Taxonomic reassessment of chaetognaths (Chaetognatha, Sagittoidea, Aphragmophora) from Korean waters.

Since the first record of chaetognaths (arrow worms) reported from Korean waters by Molchanov in 1907, three families, 12 genera and 21 species have been additionally described. Eighteen of the 21 recorded species have been reported under scientific names different from the latest taxonomic system. This study aimed to address this issue by conducting a taxonomic re-evaluation of chaetognaths collected from Korean waters. Furthermore, the taxonomic usefulness of morphological differences in corona ciliata and distribution of ciliary sense receptors were re-examined using specimens stained with 1% Chlorazol black E (CBE) solution. This study includes taxonomically-validated voucher specimens of 18 species from Korean waters. Based on the specimens, re-description including image data and CBE staining pattern, distribution, ecological information and improved key were provided for each species. However, Decipisagittadecipiens, Serratosagittaserratodentata and Sagittapseudoserratodentata from Korean waters is still questioned because of the paucity of the voucher specimen and scientific literature.

Short-term variation in abundance of four Acartia species (Copepoda, Calanoida) in a eutrophic bay.

The short-term variation in the abundance of Acartia copepods in the eutrophic Gamak Bay of South Korea was investigated with weekly measurements from October 2007 to September 2008. During this period, four Acartia species (A. erythraea, A. ohtsukai, A. omorii, and A. sinjiensis) were recorded as showing seasonally different peak abundance. The abundance of A. erythraea and A. sinjiensis was high in autumn, whereas that of A. omorii was high from winter to spring. In summer, A. erythraea, A. ohtsukai, and A. sinjiensis coexisted at peak abundance significantly related to water temperature and salinity. Results from the response curves of the four Acartia species to water temperature and salinity suggest that A. erythraea and A. sinjiensis increased in abundance at water temperatures >18 °C, whereas A. ohtsukai increased in abundance at water temperatures >27 °C. The occurrence of A. erythraea, A. ohtsukai, and A. sinjiensis decreased with increasing salinity, but chlorophyll-a concentration showed no effect on occurrence. Despite these findings, the coexistence of the three ecologically similar species may be due to prey abundance in summer and autumn (chlorophyll-a concentration >10 µg L-1). Notably, the wide range of the response curve of A. omorii indicates its occurrence at higher salinity levels than other species.

Three new species of the genus Stephos Scott, 1892 (Crustacea, Copepoda, Calanoida, Stephidae) from Jeju Island, Korea.

During general field surveys carried out recently to collect benthopelagic copepods from near the substrate of the shallow waters off Jeju Island, Korea, a few specimens of three new species of Stephos Scott, 1892, were collected. The new species are placed in the genus Stephos because of the following combination of features: absence of seta on the basal exite of maxillule, and male right leg 5 ending in an unarmed claw-like and/or mitten-like segment. Stephos jejuensis sp. nov. can be distinguished from its congeners by body length 0.92 mm, left side of the female genital double-somite with protruding lobes, antennule that extends beyond the distal area of the genital double-somite, and the male leg 5 terminal complex. Stephos concavus sp. nov. can be distinguished from its congeners by the genital double-somite with protruding lobes on both sides, and the presence of larger spinules on the distomedial margin of leg 5. Stephos fortipes sp. nov. can be distinguished from its congeners by its longer body length, 1.12 mm long in the female, antennules that extend to the end of the genital double-somite, and the presence of a covered row of minute spinules on the ventral surface of the genital operculum in the female. Until now, 35 species of stephids were known worldwide.

A new species in the genus Acartia Dana, 1846 (Crustacea, Copepoda, Calanoida, Acartiidae) from the South Pacific coastal waters of Nadi Bay, Fiji.

A new species in the genus Acartia, Acartia nadiensis sp. nov., is described from Fijian coastal waters. This species belongs to the subgenus Odontacartia based on the following morphological features: presence of a rostral filaments, a pointed process on the last prosomite, a serrated terminal spine on female P5, and the absence of a protrusion on the basis of the male right P5. This new species can be differentiated from its congeners by the combination of the absence of a spine on the first segment of the antennules, the short outer seta of female P5, and a medial spine on the exp-2 of the left male P5. Phylogenetic analyses using mitochondrial COI partial sequences show that the new species is distinct from its congeners.

