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In 2001, many planktonic larvae of the lancelet Branchiostoma japonicum were found in the western Seto Inland Sea. To know their subsequent state, the benthic population at a small sandbank, named Ohzu, located there was surveyed with a grab sampler in total 26 times from November 2001 to November 2005. The mean population abundance at six stations was around 100 ind. m-2 until July 2002, and abruptly increased to 1041 ind. m-2 until November 2002 by a mass recruitment. Thereafter, the abundance decreased with fluctuations to around 200 ind. m-2 in November 2005. The 2002-year class continued to be the strongest year class until at least 2005. Planktonic larvae collected in July 2005 at 4-km intervals along an 80-km line showed strongly patchy aggregations with scales ranging 4 to 12 km. Their patchy aggregation probably resulted from a spawning habit known for lancelets, which spawn within a short time at night and synchronously a few times in summer. The mass recruitment in 2002 and the large interannual fluctuation of the benthic population were most likely caused by the accidental settlement of patchy larval aggregation. Populations at Ohzu and a site (Kaihara) about 6.5 km apart in June 2006 showed a similar age structure having the strongest age class is still regarded as the 2002-year class, suggesting that the two sites were settled by the same larval patch or different patches with different fertilization dates. [ABSTRACT FROM AUTHOR]

Ariake Bay has Japan's biggest nori seaweed farming field in the innermost part and has suffered from environmental degradation since the late 1990s. To elucidate the seasonal patterns in the copepod community structure in the inner bay, we examined monthly plankton-net samples collected in the top 2-m layer at 11 stations for 5 years from April 2002 to March 2007. Of the 11 stations, 7 were at the high-turbidity site (HTS) representing the nori farming field and 4 in the offshore low-turbidity site (LTS) for comparison. The copepod community in the HTS was dominated almost year round by Oithona davisae, whose 5-year mean abundance of 203 ind. L-1 comprised 84% of copepods and was more than double that in the LTS. O. davisae became extremely abundant in summer with the maximum monthly mean abundance in the HTS of 2756 ind. L-1 and the maximum sample-specific abundance of 10116 ind. L-1. The following predominant copepods in the HTS were Parvocalanus crassirostris in summer-autumn, Microsetella norvegica in summer, Acartia omorii in spring, and Paracalanus parvus s.l. irregularly. Possible causes for high abundance of O. davisae in the HTS are assumed to be sufficient food resources, water temperature over 21°C, and a wide salinity tolerance range of the species. [ABSTRACT FROM AUTHOR]

The Paracalanus parvus (Claus, 1863) species complex is a common marine calanoid copepod found in the world's oceans. Recent genetic analyses of its specimens from the world oceans revealed that the complex in the western North Pacific consists of three species, i.e., P. indicus Wolfenden, 1905, P. tropicus Andronov, 1977 and an undescribed species. We assign the last one to be Paracalanus orientalis n. sp. by comparing it with previous morphological descriptions of related species. Both sexes of the new species are fully described based on genetically identi- fied specimens from the surface layer of the south of Japan. The new species can be reliably distinguished from P. indicus and P. tropicus by the hunchback shape of the female if it is clearly present. Among the three species, the high length:width ratio of the third exopod segment of leg 4 is also characteristic of the new species, which would be identi- fiable, in most cases, by having a ratio of 5.4 or more. [ABSTRACT FROM AUTHOR]

Neutrodiaptomus formosus (Kikuchi, 1928) is a calanoid copepod found in freshwater ponds in Japan. In the original description of this species, the illustration of the female habitus and the diagnostic description of the genital double somite were based on the copepodid V stage. Since there have been no studies describing the adult female of N. formosus, we redescribed fully both sexes of adults. The female genital double somite has a prominent projection at the right posterior corner, which is unique in this genus. Some differences between N. formosus and a previous description of the congener N. tumidus were found in the segmentation and setation of the cephalothoracic appendages. A key to females of 11 diaptomid species occurring in Japanese freshwaters is provided, because the previous keys so far were based mainly on male characters. [ABSTRACT FROM AUTHOR]

