Two individuals of “monster larvae” belonging to the genus Cerataspis (Decapoda: Penaeoidea: Aristeidae) were collected in the western North Pacific in 2016. The smaller one (carapace length 7.3 mm) was collected by daytime plankton net operation towed at a shallow layer (25 m to the surface), and the larger one (carapace length 11.5 mm) was collected by a nighttime plankton net operation towed from 208 m to the surface. These larvae have a pair of large spines on the lateral surface of the carapace, and in this regard they agree with C. petiti Guérin-Méneville, 1844 reported from the Atlantic. However, the mitochondrial 16S rDNA sequences of these two individuals matched with those of C. monstrosus Gray, 1828, the senior synonym of the widely used name Plesiopenaeus armatus (Spence Bate, 1881), suggesting that the presence and absence of the spine might be intra-specific morphological plasticity or variations among different developmental stages.

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We investigated genetic population structure and tetrodotoxin (TTX) content of yellowfin toxic goby Yongeichthys criniger in the Japanese coastal area. Two divergent mitochondrial lineages (lineages A and B) were found, and the frequencies were clearly different among Okinawa-Iriomote Island, Amami Oshima Island and northward of Yakushima Island. Genetic heterogeneity among three groups were supported by principal coordinate analysis based on the pairwise FST values. TTX contents were measured in goby samples from Kochi Prefecture (Kashiratsudoi River) and Yakushima Island (Isso Port and Anbo River). TTX contents of skin and muscle tissues of Kashiratsudoi River and Isso Port samples were relatively high, while TTX was not detected in most individuals collected in the Anbo River. Therefore, it is suggested that the TTX contents of this species considerably vary even among geographically close areas and/or seasonally.

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Genetically distinct three types (designated as A, B and C) in the common freshwater shrimp Palaemon paucidens in Japan have been determined using allozyme, 18S rDNA and 16S rDNA analyses. Based on the morphological and genetic analyses, Katogi et al. (2019) proposed type B population distributing in the northern Japan to be a new species Palaemon septemtrionalis. In the present study, phylogenetic analysis in amphidromous type B was performed using 16S rDNA sequences of 185 individuals collected throughout the distributional range of this species in Japan. Two highly divergent clades (designated as B-I and B-II) were observed in the phylogenetic tree, in which the mean nucleotide sequence divergence (K2P) between the clades was 3.9 %. B-II clade was further subdivided into subclades B-IIa and B-IIb, in which the mean K2P between the subclades was 1 %. Geographic distributions of these clades were clearly separated. B-I corresponding to P. septemtrionalis was distributed in the northern Japan (north of Miyagi Prefecture to Hokkaido) and rivers on the Sea of Japan side. B-IIa and B-IIb were observed in rivers on the Pacific Ocean side. B-IIa was distributed from the northern Japan (north of Miyagi Prefecture) to central Japan (Kanagawa Prefecture) and B-IIb from central Japan (Shizuoka Prefecture) to southern Japan (Kyushu). Northern area of Miyagi Prefecture was determined to be the boundary zone between B-I and B-IIa, where B-I and B-IIa individuals were observed to coexist in a river of the Oshika Peninsula. Sagami Bay at central Japan was considered to be the boundary between B-IIa and B-IIb. In the appendage morphology, longer propodus than carpus in the second pereiopod, that was reported as one of specific characteristics of P. septemtrionalis, but we found this to be size dependent characteristic and not to be applicable for species identification.

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We compared the feeding patterns of marbled flounder Pseudopleuronectes yokohamae in Tokyo Bay between 1980s (high abundance) and 2000s (low abundance). The stomach contents weight was significantly lower in 2000s compared to that in 1980s. The dietary composition changed substantially between 1980s and 2000s; main constituents of the stomach contents were annelids, molluscs and echinoderms during 1980s. In 2000s, however, they fed predominantly on annelids. Observed changes in the stomach contents may be associated with changes in abundance and species composition of macrobenthic community, and could have affected changes in the growth and reproductive patterns between 1980s and 2000s.