Prorocentrum shikokuense Hada and P. donghaiense Lu are junior synonyms of P. obtusidens Schiller, but not of P. dentatum Stein (Prorocentrales, Dinophyceae).

In Japanese, Chinese and Korean coastal waters, recurrent blooms of a small, elongate Prorocentrum species have been observed in recent years. In previous studies, this species has been respectively identified as P. shikokuense, P. donghaiense and P. dentatum, despite morphological similarity and identical rDNA sequences. To resolve the confusion, morphological features, including the architectural details of the periflagellar area, were examined and ribosomal DNA (rDNA) sequences were obtained from specimens collected from the East China Sea and Korean coast, and a strain established in the waters off the Canary Islands of Spain. In addition, the descriptions of the three species and allied species were reviewed. Morphological observations and a phylogeny based on the SSU, ITS region and LSU rDNA sequences revealed that the previously confused species and our studied strains are conspecific and that the morphology of strains identified as P. dentatum in the phylogenetic trees does not coincide with P. dentatum sensu stricto. The confusion can be traced back to Dodge (1975, p. 116), who considered P. veloi, P. monacense and P. obtusidens as junior heterotypic synonyms of P. dentatum. However, Dodge's P. dentatum are closer to P. obtusidens sensu stricto, rather than P. dentatum sensu stricto. P. obtusidens sensu stricto can be distinguished from P. dentatum sensu stricto by its relatively small size, parallel sides towards the anterior and a blunt anterior extension on one side. This indicates that P. obtusidens should not be considered a synonym of P. dentatum sensu stricto. In addition, a comparison of the original descriptions of P. obtusidens and allied species allowed to conclude that small, elongate Prorocentrum from Japanese, Chinese and Korean coastal waters previously identified as P. shikokuense, P. donghaiense, P. dentatum sensu Yoo and Lee (1986) and the specimens studied herein, which share identical rDNA sequences, morphologically coincide with P. obtusidens. Therefore, it is proposed that P. shikokuense and P. donghaiense should be regarded as junior synonyms of P. obtusidens.

Three new species of Heteromastus (Annelida, Capitellidae) from Korean waters, with genetic evidence based on two gene markers.

Three undescribed species of Heteromastus Eisig, 1887 were collected from intertidal to sublittoral habitats in western and southern waters of Korea. Heteromastus namhaensis sp. nov. is distinguishable from other congeners by the presence of hemispheric notopodial lobes in the posterior abdomen. Heteromastus gusipoensis sp. nov. closely resembles H. tohbaiensis Yabe & Mawatari, 1998 in the absence of posteriorly extended abdominal notopodial lobes, but differs in the absence of eyespots on the prostomium and distinct node on the shaft of thoracic hooks in H. gusipoensis. Heteromastus koreanus sp. nov. is similar to H. filiformis sensu Hutchings & Rainer, 1982 in the shape of abdominal notopodia, but clearly differs in dentition of the abdominal hooks and methylene green staining pattern (MGSP). DNA sequences (mtCOI and histone H3) of these new Korean species were compared with all sequences of Heteromastus species available in the public database. Molecular results showed distinct genetic differences among these three new Korean species at species level. Comparison of mtCOI gene revealed significant genetic difference between H. filiformis and these Korean species. A comprehensive comparison between three Heteromastus species of present study and their closely related congeners is conducted based on morphological and genetic results.

New species of Caromiobenella Jeon, Lee & Soh, 2018 (Crustacea, Copepoda, Monstrilloida) from Chuja Island, Korea.