The brackish-water calanoid copepod known as Pseudodiaptomus inopinus in the mainland of Japan consists of two genetically separate species. One is P. japonicus, which was once synonymized with P. inopinus but was recently revived. This paper describes the other species as Pseudodiaptomus yamato n. sp., which is confirmed to have morphological differences from P. inopinus s.s. based on specimens from the type locality (Lake Taihu, China) of the latter. We also redescribe P. japonicus and P. inopinus s.s. for comparative purposes. The three species are distinguishable by the combination of the following morphologies: 1) weak or prominent posterior round projections of the female last pediger; 2) relative length of posterior processes of the female genital operculum; 3) presence or absence of medial spinules on the first exopodal segment of the female leg 5; and 4) the size of spinules at the center of the ventral surface of the male second urosomite. Significant inter-population variation is observed in some spinules of P. japonicus. The past and present records indicate that Pseudodiaptomus yamato n. sp. is endemic to Japan and confined to the coasts affected by the warm Kuroshio Current from western Kyushu to the middle of Honshu, while P. japonicus is widespread in northern East Asia without overlapping the range of P. yamato n. sp. The range of Pseudodiaptomus inopinus s.s. most certainly does not extend to those of P. yamato n. sp. and P. japonicus. [ABSTRACT FROM AUTHOR]

Pseudodiaptomus inopinus, a common estuarine calanoid copepod in the Northwest Pacific, has been suggested to be a species complex. The population of the mainland of Japan consists of two allopatric forms that are distinguishable by the length of the posterior processes of the genital operculum; the forms with short and long processes are tentatively called SP- and LP-forms, respectively. We analyzed the mitochondrial cytochrome c oxidase subunit I (COI) gene and the nuclear ribosomal internal transcribed spacer 1 (ITS1) gene of 34 individuals (12 SP- and 22 LP-forms) collected from various localities. The genetic differences between the two forms were 12-15% for COI and 7-10% for ITS1. They were clearly separated into different clades in both COI and ITS1 trees. These results confirmed that the two forms belong to different species. The SP-form is a distinct species because the shape of the genital operculum of P. inopinus s. str. has long posterior processes as in the LP-form. Pseudodiaptomus japonicus Kikuchi, 1928, which is the SP-form and was once synonymized with P. inopinus, is revived. The genetic comparison using available sequence data indicates that Pseudodiaptomus koreanus Soh et al., 2012 is the same species as P. japonicus. [ABSTRACT FROM AUTHOR]

High-concentration pure glycerol has been used as a medium for permanent preservation of micro-crustacean specimens. However, glycerol-mounted permanent slide preparations are rare because of the difficulty in sealing the coverslip over the long term. I devised a glycerol-mounted permanent preparation method, especially for a small dissected piece of a micro-crustacean using a glass depression slide and a coverslip with secure sealing, in order to overcome some of the disadvantages of the popular permanent mountants that solidify, such as discoloration of specimens and difficulty in remounting. Unique characteristics of the preparation method are: (1) the central glycerol being of a few millimeters in diameter, which embeds the specimen and is retained in the depression center by a paraffin wax circle painted on the depression bottom; (2) the marginal glycerol, which fills up the clearance between the glass slide and the coverslip and prevents intrusion of the sealant into the clearance; (3) sealing with nail polish first and Canada balsam second, where the latter can seal securely over the long term and the former, being a fast-drying sealant, prevents intrusion of the latter into the marginal glycerol. By following this method, even a small dissected piece can be easily found under a microscope and taken out from the preparation for detailed examination with a low risk of going missing. The procedure to make the preparation is presented in detail. [ABSTRACT FROM AUTHOR]

The estuarine planktonic calanoid copepod Eurytemora americana is described for the first time from Japan based on specimens from Dokai Bay, a small inlet of northern Kyushu in 1975, when the species was exclusively dominant in the innermost bay. This is the southernmost record of the species in the Northern Hemisphere. Morphological descriptions are provided, especially on characters different from or overlooked in previous descriptions. Compared with the recent description of the species from Korea, a distinct morphology is found in the spinule number on the male fifth leg, suggesting inter-population variation and therefore no gene flow between the Japanese and Korean populations. Eurytemora americana in Dokai Bay is regarded as an invasive alien species introduced via ship ballast water. Despite the dominance in 1975, the copepod was not collected from brackish waters in the innermost part of the bay in 2008. Global warming in spring and/or winter periods after the 1970s is a possible reason for the disappearance of this cold water species. [ABSTRACT FROM AUTHOR]

