered species. The taxonomic and conservation status of the Lord Howe Island populations are discussed.

Australian freshwater assimineids, with a synopsis of the Recent genus-group taxa of the Assimineidae (Mollusca: Caenogastropoda: Rissooidea)

The morphology of the two species of Australian freshwater assimineids is described in detail. A new genus and species of Assimineinae, Aviassiminea palitans, is named from freshwater springs in north Western Australia and the Northern Territory. Austroassiminea letha Solem et al., 1982 from coastal springs in south Western Australia is also described and the original anatomical account is corrected in several important details. This taxon is shown to be a member of the Omphalotropidinae and is the only other non-marine assimineid known from Australia. All of the described assimineid genus-group taxa are listed in an appendix, with an assessment of their status, and their known diagnostic characters.

Three-dimensional reconstruction of the odontophoral cartilages of Caenogastropoda (Mollusca: Gastropoda) using micro-CT: Morphology and phylogenetic significance

Odontophoral cartilages are located in the molluscan buccal mass and support the movement of the radula during feeding. The structural diversity of odontophoral cartilages is currently known only from limited taxa, but this information is important for interpreting phylogeny and for understanding the biomechanical operation of the buccal mass. Caenogastropods exhibit a wide variety of feeding strategies, but there is little comparative information on cartilage morphology within this group. The morphology of caenogastropod odontophoral cartilages is currently known only from dissection and histology, although preliminary results suggest that they may be structurally diverse. A comparative morphological survey of 18 caenogastropods and three noncaenogastropods has been conducted, sampling most major caenogastropod superfamilies. Three‐dimensional models of the odontophoral cartilages were generated using X‐ray microscopy (micro‐CT) and reconstruction by image segmentation. Considerable morphological diversity of the odontophoral cartilages was found within Caenogastropoda, including the presence of thin cartilaginous appendages, asymmetrically overlapping cartilages, and reflexed cartilage margins. Many basal caenogastropod taxa possess previously unidentified cartilaginous support structures below the radula (subradular cartilages), which may be homologous to the dorsal cartilages of other gastropods. As subradular cartilages were absent in carnivorous caenogastropods, adaptation to trophic specialization is likely. However, incongruence with specific feeding strategies or body size suggests that the morphology of odontophoral cartilages is constrained by phylogeny, representing a new source of morphological characters to improve the phylogenetic resolution of this group. J. Morphol. 2009.

Examining the phylogeny of the Australasian Lymnaeidae (Heterobranchia: Pulmonata: Gastropoda) using mitochondrial, nuclear and morphological markers

We examined the species groups relationships of the freshwater snail genus Austropeplea using mitochondrial, nuclear and morphological markers in addition to traditional methods of shell shape analysis. Based primarily on the results of a combined molecular and morphological analysis, samples of the nominal species A. tomentosa form distinct lineages. The New Zealand populations of A. tomentosa are a very distinct lineage from any of the Australian populations attributed to A. tomentosa. Furthermore, within the Australian group, three lineages, south Australia, Tasmania and eastern Australia, appear to have undergone recent and/or rapid speciation events. Samples assigned to A. lessoni were resolved as two distinct lineages, representing the eastern and northern Australian populations. Kutikina hispida was resolved within the Australian A. tomentosa clade. Molecular results for A. viridis suggests that it is also composed of at least two distinct lineages that could be treated as species. Incongruence observed between the single mitochondrial, nuclear and morphological topologies highlight the importance of using a number of different datasets in the delimitation of species-group taxa.