Male monstrilloid copepods belonging to the genus Caromiobenella Jeon, Lee & Soh, 2018 were collected from Chuja Island, Jeju, Korea, using a light trap. This paper describes a new species, Caromiobenellaohtsukai sp. n., based on the display of reduced, knob-like fifth legs on the ventral side of the first urosomal somite. A unique combination of male genitalia features and number of caudal setae further confirms its specificity. Molecular analysis based on two partial gene sequences of mitochondrial cytochrome c oxidase subunit I (mtCOI) and 28S ribosomal RNA (28S rRNA) also supports the designation of this species by showing a relevant divergence from known congeners. Caromiobenellaohtsukai sp. n. is the ninth member of this genus and also the ninth monstrilloid reported from Korea.

First use of molecular evidence to match sexes in the Monstrilloida (Crustacea: Copepoda), and taxonomic implications of the newly recognized and described, partly Maemonstrilla-like females of Monstrillopsis longilobata Lee, Kim & Chang, 2016.

Two forms of the monstrilloid copepod, one represented by males, the other by females, were dominant among the monstrilloids collected while sampling zooplankton with a light trap in southern coastal waters of Korea. Morphological examination revealed that the males are conspecific with the previously reported and rather specialized Korean species Monstrillopsis longilobata Lee, Kim & Chang, 2016, hitherto known only from males that have extremely long genital lappets. The females also show several diagnostic features of Monstrillopsis, such as prominent eyes, bilobed fifth legs with the inner lobe unarmed and reduced, and four urosomal somites. In addition, though, these females are extraordinary among all Monstrilloida in that their ovigerous spines are directed ventrally, not posteriorly as in most species or anteriorly as in those assigned to Maemonstrilla. Genetic divergence analyses based on partial mitochondrial cytochrome c oxidase subunit I, complete Internal Transcribed Spacer 1 (ITS1)-5.8S-ITS2, and partial 28S rRNA revealed little or no genetic divergence between the present males and females, thus demonstrating that they are mutually conspecific. The present report (1) provides the first morphological description of female M. longilobata with the proposal of a revised nomenclature for antennular setal armament; (2) presents the molecular evidence for conspecificity of the males and females; and (3) lists several morphological characteristics that are sexually dimorphic in this species, and thus likely also in other monstrilloids. Matters bearing on the validity of the genera Haemocera, Monstrillopsis, and Maemonstrilla are discussed.

A new Notomastus (Annelida, Capitellidae) species from Korean waters, with genetic comparison based on three gene markers.

Notomastus koreanussp. n., collected from the sublittoral muddy bottom of Korean waters, is described as a new species. The Korean new species closely resembles N. torquatus Hutchings & Rainer, 1979 in the chaetal arrangement and the details of abdominal segments, but differs in the position of genital pores and the absence of eyes. DNA sequences (mtCOI, 16S rRNA, and histone H3) of the new species were compared with all the available sequences of Notomastus species in the GenBank database. Three genes showed significant genetic differences between the new species and its congeners (COI: 51.2%, 16S: 38.1-47.3%, H3: 3.7-9.3%). This study also includes a comprehensive comparison of the new Korean Notomastus species with its most closely similar species, based on the morphological and genetic results.

Evolutionary History of Chemosensory-Related Gene Families across the Arthropoda.

Chemosensory-related gene (CRG) families have been studied extensively in insects, but their evolutionary history across the Arthropoda had remained relatively unexplored. Here, we address current hypotheses and prior conclusions on CRG family evolution using a more comprehensive data set. In particular, odorant receptors were hypothesized to have proliferated during terrestrial colonization by insects (hexapods), but their association with other pancrustacean clades and with independent terrestrial colonizations in other arthropod subphyla have been unclear. We also examine hypotheses on which arthropod CRG family is most ancient. Thus, we reconstructed phylogenies of CRGs, including those from new arthropod genomes and transcriptomes, and mapped CRG gains and losses across arthropod lineages. Our analysis was strengthened by including crustaceans, especially copepods, which reside outside the hexapod/branchiopod clade within the subphylum Pancrustacea. We generated the first high-resolution genome sequence of the copepod Eurytemora affinis and annotated its CRGs. We found odorant receptors and odorant binding proteins present only in hexapods (insects) and absent from all other arthropod lineages, indicating that they are not universal adaptations to land. Gustatory receptors likely represent the oldest chemosensory receptors among CRGs, dating back to the Placozoa. We also clarified and confirmed the evolutionary history of antennal ionotropic receptors across the Arthropoda. All antennal ionotropic receptors in E. affinis were expressed more highly in males than in females, suggestive of an association with male mate-recognition behavior. This study is the most comprehensive comparative analysis to date of CRG family evolution across the largest and most speciose metazoan phylum Arthropoda.