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クモガニ上科の中で原始的な位置づけのクモガニ科のなかで、ヒラアシクモガニ属（Platymaia）は10種が知られ、この内4種がわが国に分布しているが、いずれも深海種であるため初期発育史に関する知見に乏しい。これまでに本属ではヒラアシクモガニ（Platymaia alcocki）の第1ゾエアが、また韓国産のヒラアシクモガニモドキ（P. wyvillethomsoni）の第2ゾエアまでが記載されている。今回、ヒラアシクモガニの抱卵雌からふ化ゾエアを得て、これまでに知られている本属の幼生形態と比較した。これらの種において主要な幼生形質ではほぼ一致したが、頭胸甲長や第1小顎の剛毛配列などで異なる部分もみられた。特に重要形質の１つである第1小顎内肢の毛式は寺田（1985）では「1,5」であるが、今回の結果では「1,6」で、ヒラアシクモガニモドキと同じであった。また、本属の小顎・顎脚の内肢毛式、第2触角や尾節の形状は、これまでに知られる中ではオーストンガニ属（Cyrtomaia）に近いが、その他の属とは異なっている。クモガニ科内においては属によるゾエア形質の変異が大きく、今後より多くの種での記載が望まれる。

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小笠原諸島の南海域で採集された7および8期フィロソーマ幼生のCOI遺伝子配列を分析したところ、アカイセエビ（Panulirus brunneiflagellum）と判定され、その形態観察を行った。系統解析で示された本種の最近縁種はハワイイセエビ（P. marginatus）であり、カノコイセエビ群（‘Panulirus longipes’group）に属することが示された。また頭甲幅/胸部幅の比においても、アカイセエビはイセエビ（P. japonicus）より値が大きく、よりカノコイセエビ群に近いことが示された。

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チゴダラとエゾイソアイナメ間には顕著な形態差がなく同種の可能性が指摘されてきたものの本邦ではこれらを別種として扱ってきた。その根拠として、前者は東京湾以南の深海（150‒650m）に分布し、眼径が大きく体色が淡褐色であること、後者は函館以南の浅海（数10m以浅）に分布し、眼径が小さく体色が濃褐色であること、が挙げられている。本研究では北海道から神奈川県の範囲で44個体のチゴダラ類標本を採集し、上記の表現型とともにミトコンドリアDNAの3領域（COI、16S rDNA、Dloop）の塩基配列を分析した。体色は個体間変異が大きいものの浅場標本（80m以浅）では濃褐色個体が多く、深場標本（200m以深）では淡褐色個体が多かった。眼径/吻長も個体間変異が大きく深場標本と浅場標本の平均値間に有意差はなかった。個体間および浅深標本間の遺伝的差異は非常に小さく種内個体間レベルの範囲であることが示された。データベースより入手したチゴダラ属他種の配列を加えた系統樹解析においても、本研究で分析した個体は全て独立したクレードに属し同種と考えられた。以上のことからチゴダラとエゾイソアイナメは同種であり、体色や眼径の変異は種内個体間差であることが示された。

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Abundance of the invasive and predatory moonsnail Laguncula pulchella was investigated at 10 tidal flats along the coast of Hiroshima, western Japan. They were found from two tidal flats where this species has already been known to occur. The size and density of egg collars of L. pulchella became smaller from 2015 to 2017 but thereafter recovered in 2018. This tendency was common between the two sites, indicating that the population and body size of adult L. pulchella are highly variable among years.

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スジエビ（Palaemon paucidens De Haan, 1844）には遺伝的に異なる3タイプ（A、B、C）が発見されていることから複合種であると考えられる。2世紀近く前にシーボルトが採取しオランダの国立民族学博物館に収蔵されているタイプ標本の16S rDNAを分析したところ、AタイプのうちJA1ハプロタイプであることがわかった。JA1タイプは日本中部から南部にかけて最も多く出現するタイプであり、長崎周辺に限られていたシーボルトの活動範囲とも符合する。

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Four specimens of the freshwater palaemonid prawn, three Macrobrachium australe and one M. lar, were collected in the Koonoura River, Nagasaki, Japan. The former is the first record in Nagasaki Prefecture. Occurrence of these species was thought to be due to larval dispersal by branched flow from the Kuroshio Current. However, these two species are unlikely to overwinter, because the samples are only subadults and the water temperature of this river drops below 10 °C in winter.

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