Two new species, Silicula beringiana and S. okutanii, are described from the northwestern Pacific. These species have an elongate shell with extended and tapered posterior end, differing from each other in form and proportions. Silicula beringiana was found in the Bering Sea, Kamtchatky Strait, and near the southeastern coast of Kamchatka (Pacific Ocean) at 489–4,984 m depth. Silicula okutanii was found in the Pacific Ocean at a latitude of the northern part of Japan at 5,219–5,352 m depth. Silicula sandersi (Bernard, 1989) and Propeleda soyomaruae (Okutani, 1962) were re-examined. Based on comparison with the description, pictures and photos of the type species of Silicula Jeffreys, 1879, Lamellileda Cotton, 1930, Poroleda Hutton, 1893, and Propeleda Iredale, 1924, the following combinations are suggested: Lamellileda sandersi Bernard, 1989, and L. soyomaruae (Okutani, 1962).

The taxonomy and anatomy of the southwestern Atlantic geoduck, Panopea abbreviata Valenciennes, 1839, are revised. Materials from several institutions, as well as new living specimens collected from the coast of Argentina were studied. Type materials of all related nominal species are illustrated. The shell morphology, shell ultrastructure, hinge, ligament and mantle cavity organs are described. The symbiotic relationship with the nemertean Malacobdella arrokeana, attached to host mantle tissues, is mentioned. Panopea abbreviata is abundant in the gulfs of northern Patagonia. It occurs in the subtidal zone from 8 to 25 meters deep, deeply buried in the sediment. It has a large thick shell, shortener at the posterior end, with exposed siphons covered by a dark brownish periostracum; a hinge plate characterized by a single cardinal tooth in each valve; and shell ultrastructure with three layers: an outer layer of nearly vertical and composite prisms, a middle, true homogeneous layer, and an inner layer of alternating sublayers of fine complex crossed lamellar and irregular simple prisms. The fused mantle is only interrupted in the pedal gape. Ctenidia and labial palps association belongs to the Category III and ctenidia type C(1). Panopea antarctica is its only synonym. The fossil taxa Panopea truncata, P. inferior, P. hauthali, P. coquimbensis and P. guayacanensis are excluded from the synonymy.

Thersites mitchellae (Cox, 1864) (Camaenidae) is a regionally endemic Australian land snail that is critically endangered under the Commonwealth Environment Protection and Biodiversity Conservation Act 1999 (EPBC Act). We studied its habitat use and movement patterns. Knowledge of habitat use is relevant to the conservation of the species, and knowledge of movements is relevant to the interpretation of the results of capture-recapture studies and occupancy-based habitat models. We provide quantitative data of nightly distances travelled, the probability of moving on a night, retreat site selection, overnight substrate use and activity. A total of 636 location positions for 11 snails was recorded on 12 nights over an 18-day period. Nocturnal movements measured at approximately 2-hour intervals showed that the mean nightly movement was 457.8 cm. The maximum nightly movement by an individual was 1,575 cm, and the maximum nightly displacement was 1,270 cm. Over the study period, the maximum movement from capture was 74.45 m, and the maximum displacement was 31.80 m. The results show that the probability of moving on a night, and the nightly distance moved once active both increase with increasing humidity up to a maximum and then decline. Whilst individuals did not return to the same retreat site location with any reliability, there is evidence of active and frequent selection of particular retreat site types within selected habitats. Snails most frequently selected sedge retreat in rainforest (66.7%) and in paperbark wetland (59.3%), and despite the scarcity of sedge in palm forest, it was the most frequented retreat site group overall (42.5%). Snails selected palm frond retreats most frequently in the palm forest (66.7%), and coarse woody debris (CWD) was selected in all habitats (17.9%) and most frequently in the palm forest (27.8%). Statistical analysis revealed significant variation among individuals in their relative use of retreat site types, and significant association between the selection of retreat site types and the initial habitat in which the individuals were located.