Two new species in the genus Phoxokalliapseudes Drumm & Heard, 2011 (Crustacea: Tanaidacea: Kalliapseudidae) from the southwestern and southern coasts of Korea.

Two new species of Phoxokalliapseudes from the southwestern and southern coasts of Korea are described. Phoxokalliapseudes aculeatus n. sp. is distinguished by the two robust spiniform setae on the ventral margin of the cheliped basis, pereonites 2-6 each with a hyposphaenium and small spinules, and the setiferous lobe on the mandibles with different numbers of serrated spiniform setae in the female and male (five and six, respectively). Phoxokalliapseudes cinctus n. sp. can be distinguished by the propodus of the male cheliped with the largest length to width ratio (2.5: 1) of the genus, and the fixed finger with small denticles on the cutting edge and near the insertion of the dactylus. The female has the largest dactylus to propodus length ratio of pereopod 6 in the genus. Only four species of Phoxokalliapseudes have been described or redescribed previously, of which some exhibit morphological differences with the type specimens, possibly indicating additional new species. To minimize identification difficulties caused by morphometric variations in developmental stages, the morphological characteristics of the new species are described in detail for a fixed size range and compared to different-sized individuals. Additionally, a comprehensive comparison of the new Phoxokalliapseudes species with the other known species is provided and discussed.

On the occurrence of caligids (Copepoda: Siphonostomatoida) in the marine plankton: a review and checklist.

Members of the copepod genus Caligus Müller, 1785 (Siphonostomatoida: Caligidae) are commonly referred to as sea lice. Virtually all of the more than 450 species utilize marine fishes as hosts, however, an increasing number of records from marine plankton samples shows that at least some species reside in the water column during their adult phase. Members of three different genera, Caligus, Lepeophtheirus von Nordmann, 1832, and Metacaligus Thomsen, 1949 have been reported from plankton samples off eastern Asia and in the north-western Atlantic. Thirteen species have so far been consistently reported from the plankton only with no information on their hosts. Here we review the various hypotheses previously proposed to explain the presence of caligids in the water column, i.e. accidental occurrence, behavioral detachment from the host during mate location, and host-switching. The discovery of adults of two species of Caligus with no other developmental stages on their teleost hosts, suggests an ontogenetic host-switching after the final molt since both species also occurred in plankton samples. A checklist of all caligid records from the marine plankton, including known host data, is presented.

A new species of Eusirus from Jeju Island, Korea (Crustacea, Amphipoda, Eusiridae).

A new eusirid amphipod, Eusirus bulbodigitussp. n., from Jeju Island, Korea is described with a detailed description and illustrations. Eusirus bulbodigitussp. n. shows common features with the five known eusirid amphipods Eusirus abyssi Stephensen, 1944, Eusirus columbianus Bousfield & Hendrycks, 1995, Eusirus hirayamae Bousfield & Hendrycks, 1995, Eusirus laticarpus Chevreux, 1906, and Eusirus parvus Pirlot, 1934, such as the mandibular palp article 3 bearing a group of setae laterally. However, this new species is differentiated by the combination of the following characteristics: the eyes are poorly developed, the propodus on pereopod 4 is slightly shorter, the inner margin of dactylus on pereopod 4 is swollen, the length of pereopods 5-7 is moderate, the urosomite 1 has a dorsal protrusion distally, and the telson is shallowly cleft. This is the first record of the genus Eusirus Krøyer, 1845 from Korean waters.

Five Sarsiellidae ostracods (Crustacea: Myodocopida) from the South Coast of Korea (East China Sea).

