Bivalves are some of the most important suspension feeders in aquatic systems. Much research has been conducted on the feeding mechanisms of adult molluscan suspension feeders, but less is known about the feeding mechanisms of their larval stages. To date, the general consensus is that veligers are restricted to collecting particles 4-20 μm in size and that food selection is indiscriminate within this size range, but this hypothesis remains to be directly tested. Therefore, we experimentally assessed this assumption by quantifying microalgal particle capture rates for the larvae of the Pacific oyster (Crassostrea gigas) when fed five different microalgal species individually and in combination. We then tested whether factors such as cell size affected capture rate and consumption, as well as whether capture rate was affected by the presence of other microalgal species. We found evidence of food preference that was not simply a function of size or relative nutritional quality for C. gigas veligers. Further, we found that food selectivity changed through ontogeny. To our knowledge, the changes in selection that we observed through ontogeny have not been previously reported.  https://www.selleckchem.com/products/pd-1-pd-l1-inhibitor-3.html  Interestingly, there was also a sharp decrease in the variability among replicates in consumption rate as the larvae aged. Whether this is a function of velar structure or larval size remains to be tested. Our results suggest some underlying process resulting in certain species of microalgae being captured and consumed at significantly different rates than others.We used three consecutive operant conditioning tasks to determine whether the tropical octopus Abdopus aculeatus is able to learn to recognize a symbolic object, in either real or virtual forms. In Experiment 1, we examined whether octopuses can be conditioned to a real object (a white ball) and whether such trained individuals can select the conditioned object when they are presented with an unconditioned object. We show that octopuses learned to respond to and select the conditioned white ball in preference to the unconditioned object. In Experiment 2, we examined whether octopuses can be conditioned to an object that gradually changes from real to virtual (i.e., an image of that object on a computer screen). We presented four types of objects, all variations of a white ball, in a stepwise sequence as a conditioned stimulus a real white ball, a real image of a white ball without a margin, a real image of a white ball centered within a black margin, and a virtual image of a white ball (a video on a computer screen). Individual octopuses learned to respond to all three real objects, and then a subset of these octopuses responded to the virtual object. In Experiment 3, we examined whether an octopus can learn a virtual image of an object with a specific shape not tested in Experiments 1 and 2. We presented octopuses with an image of a white cross, which was placed at various distances (i.e., close, medium, and far). We found that after having learned these images, octopuses could learn the virtual white cross on a computer screen. Furthermore, when we simultaneously presented octopuses with a conditioned virtual object and an unconditioned virtual object, they selected the former. Through these three experiments, we confirmed that A. aculeatus can learn both real and virtual specific objects.We investigated an unknown ellipsoidal body that is sometimes found in the ovaries of the sea cucumber Apostichopus japonicus. Its external morphology, comprising an ellipsoidal dark central body (about 150 µm in length) and a surrounding transparent layer (about 50 µm in thickness), resembled that of a protozoan cyst, particularly an oocyst. Histological observations of the developing A. japonicus ovaries clarified that a small mass of organisms appeared in the cytoplasm of young oocytes, proliferated in these cells through budding, became rod shaped and arranged radially, and, finally, formed an outer layer. These processes were considered to be the formation of a cyst by a protozoan parasite. The small subunit ribosomal RNA (18S rRNA) gene was amplified from the DNA extracted from unknown ellipsoidal bodies by using polymerase chain reaction with universal primers for eukaryote 18S rRNA. The determined sequence was not identical to any of the known sequences in DNA databases, but it clustered in a clade of coccidian species belonging to Eucoccidiorida in phylogenetic analyses. From these results, we concluded that the unknown ellipsoidal body is a cyst (possibly an oocyst) of a coccidian parasite (order Eucoccidiorida) that is formed in the A. japonicus oocyte, though its lower taxonomic position is uncertain. In a survey of the gonads of wild A. japonicus at Esashi, Hokkaido, during the reproductive season, these cysts were detected in more than 50% of females but were never found in males. We consider that the cysts of this parasite can only be formed in A. japonicus ovaries.Suspension-feeding bivalves are known to discriminate among a complex mixture of particles present in their environments. The exact mechanism that allows bivalves to ingest some particles and reject others as pseudofeces has yet to be fully elucidated. Recent studies have shown that interactions between lectins found in the mucus covering oyster and mussel feeding organs and carbohydrates found on the microalga cell surface play a central role in this selection process. In this study, we evaluated whether these interactions are also involved in food selection in bivalves with other gill architectures, namely, the clam Mercenaria mercenaria and the scallop Argopecten irradians. Statistical methods were used to predict whether given microalgae would be rejected or ingested depending on their cell surface carbohydrate profiles. Eight different microalgae with previously established surface carbohydrate profiles were grown and harvested during their exponential growth phase to be used in feeding experiments. Microalgae were then used in 17 feeding experiments where different pairs of microalgae were presented to clams and scallops to evaluate selection. Decision trees that model selection were then developed for each bivalve. Results showed that microalgae rich in mannose residues were likely to be ingested in both bivalves. N-acetylglucosamine and fucose residues also seem to play a role in food particle choice in scallops and clams, respectively. Overall, this study demonstrates the role of carbohydrate-lectin interactions in particle selection in suspension-feeding bivalves displaying different gill architectures, and it highlights the importance of mannose residues as a cue for the selection of ingested particles.