Gastropods of the family Epitoniidae (Caenogastropoda) are ectoparasites of anthozoans but the host specificity and preference remain to be investigated for numerous taxa. In this study, the host use of the intertidal epitoniid species Epitonium japonicum was investigated by field observations and laboratory feeding experiments. The field observations were conducted at Tateyama, Chiba, central Honshu Is., Japan in 1996 and 2025. Epitonium japonicum was found parasitizing two actiniid sea anemones, Anthopleura uchidai and A. cf. inornata, with the prevalences of 4.9-18% and occupancies of 1-7 individuals. The feeding behavior of E. japonicum were tested for 12 sea anemone species of five families. Other than A. uchidai and A. cf. inornata, E. japonicum fed on three species of Anthopleura, which are distributed sympatrically with the snail. The hosts of E. japonicum may restrict to the single genus, suggesting its moderately high host specificity. In addition, sand deposit around sea anemones, where the snails were found during the field observation, might provide a cryptic, stable habitat to the snails and therefore be important for their co-occurrence. The phylogenetic position of E. japonicum was also investigated based on four-gene sequences (2,490 sites). Epitonium japonicum formed a robust clade with three congeneric species parasitizing actiniids, particularly Anthopleura spp. The host use of E. japonicum may be determined by the combination of phylogenetic constraints of the snail and host, the species composition of available sea anemones, and abiotic conditions.
Marine planktonic copepods are highly diverse in the mesopelagic zone, where marine snow is among the major food sources. Although marine snow composition varies with origin, whether this influences copepod feeding ecology remains poorly understood. We investigated the gut microbiota of mesopelagic copepods, Pleuromamma xiphias, Spinocalanus magnus, and Scottocalanus securifrons via high-throughput 16S rRNA gene amplicon sequencing and compared them relative to their gut morphology and feeding habits. Among gut bacteria, Synechococcus and Planctomycetes, both aggregate-associated bacteria, were the most abundant in all samples, suggesting copepod feeding on marine snow. Photobacterium, which has chitinases and includes luminous species, was significantly more abundant in Sc. securifrons, which has a red-colored gut, than in Sp. magnus and P. xiphias, both of which have semi-transparent guts. Phylogenetic analysis of the LuxA gene revealed that Photobacterium sequences from the Sc. securifrons samples formed a distinct clade within the genus but did not correspond to known species, suggesting a possible relationship between bacterial bioluminescence and the red coloration of the gut. Gut microbiota composition differed among the three species at phylum and genus levels, with Sp. magnus showing the most specialized profiles reflecting its phytodetritus-based diet and P. xiphias exhibiting more diverse composition consistent with its generalist feeding. These results indicate that gut microbiota differences are associated with feeding habits and gut morphology, potentially reflecting types of marine snow ingested. Future studies should compare gut microbiota with bacterial communities of individual marine snow particles to clarify how specific bacterial groups relate to copepod feeding habits.
We describe here a new species of Perkinsiana (Annelida, Polychaeta, Sabellidae) from the rocky shore of Akkeshi, Hokkaido, Japan. Perkinsiana yezo sp. nov. is characterized by the presence of long ventral lappets on the collar, rectangular ventral shields, short handles of both thoracic uncini and companion chaetae, and pattern of hoods of abdominal chaetae (type B sensu Tovar-Hernandez et al. 2012). We compare the new species to congenerics in the world ocean.
beta-N-methylamino-L-alanine (BMAA) is a non-proteinogenic amino acid produced by certain cyanobacteria and diatoms, and is suspected chronic neurotoxin. Although BMAA and its structural isomers, 2,4-diaminobutyric acid (2,4-DAB) and N-(2-aminoethyl)glycine (AEG), have been found in aquatic food webs in other countries, their presence in Japanese waters and shellfish had not been reported. In this study, we quantified BMAA and its isomers in Japanese shellfish using a non-derivatized LC-MS/MS method. BMAA concentrations in shellfish ranged from below the detection limit to 16.0 & micro;g g-1 dry weight (dw), and tended to be higher in filter-feeding bivalves compared to gastropods. 2,4-DAB was present in all shellfish species (0.0818-13.0 & micro;g g-1 dw), whereas AEG was only detected in some bivalves, with high levels found in Spisula sachalinensis (Schrenck, 1861) (8.55-25.5 & micro;g g-1 dw). BMAA was also detected in particulate organic matter from Tokyo Bay (0.0186 & micro;g L-1), suggesting that suspended microalgae could be a source of exposure for benthic filter feeders. Our results provide the first baseline data of BMAA-related compounds in Japanese shellfish and highlight the need for continued monitoring to evaluate dietary exposure risks.
Predators must capture prey. They can engage in active searching and/or sit-and-wait behaviors. Neptunea arthritica uses both behaviors to prey on various animals ranging from sessile to mobile species. This paper describes the repertoire of these behaviors toward mobile gastropod prey at the individual level in the laboratory. We conducted 201 feeding trials and analyzed 451 cases of predation in 107 trials. Active searching was used at least once in 104 trials and sit-and-wait in 67 trials. Individuals often used both behaviors (64/107). Those that used only one behavior (43/107) favored active searching (40/43). Active searching was the most common behavior toward all prey species. This study is the first case in gastropod research to clearly define the two tactics and to quantitatively describe the patterns of tactic use at the individual level. The benefits of using a sit-and-wait tactic against mobile prey are discussed from the perspective of energetic efficiency.