“Calliostoma” blakei Clench & Aguayo, 1938, described from Río Negro Province, Argentina, appears in the literature either under the genera Calliostoma, Photinula (Calliostomatidae) or as a member of the Umboniinae (Trochidae). The study of live-collected specimens allows to revise its generic placement.The species is characterized by a bipectinate ctenidium with short afferent membrane, isolated appendices in the left side of the neck, and the rachidian and the first lateral teeth reduced to their base. This set of characters, not present in any other trochoid, leads us to propose the new genus Carolesia for this species.

Pomacea canaliculata is a South American apple snail that shows a multiple mating behavior. The copulations are frequent and long lasting, and consequently the males have to face strong sperm competition. The outer gland at the base of the penis sheath secrets drops of mucus that females eat during copulation. These mucus drops are nuptial gifts, and the occurrence of them is the only known instance of this behavior in molluscs. We investigated three possible functions of the gift-giving behavior in P. canaliculata based on three hypotheses: prowler deterrence, male mating effort and paternal investment. We also quantified the frequency of nuptial gifts in two populations of P. canaliculata and its possible role in male competition. We found no aversive reaction neither in females nor in males, but females were attracted to the mucus secretion. The consumption of artificial nuptial gifts (homogenates of the outer sheath gland) had no effect on the copulation duration nor on the total number of eggs and egg masses laid by females. In the field, the frequency of nuptial gifts was almost ten times greater in the population with the highest density of snails, indicating a much higher rate of production of nuptial gifts. The proportion of couples with both nuptial gifts and a prowler males attached was significantly higher than expected by chance in the population with the highest population density. Even though our results give no support for the three hypothesized functions for the nuptial gifts in P. canaliculata, this study revealed a possible different role in male competition: the enticement of the female to remain in copulation when the other males are trying to gain access.

The ultrastructural features of the spermatogenic development and mature spermatozoa morphology of Atrina maura were investigated through transmission electron microscopy. The testis displays a diffuse tubular structure in which gametes develop within a concentric arrangement according to the degree of development. Within the tubules also appear Sertoli cells, which contain a large amount of lipid droplets and glycogen granules in the cytoplasm, suggesting a nutritive role in the first spermatogenesis stage (spermatogonia). Four gamete maturation stages co-occurred in the same individual: spermatogonia (4–8 μm), spermatocytes (3–4 μm) (including primary and secondary), spermatids (2.5 μm) and spermatozoa (∼ 2 μm head length). The proacrosomal vesicle and flagellum occur only until the first stages of spermiogenesis, contrasting with the early formation of both structures in spermatogonia and spermatocytes in other bivalves. In A. maura, the material in the acrosomal vesicle of mature spermatozoa shows a characteristic electron density pattern, which seems to be an exclusive taxonomic feature of the family Pinnidae. However, A. maura displayed only four mitochondria in the midpiece, contrasting with five in all other species in this family.

Pomacea canaliculata is a freshwater gastropod native to southern South America and is listed among the world's 100 worst invaders. Diverse food sources can be exploited by this apple snail, including snails with gelatinous and subaquatic egg masses. Records of ingestion of their own egg masses (egg cannibalism), which are aerial and calcareous, have only been anecdotal in P. canaliculata. Our aims were to study egg cannibalism in a natural population and also under laboratory conditions. In a stream population from the southern Pampas, we recorded P. canaliculata attacking their own fresh egg masses, which had been naturally submerged by an increase in water level. In addition, when we artificially submerged fresh and old egg masses in a field experiment, we observed several snails readily attacking both. In the laboratory, we also observed the capture by pedal surface collecting of floating remains of egg masses. In laboratory trials, juveniles fed on eggs reached larger sizes than starved snails but smaller than those fed on lettuce; adult snails also eat eggs, but their growth rates were not affected by the food regime. Pomacea canaliculata eggs present defensive and anti-nutritive compounds that apparently dissuade almost all potential predators, but this snail did not appear to be negatively affected when feeds on its own eggs. The ingestion of egg remains and submerged egg masses is probably more frequent than previously considered in P. canaliculata, which may take advantage of using these alternative food resources when others are scarce.

