Anatomy of the pallial tentacular organs of the scallop Nodipecten nodosus (Linnaeus, 1758) (Bivalvia: Pectinidae)

Toxic effects of atrazine on freshwater mussels (Elliptio complanata)

Atrazine (ATR) is a commonly found herbicide contaminant in water bodies across the United States. In this study, native freshwater mussels (Elliptio complanata) were investigated to determine histopathological effects and bioaccumulation of ATR under laboratory conditions. Mussels were collected from the Rice Creek Field Station, Oswego, NY, and were exposed to two different concentrations of ATR (15 and 150 μg/L) for 4 weeks. Histopathological phenotypes induced by ATR include reduced or no ciliary epithelium, ciliary cells merged or completely absent, skeletal rods and connective tissue reduced, causing malformed gill filaments; inhibition of condensation of spermatogenic cells and induced necrosis in spermatocytes in testis; disintegration of acini, oocytes, follicles, and epithelium of the duct, disintegration of the yolk and stalk connecting acini to the follicular wall in ovaries. There were no apparent ATR-mediated histopathological effects in the mantle tissue. Liquid chromatography-mass spectrometry was used to quantify the levels of bioaccumulation of ATR in the tissues where the teratogenic effects are observed from the histological analysis. Bioaccumulation of ATR was observed in gills (0.11 µg/g in the ATR 15 µg/L group and 0.51 µg/g in the ATR 150 µg/L group) and visceral tissues (0.11 µg/g in the ATR 15 µg/L group and 0.63 µg/g in the ATR 150 µg/L), correlating with the histopathological phenotypes. ATR's action mechanism is identified as induced apoptosis in the cells. Further investigation is warranted to elucidate the biochemical response and determine the derivates of ATR in this species.

Anatomy and transcriptomics of the common jingle shell (Bivalvia, Anomiidae) support a sensory function for bivalve tentacles

Animals have evolved numerous mechanisms to perceive and interact with the environment that can be translated into different sensory modalities. However, the genomic and phenotypic features that support sensory functions remain enigmatic for many invertebrates, such as bivalves, an ecologically and economically important taxonomic group. No repertoire of sensory genes has been characterized in bivalves, representing a significant knowledge gap in molluscan sensory biology. Here, we gather multiple lines of evidence to explore the specialized sensory function of bivalve tentacles in the common jingle shell, Anomia simplex. In addition to applying microscopy techniques, we performed transcriptome sequencing of dissected tentacles using phylogenetically-informed annotation to identify candidate receptors. Our results demonstrate the expression of candidate GPCRs, including one opsin type, five small-molecule receptors, and 11 chemosensory-related receptors, supporting the involvement of sensory neurons in the organ, likely in association with the ciliated receptor cells observed along the tentacle surface. In addition, we identified seven ionotropic receptors as putative chemosensory receptors and one member of the Piezo mechanosensitive ion channel, which might be involved in touch sensation by ciliated sensory receptors. Our results provide the first evidence of putative sensory genes expressed in a bivalve sensory organ, representing an important starting point to investigate chemosensation in this class.

Form and function of tentacles in pteriomorphian bivalves

Tentacles are remarkable anatomical structures in invertebrates for their diversity of form and function. In bivalves, tentacular organs are commonly associated with protective, secretory, and sensory roles. However, anatomical details are available for only a few species, rendering the diversity and evolution of bivalve tentacles still obscure. In Pteriomorphia, a clade including oysters, scallops, pearl oysters, and relatives, tentacles are abundant and diverse. We investigated tentacle anatomy in the group to understand variation, infer functions, and investigate patterns in tentacle diversity. Six species from four pteriomorphian families (Ostreidae, Pinnidae, Pteriidae, and Spondylidae) were collected and thoroughly investigated with integrative microscopy techniques, including histology, scanning electron microscopy, and confocal microscopy. Tentacles can be classified as middle fold tentacles (MFT) and inner fold tentacles (IFT) according to their position with respect to the folds of the mantle margin. While MFT morphology indicates intense secretion of mucosubstances, no evidence for secretory activity was found for IFT. However, both tentacle types have appropriate ciliary distribution and length to promote mucus transportation for cleaning and lubrication. Protective and sensory functions are discussed based on different lines of evidence, including secretion, cilia distribution, musculature, and innervation. Our results support the homology of MFT and IFT only for Pterioidea and Ostreoidea, considering their morphology, the presence of ciliated receptors at the tips, and branched innervation pattern. This is in accordance with recent phylogenetic hypotheses that support the close relationship between these superfamilies. In contrast, major structural differences indicate that MFT and IFT are probably not homologous across all pteriomorphians. By applying integrative microscopy, we were able to reveal anatomical elements that are essential for the understanding of homology and function when dealing with such superficially similar structures.