The East China Sea is part of the Warm Temperate Northwest Pacific zoogeographic province and, as such, has a high biodiversity and many tropical and subtropical biotic elements. Nevertheless, many invertebrate groups from this area remain poorly studied. Ostracods are one of them, especially those belonging to the subclass Myodocopa. In this paper we provide the first data on a diverse myodocopid family, Sarsiellidae, not only for the East China Sea, but also for Korea. Five species are reported in this paper from three Korean islands (Jeju, Chuja, and Maemul), and they are only a part of the ostracods collected during this study, indicating a high diversity of the group in this region. Three new species, Eurypylus koreanus sp. nov., Eusarsiella hanguk sp. nov., and Sarsiella nereis sp. nov., clearly stand apart from their respective congeners, mostly by prominent shell characters but also by details of the soft part morphology. Their affinity though clearly indicates a close connection of the region with the more southern zoogeographical realms, especially Central Indo Pacific and partly Temperate Australasia. Two species previously known from Japan (north part of the Sea of Japan and southeastern part of the Pacific Coast of Japan), Sarsiella japonica Hiruta, 1977 and S. misakiensis Kajiyama, 1912, are redescribed. Based on 11 newly obtained COI sequences we construct a preliminary phylogenetic tree, which supports previous hypotheses based on the morphological data, that Eusarsiella Cohen & Kornicker, 1975 is a polyphyletic taxon. With the maps of species distribution provided for each of the three genera, we give an overview of their current zoogeography, and clearly indicate areas that have no data, mostly due to the lack of investigation.

Taxonomic relationship between two Gammarus species, G. nipponensis and G. sobaegensis (Amphipoda: Gammaridae), with description of a new species.

To assess the taxonomic relationship between G. nipponensis and G. sobaegensis, morphological features and molecular phylogenetic relationships using the nuclear 28S rRNA and the mitochondrial COI genes were examined. Detailed morphological observations revealed that G. nipponensis and G. sobaegensis were clearly distinguishable. In addition to the morphological differences, these two species were genetically diverged. In the course of this study, an undescribed species was found from Tsushima and Iki Islands and described here as G. mukudai. In the molecular phylogenetic analyses, monophyletic relationships of G. nipponensis, G. sobaegensis, and G. mukudai were shown but relationships among three species were unclear due to low statistical supports. Phylogeography of G. nipponensis, G. sobaegensis, and G. mukudai were discussed. 

Monogeneans (Platyhelminthes) from marine fishes of Tongyeong, Korea.

Monogeneans (Platyhelminthes) mostly parasitize on fins, skin and gills of fishes. In Korea, the study on monogeneans is limited, although, fishes are frequently encountered with severe infection of monogeneans. Hence, some of ranched and wild fishes were collected from Tongyeong marine living resources research and conservation center, southern part of Korea to screen and understand the infection of monogeneans. All three fish hosts were found with the infection of monogeneans including five species from four different families. They are: (1) Anoplodiscus spari Yamaguti (Publ Seto Mar Biol Lab Kyoto Univ 7:53-88, 1958) (Anoplodiscidae) from the fins and body surface of blackhead seabream Acanthopagrus schlegelii schlegelii (Bleeker); (2) A. tai Ogawa (Fish Pathol 29:5-10, 1994) from the fins of red seabream Pagrus major (Temminck and Schlegel); (3) Benedenia sekii Yamaguti (Studies on the helminth fauna of Japan. Part 19. Fourteen new ectoparasitic trematodes of fishes. Published by the author, Kyoto, 1937), Meserve (Rep Allan Hancock Paci Exped (1932-1937) 2:31-89, 1938) (Capsalidae) from the body surface of P. major; (4) Choricotyle elongata Goto (J Coll Sci Imp Univ Tokyo 8:1-273, 1894) (Diclidophoridae) from the gills of P. major; (5) Udonella fugu Freeman and Ogawa (Int J Parasitol 40:255-264, 2010) (Udonellidae) hyperparasitized on the body of parasitic copepod Pseudocaligus fugu (Yamaguti 1936) (Caligidae) infecting the wild grass puffer Takifugu niphobles (Jordan and Snyder). Capsalids are commonly reported in Korea, except B. sekii, however, other reported genera are uncommon. Hence, all reported monogeneans are considered as a first record from Korea.