The present study analyzed growth and longevity of the endemic cave dwelling bivalve Congeria kusceri obtained from the pit Jama u Predolcu, Croatia. A water temperature of 13–14°C constituted the lower limit for shell growth of C. kusceri. Obtained data also indicated that enhanced calcium uptake by C. kusceri during its summer growth and reproductive phases coincided with a decrease in alkalinity of the pit water. An analysis of shell growth rings in C. kusceri has identified an impressive longevity of 53 years. Calculations of growth rate suggested maximum theoretical shell lengths (L∞) of 16.7 mm for males and 18.7 mm for females and a growth constant of 0.04 year^-1 for both sexes. Congeria kusceri can, however, grow to a shell length of > 24 mm, suggesting that longevity of this species could be greater than that identified in this study. The obtained results add to our understanding of how colonisation and continued and successful occupation of a subterranean freshwater habitat has been achieved.

To obtain more data about the digestive system of cephalaspideans, the esophagus and crop of Aglaja tricolorata were investigated using light and electron microscopy. In this cephalaspidean, the low epithelial cells of the anterior esophagus have a border of microvilli covered by a cuticle formed by acid polysaccharides. The esophageal pouches at the hind region of the anterior esophagus contain subepithelial secretory cells filled with electron-dense vesicles rich in neutral polysaccharides and proteins. A ciliated epithelium covers the base of the esophageal pouches. In the crop, the tall columnar epithelium is covered by a cuticle and forms many deep invaginations. The cuticle on the surface of the epithelium contains acid polysaccharides, but the material filling the lumen of the epithelial invaginations consists of neutral polysaccharides and proteins. Epithelial cells of the crop have a border of short microvilli and many mitochondria; lysosome-like bodies and some lipid droplets are present in the apical region. The elongated nucleus, numerous deep cell membrane invaginations and several hemidesmosomes are located at the basal region. Secretory cells are absent in the crop. Numerous large vacuolar cells are present in the connective tissue of the crop. With the pyroantimonate method, calcium was detected in the peripheral vesicles and central vacuole of these cells. WDS X-ray Intensity maps obtained by EPMA (Electron microprobe) confirmed the presence of calcium. This result supports the relationship between the vacuolar cells of aglajids and the calcium cells of pulmonate gastropods. In the posterior esophagus, epithelial cells are similar to the epithelial cells of the crop and secretory cells are also absent.

This project was conducted to determine if chromosomal characteristics can provide information useful in systematics of the naiades (Bivalvia: Unionida). A field-compatible slide preparation technique was perfected to the point that a few chromosome spreads could be expected from most processed animals. Chromosome slides were prepared from 250 naiades collected in ten of the east-central and southeastern United States, the western state of Oregon, and Manitoba Province, Canada.

The 65 species of North American naiades for which chromosome numbers were determined during this project (64 members of the family Unionidae and one member of the family Margaritiferidae) all have a diploid number of 38 chromosomes. This number is identical to reported diploid numbers for the 11 European and seven of the eight Asian unionid and margaritiferid species that have been studied, strongly suggesting that 38 is the diploid number present in the largely Northern Hemisphere superfamily Unionoidea. In the other unionid superfamily, the Etherioidea, the three Australian and one South American hyriid naiades that have been studied all have 34 diploid chromosomes, while the single studied African iridinid species has 20 chromosomes. If this difference in chromosome numbers is substantiated as more, especially Southern Hemisphere species are studied, this straight-forward morphologic character could become important in recognizing distinctions between high-level groups of naiades.

An analysis of chromosomal morphology focused on two metrics: Arm Ratio (r) and Relative Length (RL). When considered together, these two virtually independent metrics sort the chromosomes into similar-size and similar-shape groups that can facilitate comparisons between species. Analysis of the suggested karyotypes for these two metrics and the detailed karyotypes of their interaction demonstrates the similarity of two species in the same naiad genus and the substantial dissimilarity of two species in different naiad tribes. Analysis of the r and RL metrics for ten species and an all-inclusive composite demonstrates that karyotypic data can recognize similarities and differences among naiad species that correspond with results from other morphologic and genetic character sets.