The genera Mactrella and Mactrinula, both described by Gray in 1853, have generally been considered synonyms. Additionally, five species had been included in Mactrella were later placed in the genus Mactrellona Marks, 1951. The diagnosis of type species of these genera, as well as the study of their type material, have clarified the taxonomic status of the three related genera. The genus Micromactra Dall, 1894, is added to the synonymy of Mactrella. The complete shell morphology of type species Mactrella striatula and Mactrinula plicataria, both introduced by Linnaeus, 1767, is described. An updated synonymy list of each species is provided. In addition, an expanded geographical distribution of the genus Mactrella is given. Illustrations of Mactrellona alata (Spengler, 1802), Mactrellona exoleta (Gray, 1837), Mactrellona clisia (Dall, 1915), Mactrella californica (Conrad, 1837), Harvella elegans (G. B. Sowerby I, 1825), and Mactrella janeiroensis (E. A. Smith, 1915) are included.

Specimens and eggs masses of the gastropod Trochita pileus were collected during a research cruise by bottom trawling at depths between 82 m and 120 m. Adult T. pileus were found attached to such hard substrata as the shells of scallops and oysters. The egg mass of T. pileus is composed of 7–8 transparent, triangular-shaped egg capsules fixed to the substratum with stalks. Four egg masses collected from brooding females, with a total number of 241 embryos, were examined. Trochita pileus is a protandrous hermaphrodite, and histological studies of the male, transitional, and female gonads were performed. The testicular portion of the gonad in both male and transitional individuals and the ovary of the female were studied by histological techniques. Spermatogenesis was observed for males and transitional individuals.

Pomacea canaliculate is a freshwater snail native to subtropical-temperate South America that has invaded several countries around the world. Temperature is probably one of the main limitations to the expansion of this and other apple snails to higher latitudes in invaded regions. Egg masses are aerial, and the duration of embryonic development varies greatly with air temperature. We compared different methods for determining the lower temperature thresholds and the cumulative degree-days (DD) required for the completion of the embryonic development of P. canaliculate. The lower temperature threshold was estimated with four methods: the least standard deviation from the mean of degree-days, the least standard deviation from the mean of days, the coefficient of variation in days and the linear regression coefficient method. The cumulative degree-days were estimated using hourly records and daily averages (calculated according to the single triangle and the single sine methods) of air temperature. The lower temperature thresholds ranged between 15.8°C and 18.3°C and the cumulative DD between 88.8°C.d and 133.8°C.d. The estimations obtained with the single triangle and the single sine methods were exactly the same. The values obtained with the method of the least standard deviation in degree-days and the corresponding cumulative DD were the poorest estimations. The estimates obtained with daily mean temperatures were close to those obtained with hourly records, indicating that recording only maximum and minimum temperatures should be sufficient. The use of degree-day models for egg development in Pomacea will serve to increase the effectiveness and efficacy of control measures targeted to egg masses through a better timing in their application, especially in localities with highly variable temperatures.

The evolutionary processes generating population genetic structures may differ depending on the spatial scale. We examined the population structure of the freshwater snail Radix balthica on a local scale in Saanen Valley, Switzerland. We used a combination of a direct approach by simulating dispersal with parameters gained out of experiments in an artificial pond and indirect molecular genetic approaches by using mitochondrial (COI) and nuclear (microsatellite) marker at all sites harbouring R. balthica in this restricted area.

Contrary to the expectations from the direct methods, populations in homogeneous water bodies were found to be genetically heterogeneous, independently of geographic distance between sites. Instead, several selfing lineages coexisted with little local gene flow among them.

The population structure observed in the valley could thus not be explained by active dispersal alone. It was rather characterized by independent, probably bird-mediated, colonisation events from several sources, in combination with high metapopulation dynamics and a mixed mating system preserving this structure. This population structure has rarely been reported before, but might nevertheless be typical for passively dispersed, patchily distributed taxa (e.g., freshwater invertebrates).

Carditamera bajaensis, new species, is described from semi-infaunal specimens collected in the intertidal zone in the Golfo de California, Baja California Sur, Mexico. The new species resembles Carditamera affinis (G. B. Sowerby I, 1833), the only valid Carditamera species known from within the Golfo de California, with which it has been mistaken, but it differs in shell structure and most conspicuously in life mode — semi-infaunal for C. bajaensis versus byssally attached to hard substrata for C. affinis. Haplotype networks constructed from two mitochondrial genes (16S rRNA and cytochrome b) and one nuclear gene (internal transcribed spacer 2) indicate a clear genetic break between C. affinis and C. bajaensis, as suspected initially due to their different modes of life and shell morphology. This pair of species, C. affinis and C. bajaensis, overlapping in distribution yet genetically distinct, possibly indicate ecological speciation.

Oogenesis of the freshwater mussel Anodonte cygnea was investigated through histological examination over a 12-month period. All specimens were hermaphrodites, having gonads made up of numerous separate female and male acini. Female acini included oogonia with oocytes at different stages of development. Immature oocytes were attached to the acinar wall by a stalk, while mature oocytes were free within the acinus lumen. Several male and female acini were connected to a single germinal duct filled with mature germ cells. A maturity gradation scale was developed, which incorporated the characteristics of the acini, germinal epithelium, lumen and connective tissue. Although oogenesis seems to occur throughout the year, this scale has shown that oogenesis peaks during the summer months.

This study followed the typical and atypical pathways of spermatogenesis in Venustaconcha ellipsiformis (Conrad, 1836) (Bivalvia: Unionoida: Unionidae), during an entire year and documents the developmental stages of both using light and transmission electron microscopy. The spermatozoa produced by both pathways were essentially morphologically identical and contained a single acrosomal vesicle. Production of spermatozoa in the two pathways overlapped from May to October, and vitellogenic eggs were present over this same time period. Atypical spermatogenesis also occurred from November through April. The typical pathway involved the mitotic and meiotic divisions that include spermatogonial cells, primary and secondary spermatocytes, spermatids and mature spermatozoa. In contrast, atypical spermatozoa appeared to be produced in a pathway that included spermatozoa morulae and spermatids produced from spermatogonial cells located in Sertoli cells. Large amorphous inclusions (Al) observed in Sertoli cells, and apparently acting as secondary lysosomes in digesting morulae, are described for the first time. The morphology of the Al was variable, with the Al sometimes containing structures that were organelle-like in appearance and some of the Al appeared to merge together. Phagocytes associated with both the typical and atypical pathways, but distinct from Sertoli cells, were observed clearing the acini of cellular debris. Immunoelectron microscopy detected the presence of both female-transmitted (F) and male-transmitted (M) mitochondria in the spermatozoa present in July (when fertilization takes place). We propose that the necessity of producing spermatozoa with F and M mt genome-bearing mitochondria, to maintain dioecy and 50 : 50 sex ratios in freshwater bivalve populations, accounts for the > 200 million year maintenance of two spermatogenic pathways in the Unionoida.

The malacological works of Sylvanus Hanley (and his relative Charles Thorpe) are discussed and their dates in some cases clarified. The taxa that first appear in these works are listed, their type specimens noted when known, and the current status of the available taxa discussed. Of the 375 species-group names that first appear in these works, 367 are available, and 8 are nomina nude. Of the 367 available species-group taxa, approximately 219 are now considered valid. Approximately 60% of the available species are represented by type material, mainly in the Natural History Museum in London and in the Leeds City Museum in Leeds, U.K. Hanley also described several genus-group and family-group names, some of which are still considered valid.