The purpose of present study is to clarify the predation of P. japonica including larvae by investigating guts of predators caught as a by-catch in the P. japonica fishery. The by-catch, including fish, cephalopods and decapods, were caught once or twice a month between April and November 2008 in a submarine canyon adjacent to the mouth of the Jinzu River in Toyama Bay. Size of the potential predators was measured and the gut contents were identified to the lowest possible taxa. Ostracods, copepods, mysids, cumaceans, amphipods, euphausiids, and decapods were the most common prey in the gut contents of the predators. Pasiphaea japonica, including larvae before metamorphosis, were preyed upon by demersal fishes Crystallichthys matsushimae, Lycodes nakamurae, and Bothrocara hollandi. Occurrence of P. japonica in the guts of these predators may be due to the aggregation of larvae in the canyon head which is enclosed by the steeply sloping bottoms and the truncation of the vertical migration of P. japonica from the pelagic to the benthopelagic environment.

Elthusa moritakii sp. nov., a branchial parasite of the deepwater bullhead sculpin Ereunias grallator, is described from Japan. The new species is morphologically similar to Elthusa propinqua (Richardson, 1904), but can be distinguished from the congener by a combination of characteristics of ovigerous females, including pereopods 5–7 with unexpanded carina, number of robust setae on maxilla, greatest width of pleon, shape of pleopods, and length of pleotelson. Further, new host records of E. propinqua are here reported. This species was recently collected from five macrourid fish species from Japan, including the grenadiers, Coelorinchus jordani, C. longissimus, the spearnose grenadier, C. multispinulosus, the unicorn grenadier, C. productus, and the Sagami grenadier, Ventrifossa garmani.

Autotomy is a common phenomenon in crustaceans and has been extensively studied. The Japanese mitten crab, Eriocheir japonica, is an important fisheries species in Japan, but autotomy patterns of this species have seldom been reported. Therefore, in this study, we examined the autotomy patterns for E. japonica in both growth and reproduction habitats. Our results indicated that a high proportion (more than 26%) of E. japonica lost appendages, and autotomy rate was positively correlated with crab size. There was no significant difference in autotomy frequency between sexes, and single appendage loss was the most common form of autotomy. Appendages on the left and right sides had an equal probability of loss. The observed autotomy frequency was significantly different from the expected frequency, which suggests that in E. japonica the autotomy event is dependent on each other. Moreover, appendage loss in E. japonica was affected by habitat type and season.

Echinoids comprise an integral component of coral reef ecosystems, providing trophic links, microhabitats, and refuge for a wide diversity of symbiotic organisms. We studied the association of at least eight species of decapod crustacean ectosymbionts with six species of echinoids at Roatán, Honduras, during 6–11 September 2015. Decapods associated most frequently with the echinoid Diadema antillarum (10.80% of individuals of this echinoid, six decapod species; n=799), followed by Eucidaris tribuloides (1.74%, three species; n=746), Echinometra lucunter (1.30%, six species; n=8349), Tripneustes ventricosus (0.86%, four species; n=1167), Echinometra viridis (0.23%, two species; n=862), and Lytechinus variegatus (0%, no species; n=12). Of 239 individual decapods observed, Percnon gibbesi was the most common species (48.5% of decapods, four echinoid species), followed by unidentified hermit crabs (Paguridae; 27.2%, five species), Stenorhynchus seticornis (11.7%, three species), Stenopus hispidus (6.3%, three species), Plagusia depressa (3.3%, three species), Panulirus argus (1.3%, one species), an unidentified small crab (possibly Pitho sp.; 1.3%, one species), and Mithrax verrucosus (0.4%, one species). The frequency of association varied with water depth for P. gibbesi, which associated more frequently with D. antillarum in shallow water (<5 m), and S. seticornis, which associated more frequently with D. antillarum in deep water (>5 m). None of the decapod species associated exclusively with echinoids or was specialized for associating with echinoids. Decapods associated with the longest-spined species, D. antillarum, at a rate more than six times higher than that of any other echinoid species, supporting the hypothesis that decapods seek shelter among the spines of echinoids to benefit from decreased predation.