The distribution of protistan microplankton situated southwest (S09) and northeast (S18) of the Izu Ridge along the Kuroshio Current was revealed by 18S rRNA gene clone analysis. A total of 257 clones were identified, consisting of 65 phylotypes of dinoflagellates, 49 phylotypes of diatoms and 57 phylotypes of other protists affiliated with Ciliophora, Cryptophyta, Cryptophyta nucleomorph, Choanoflagellata, Chlorophyta, Cercozoa, and Heterokonta. The dinoflagellate phylotypes were affiliated with five genera and 14 uncultured groups, with Gyrodinium as the most frequently detected genus. The diatoms were also well represented and consisted of 13 genera and six uncultured groups. The clones belonging to the genus Pseudo-nitzschia were most frequently detected. The frequencies of dinoflagellate clones and phylotypes were higher at station S09 in the south than at station S18 to the north, with the frequency of diatom phylotypes being higher at the latter. The species richness (number of phylotypes) and diversity (Shannon-Wiener) of the protistan microplankton community were slightly higher at S18 compared to S09. When the Kuroshio Current encountered with the Oyashio Current at northwestern Pacific, it affects the water temperature and nutrients of the Kuroshio Current. The clone analysis results showed a difference in the protistan microplankton community at both stations due to the collision of both currents.

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Medusae of an undetermined species of the carukiid genus Malo were sampled for life cycle research at Port Douglas Marina, Port Douglas, Australia, in 2011. Due to confusing character variations within the specimens, identification to species level initially seemed impossible. To resolve their identity, the type material of Malo maxima Gershwin, 2005 and M. kingi Gershwin, 2007 were examined. Comparisons were made of the two, and also with the unknown species. Unexpectedly, no significant differences were found between M. maxima and M. kingi. Moreover, all character variations in them were observed as well in the unknown species. Accordingly, M. maxima from Western Australia and M. kingi from Queensland are considered to represent populations of the same species. Characters considered both reliable and unreliable for species determination in the genus are discussed, and an emended diagnosis of Malo is proposed. The earlier name M. maxima is proposed for both populations and for the specimens from Port Douglas.

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The Sea of Japan is a semi-closed marginal sea where genetic break and/or speciation have been reported for some deep-sea taxa. Population structure was compared between the congeneric deep-sea flounder species Hippoglossoides dubius and H. pinetorum inhabiting the Sea of Japan and neighboring seas. Based on nucleotide sequences of mitochondrial control regions, the H. dubius population was concluded to be genetically homogeneous, while 2 genetically distinct groups were recognized among H. pinetorum. Although the rare group of H. pinetorum populates the Sea of Japan, the Yellow Sea, the Okhotsk Sea, and the northwestern Pacific, frequency was the highest in the Sea of Japan. The unique phylogeographic pattern of H. pinetorum may be attributable to secondary contact with the Sea of Japan lineage, which was isolated from other sea areas during the last glacial period. A difference in bathymetrical distribution between the two species might explain their contrasting genetic population structures.

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The size of medusa populations in most scyphozoan species can be affected by the size of their benthic polyp populations, which reproduce asexually to give birth to planktonic ephyrae, but also are subject to predation by natural enemies. In this study, five gastropod species (Calliostoma unicum, Pleurobranchaea japonica, Hermissenda crassicornis, Sakuraeolis enosimensis and S. sakuracea) and three crustacean species (Rhynchocinetes uritai, Latreutes anoplonyx and Hyastenus diacanthus) were found to prey on polyps of the moon jellyfish, Aurelia aurita s.l., in Japanese coastal waters. In particular, C. unicum, P. japonica, H. crassicornis, R. uritai and H. diacanthus consumed more than 300 polyps per predator per day in the laboratory. These predators are common on natural rocky or pebbled seabeds, but are very scarce on various substrates in concrete-walled fishing ports, particularly on the undersurfaces of floating piers, where A. aurita polyps are attached in abundance. Transplanting natural predators to substrates with dense polyp colonies, just prior to their seasonal strobilation, is a possible countermeasure to prevent recurrent medusa blooms.