The life cycle and precopulatory mate guarding behavior of the poecilostomatoid copepod Goidelia japonica associated with the spoon worm Urechis unicinctus (Echiura) are described based on specimens from 19 worms collected from western Japan. A total of 676 copepods were collected from the host's rectum (494 copepods) and body surface (182 copepods). Copepod numbers were significantly correlated with host weight. Copepods in the rectum consisted almost completely of copepodids (35%) and adult males (65%), with only one non-ovigerous adult female recorded. In contrast, those on the body surface were all adult males (24%) or females (76%), of which 58% were ovigerous. No nauplii or CI occurred. In the rectum, 36% of the adult males guarded 67% of the copepodids, consisting of CII-CV. From these results, their life cycle is considered as follows: nauplii and CI live as plankton; just before or after molting to CII, they enter the host's rectum and females are probably soon guarded by males; they grow up to CV there; CV females guarded by males move to the body surface just before the final molt; on the body surface females molt to adults and spawn eggs. Guarding the first symbiotic stage (CII) is a unique precopulatory behavior for symbiotic poecilostomatoid copepods. This can be explained from the viewpoint of evolutionary resolution of the intersexual conflict and advantage for early copepodids in precopula. [ABSTRACT FROM AUTHOR]

Copepod nauplii are the primary food item for early-stage marine fish larvae, but their feeding selectivity on the nauplii of different copepod species has not been well studied. This study revealed feeding selectivity in the dominant preflexion larvae of three fishes Sebastiscus marmoratus, Sebastes sp. and Ammodytes japonicus in the Seto Inland Sea, Japan, in spring and winter. Copepod nauplii and eggs numerically constituted 80-91% of the prey items in their guts. Chesson's preference index for the nauplii of various copepod species was positive for Calanus sinicus and Paracalanus parvus sensu lato, negative for Acartia omorii, and negative or neutral for Oithona similis. This result is probably attributable to the size and swimming behavior of the prey species. The preference index in A. japonicus larvae was not significantly different between the nauplii of different species, suggesting that the larvae are less selective than the other two fishes. The preference index for Calanus eggs was very high, especially in Sebastiscus marmoratus and Sebastes sp., and most of the eggs in the guts were shrunken, probably due to digestion. In terms of volume, C. sinicus nauplii and eggs in gut contents represented 36-72% of total copepod nauplii and >80% of total copepod eggs, respectively, because of high selectivity by fish larvae and their large individual volumes compared with the dominant copepods. This indicates that C. sinicus is the most important prey species for early fish larvae despite their low abundance in the environment. [ABSTRACT FROM AUTHOR]

Two new poecilostomatoid copepod species, Kelleria japonica n. sp. and K. pararegalis n. sp., belonging to the family Kelleriidae are described from an eelgrass bed on the southwest coast of Shikoku Island, western Japan. The family is new to the fauna of Japan. Kelleria japonica is similar to four congeners by having a bilobed medial process on the female leg 5, but distinguished from them by a combination of features in some of the following appendages, the caudal ramus and the terminal spines of the maxilla in both female and male, the female leg 5, and the male legs 1 and 2. Kelleria pararegalis is most similar to K. regalis, described from the Suez Canal, but differs from the latter in the body length in both female and male, the medial process on the first segment of the maxilliped and the inner apical spine of leg 5 in the female, and the outer apical spine of the leg 2 endopod in the male. [ABSTRACT FROM AUTHOR]

Nine specimens of the planktonic chaetognath Eukrohnia kitoui, which was originally described from Tokyo Bay 32 years ago, were collected from an underwater canyon in Tosa Bay, Japan. This is the second record of the species. We compared E. kitoui and the closely allied E. calliops based on individual data of the two species reported in the previous and the present studies. Since allometric growth was observed in morphometric characters, specimens smaller than 10 mm in body length were omitted in this comparison. The results revealed that the ratios of tail segment and eye lengths to body length and the numbers of hooks and posterior teeth on the head, which were described as distinguishable features between the species in the previous study, were significantly different between the species. However, the values of these characters overlapped between the species except for the eye/body ratio, indicating that the eye size is the most critical feature distinguishing them. The present specimens showed that the relative position of the transverse musculature to the ventral ganglion, which was another diagnostic character of E. kitoui in the previous study, varied greatly according to growth. Considering the characteristic sampling sites (underwater canyons) and a long absence of occurrence records, E. kitoui is probably a rare species restricted to waters in or near coastal underwater canyons, as observed in E. calliops. [ABSTRACT FROM AUTHOR]