Morphological and genetic differentiation of heteromorphy in Labidocera rotunda (Copepoda, Calanoida, Pontellidae).

The pontellid calanoid Labidocera rotunda Mori, 1929 is relatively widespread in the inshore surface waters of East Asia. In this study, some heteromorphic specimens have been observed with extreme morphological discrepancies in the female, including the genital double-somite, the second urosomite, the caudal rami, and the fifth leg. To evaluate the validity of species assignment of the morphological variants, we analyzed the DNA sequences of two mitochondrial genes, 16S rRNA and cytochrome oxidase subunit I (mtCOI). The specimens were collected in the Yellow Sea, the East China Sea and the East Sea (Sea of Japan) around Korea. They differed by <2.9% for mt16S rRNA and by 3.7%-4.7% for mtCOI, suggesting that they are conspecific despite their considerable morphological differences. In contrast, Labidocera japonica Mori, 1935, a morphologically similar species to L. rotunda, displayed interspecific variation of 6.1%-7.2% for mt16S rRNA and 15.1%-16.7% for mtCOI.

Perfluorinated alkyl substances in water, sediment, plankton and fish from Korean rivers and lakes: a nationwide survey.

Water, sediment, plankton, and blood and liver tissues of crucian carp (Carassius auratus) and mandarin fish (Siniperca scherzeri) were collected from six major rivers and lakes in South Korea (including Namhan River, Bukhan River, Nakdong River, Nam River, Yeongsan River and Sangsa Lake) and analyzed for perfluorinated alkyl substances (PFASs). Perfluorooctane sulfonate (PFOS) was consistently detected at the greatest concentrations in all media surveyed with the maximum concentration in water of 15 ng L(-1) and in biota of 234 ng mL(-1) (fish blood). A general ascending order of PFAS concentration of water0.80, p<0.001) were observed between PFOS concentration in blood and liver tissues of both crucian carp and mandarin fish. This result suggests that blood can be used for nonlethal monitoring of PFOS in fish. Overall, the rank order of mean bioconcentration factors (BCFs) of PFOS in biota was; phytoplankton (196 L/kg)

Description of Parvocalanusleei sp. n. (Copepoda, Calanoida, Paracalanidae) in Western Korea, with comments on the taxonomic position of Paracalanusarabiensis Kesarkar & Anil, 2010.

A new species of paracalanid calanoid copepod Parvocalanusleei sp. n., is described from specimens collected in shallow waters of Western Korea. The new species is closely similar to Parvocalanusarabiensis (Kesarkar & Anil, 2010), Parvocalanuscrassirostris (F. Dahl, 1894), Parvocalanuslatus Andronov, 1972, and Parvocalanusscotti (Früchtl, 1923) in having two short terminal spines on the distal segment of the fifth leg and a similar rostrum in the female, but can be readily distinguished from its congeners by the body size, relative length of antennules, segmentation of endopod of leg 1, and pattern of ornamentation of spinules on legs 1 to 4 in the female. The taxonomic position of Parvocalanusarabiensis and the validity of the genus Parvocalanus Andronov, 1970 are also discussed.

Reconstruction of arietellid copepod phylogenetic relationship, with description of a new species of Sarsarietellus (Copepoda, Calanoida, Arietellidae) from Korean waters.

A new species of the genus Sarsarietellus from Korean waters, S. orientalis n. sp. is described based on both sexes. This is very closely related to S. suluensis Ohtsuka, Nishida and Machida, 2005 , but is readily distinguished by the following characteristics: in the female (1) narrow head; (2) nearly symmetrical posterior corners of last pedigerous somite, not extending beyond the genital double-somite; (3) antennary endopod slightly longer than the exopod; (4) nearly equal length of three outer spines and the terminal spine of the exopod of the fifth leg, except for the proximal third outer spine; and in the male the left fifth leg with two whip-like setae on the tip of the second exopodal segment not being rotated outside. Sarsarietellus orientalis is the fourth species of the genus Sarsarietellus, while the male of Sarsarietellus species is the first reported. The habitat colonization of arietellids is reconsidered.