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The saltmarsh sesarmid crab, Clistocoeloma sinense, inhabits the muddy substrata in upper intertidal saltmarshes, and is designated as endangered in Japan. Seasonal changes were investigated in population characters, including abundance, time to sexual maturity, reproductive season, and recruitment of juveniles in a regional metapopulation in Tokyo Bay. Crab samples were collected monthly at five small isolated habitats along the coast of the bay from July, 2011, to March, 2013. Ovigerous females were found during summer in a single peak, and a peak of juvenile recruitment occurred in autumn. Size distribution analysis indicates that growth is slower than for other saltmarsh crab species and life span is at least 4 years. Females reach maturity when they enter the second breeding season following recruitment. The slow growth and reclusive behavior of C. sinense may be closely related to the characteristics of its habitat which is under buried stones or wood in the uppermost part of intertidal muddy substrata. Recruitment of juveniles and the presence of breeding females were observed at all five study sites located along the Tokyo Bay coastline, suggesting that each population stably regenerates by larval settlement following larval dispersal and growth in the water column in Tokyo Bay. These data suggest that an increase in the number of small muddy flats with intertidal salt marsh vegetation along the coastline may be the most effective measure to conserve the Tokyo Bay regional metapopulation of this crab species.

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Most crustaceans are known to regenerate their appendages after losing them, and the pattern of regeneration may be related to its function. The pattern of regeneration of the right major cheliped was examined after experimentally induced autotomy and its behavioral function during male-male contests for mates was investigated in the hermit crab Pagurus middendorffii. Males with an autotomized major cheliped regenerated it at the first molt after autotomy and showed smaller growth in body size than in control males. The shape of the regenerated cheliped was more slender than the original, implying that the regenerated major cheliped would be less robust and weaker than previously. The length of the major cheliped of an owner male (guarding a female at the start of a dyadic contest) and the body size of an intruder affected whether or not the contest escalated, but the major cheliped length of the intruder and the body size of the owner determined the outcome of the escalated contest. The intruder used the major cheliped as an offensive weapon to take the female away from the owner by force after the contest escalated. The owner often moved the major cheliped forward, similar to a fencing weapon, before escalation. Such movement of the owner seems to be effective to prevent the intruders from approaching, and the regenerated cheliped of the owner may not require much robustness and strength as a defensive weapon before escalation. Rapid regeneration of the major cheliped in P. middendorffii would therefore be beneficial to minimize the disadvantages incurred by loss of the major cheliped.

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A new genus, Praestephanos, is described with its type species based on Stephanodiscus suzukii. In addition, two new combinations are described: P. triporus and P. carconensis. This genus is similar to the genus Stephanodiscus, however, the pattern of the areolae changes at the level of the marginal fultoportulae but not at the level of the rimportulae or spines, and this differs from Stephanodiscus. Five clades, Stephanodiscus, Cyclostephanos, Cyclotella ocellata–Handmannia complex, Praestephanos and Discostella were detected by molecular analysis. The Discostella clade has the most basal position of these five clades. The Praestephanos clade holds a clearly basal position in relation to the Stephanodiscus and Cyclostephanos clades. However, the relationship between Praestephanos and Cyclotella ocellata–Handmannia was uncertain. Since these four clades separated with short branches in the phylogenetic tree, these four clades (excluding Discostella) may have evolved during a very short geological period.

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Orthoprotella spinigera Mori, 1996 (Crustacea: Amphipoda: Caprellidae) was collected from a coral reef at Oura Bay on the east coast of Okinawa Island, Japan. This is only the second record for O. spinigera. The type locality is the Amakusa Islands, Kyushu, ca. 700 km north of the current collection. The species may be widely distributed along the western and southern coasts of Japan. Orthoprotella spinigera appears similar to Metaprotella sandalensis Mayer, 1898, but differs in the head having a pair of apical rounded projections, lacking a triangular projection below the eye, and having longer fused pereonites 6 and 7.

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