Balea

Abstract: The genus Tristania Boettger, supposedly endemic to islands in the Tristan da Cunha-Gough group in the South Atlantic, is shown to be congeneric with Balea from the Palaearctic. Consequently, the subfamily Tristaniinae, recently erected to accommodate Tristania, becomes invalid and should be synonymized with the Baleinae. Austrobalea, the only member of the Clausiliidae known from southern Africa, exhibits similarities in shell form to Balea, but is shown to belong to the Mentissoideinae. Following a review by Odhner (1960), six species of Tristania (now Balea) had previously been described from the four islands in the Tristan-Gough group. We disagree with some of Odhner’s conclusions. For example, we believe that the type of ventricosa from Tristan is specifically distinct from the form with a large, broad shell and pronounced spiral sculpture that occurs on Inaccessible and possibly Nightingale, which we here describe as a new species (Balea holdgatei). An additional undescribed species (B. swalesi) with a ribbed shell and distinctly flattened whorls is also described from Inaccessible. The status of B. costigera, known only from juvenile shells with strong ribbing, requires clarification, as does that of B. levior, previously described as a form of ventricosa. Anatomical descriptions are provided for seven of the nine species of Balea now known from these islands. Details are given of their occurrence on each island, together with their habitat preferences. Apart from B. swalesi, and the poorly understood B. costigera and B. levior, all the species occur on more than one island, where it is common for up to three (rarely four) species to occur microsympatrically in any one habitat. Balea tristensis is the most ubiquitous and variable species, occurring in every major habitat on each of the four islands. On Gough it was the only species to extend upwards into the montane moorland, whereas on Inaccessible it even lived in dried holdfasts attached to the upper part of the boulder beach, a novel habitat for any clausiliid. Balea costellata also has broad preferences, but is absent from montane moorland and coastal tussock grassland. Other species showed more definite habitat preferences: B. ventricosa on branches and under loose bark of Phylica arborea; B. goughensis and B. flavida in Spartina arundinacea tussock; B. holdgatei and B. swalesi in fern-bush.

Abstract: Land gastropod fauna of the valley of Pieninski Potok, tributary to the Dunajec River, was studied qualitatively and quantitatively in 1995-1998. Among plant communities Carpathian beech forest dominates. Forty nine species (42 in quantitative samples) of 16 families were recorded, Clausiliidae, Zonitidae and Helicidae being the most numerously represented. The density ranged from 106 to 253 individuals per m 2 , the dominants being Vestia gulo (Bielz), Macrogastra ventricosa (Drap.), subdominants Balea biplicata (Mont.) and Vitrea diaphana (Studer); dominants among litter species being Vitrea diaphana, Aegopinella pura (Alder) and Carychium tridentatum (Risso). These species are the most typical and indicative of the malacocenosis of the Carpathian beech forest. The malacocenosis is multicomponent, polymictic (TDI = 0.93). Simpson's diversity index is high (I = 0.065).

Abstract: Eight German populations of the land snail Balea biplicata (Mollusca: Clausiliidae) were studied using the randomly amplified polymorphic DNA-polymerase chain reaction and morphometrics (principal component and discriminant analysis) to examine population structure and gene flow patterns in a fragmented landscape mosaic along the Elster/Saale riparian system, Germany. A variety of population genetic analyses targeting either more on the geographic scale of gene flow (genetic distances, F statistics, Mantel test) or on local genotypic structure (heterozygosity, linkage disequilibrium, bottleneck probability) showed that (1) the population system in total is governed by high gene flow independent of geographic distance, (2) genetic structure on the narrower sampling scale is mainly determined by stochastic processes due to genetic drift in small isolated and frequently recolonized populations, and (3) the morphometrical variation of the populations was related neither to habitat nor to genetic heterogeneity. The potentials for active and passive dispersal capacity of the snails and possible environmental impacts on their population structure are discussed.

Abstract: Balea fallax (Rossm.) collected from the Roztocze Upland (SE. Poland) was kept in the laboratory for four years. Observations were conducted between March and October when the snails were kept at room temperature (18–25°C); in winter they were stored at 3°C. The egg-laying period started in late March and lasted till October, with maxima in spring and early autumn. The snails laid oval, gelatinous eggs with separate calcium carbonate crystals in the external envelope (average egg size 1.96 × 1.73 mm). The eggs were deposited in batches (up to 14 eggs at a time) or singly. The number of batches per snail per year ranged between 1 and 4. Snails isolated before maturation laid defective eggs which failed to develop, which suggest that the species is incapable of uniparental reproduction or at least the ability is very limited. The reproduction rate decreased during consecutive years, probably as a result of the aging or the shortage of allosperm in isolated individuals. Compared to batches of typically oviparous clausiliids, eggs of B. fallax hatched slightly earlier (interval between oviposition and hatching lasted 8–10 days at room temperature). It is likely that the adults retained developing eggs in the uterus for a short time. The juveniles needed at least 6 months to attain the ultimate shell size.