Japanese Waters Research Articles

Diving deeper into the taxonomy of the Neoscopelus species complex (Myctophiformes: Neoscopelidae) with the description of Neoscopelus serranoi sp. nov.

Previous studies have highlighted possible cryptic biodiversity in the genus Neoscopelus. This hypothesis was tested using new morphological, molecular and biogeographical data on species of this genus caught in the north Atlantic between 2010 and 2022. The information obtained has been combined with available data in an integrative approach, including a review of morphological characters reported in the ichthyological literature and DNA-based species delimitation analyses. The main outcome of the present study is the description of Neoscopelus serranoi sp. nov. from the Atlantic and southwestern Indian Oceans. The new species is morphologically very similar to Neoscopelus microchir from which differs in having a shorter anal-fin base, a shorter pelvic fin, more dorsal and pectoral-fin rays, less anal-fin rays, fewer gillrakers and fewer isthmus and lateral photophores. They also differ in geographic distribution, with the new species occurring in the Atlantic Ocean and the near southwestern Indian Ocean, whereas N. microchir was originally described from Japanese waters of the Pacific Ocean. A literature review of available morphological data between geographic areas for Neoscopelus macrolepidotus and Neoscopelus microchir showed a large intraspecific overlap and no boundaries. However, molecular species delimitation based on the mitochondrial COI gene revealed the existence of cryptic diversity in both species, with eight to ten molecular operational taxonomic units (MOTU), compared to three valid species. Neoscopelus serranoi sp. nov. was considered an independent MOTU in all analyses performed, supporting the morphological identification as a new species. These results highlight that the taxonomy of Neoscopelus is far from settled and show that a greater sampling effort is needed to resolve the uncertainties and to describe unknown putative species. This also exemplifies the virtues of integrative taxonomy in delving into the systematics of deep-sea fishes.

First record of Phoronopsis (Phoronida) from Japan, with a description of Phoronopsiscalifornica Hilton, 1930 from Okinawa.

Phylum Phoronida currently contains two genera, Phoronis Wright, 1856 and Phoronopsis Gilchrist, 1907, with approximately thirteen speices. Phoronida is distributed worldwide, ranging from northern Europe to southern New Zealand and also from intertidal to 400 m depths. From Japanese waters, four species of Phoronis have been reported, viz. Phoronisijimai Oka, 1897, Phoronisaustralis Haswell, 1883, Phoronispsammophila Cori, 1889 and Phoronisemigi Hirose et al., 2014. We describe the morphology of Phoronopsiscalifornica Hilton, 1930, based on five specimens collected at a sandy-mud habitat in Nago Bay and Oura Bay, Okinawa, Japan. We examined the internal anatomy by serial paraffin sections. We also examined the genetic distance of Japanese specimens from the other phoronid sequences in GenBank. This is the first record of Phoronopsis from Japanese waters and the fifth species record of phoronids in addition to the previously recorded four species of Phoronis.

Anisakid larvae in the skipjack tuna Katsuwonus pelamis captured in Japanese waters: Two-year monitoring of infection levels after the outbreak of human anisakiasis in 2018

In 2018, human anisakiasis caused by the ingestion of the skipjack tuna Katsuwonus pelamis occurred frequently in Japan. This may be attributable to a heavy infection of A. simplex (s.s.) in the host's muscle tissue. In this study, we investigate infection levels of anisakid L3 larvae in skipjack tuna captured in Japanese waters afterward (2019–2020) to contribute to predict and prevent the outbreak of human anisakiasis. A total of 476 larvae were detected from 78 out of 85 skipjack tuna captured at 14 stations of the Pacific and East China Sea. The present parasitological survey suggests that infection levels in 2019–2020 were low, comparing that in 2018; in total only seven larvae were found from the host's muscle tissue. The collected larvae were identified by molecular methods to Anisakis berlandi, A. pegreffii, A. simplex (s.s.), A. typica and Skrjabinisakis physeteris (s.l.). Not only larvae of A. simplex (s.s.) but also those of A. berlandi were found from the muscle tissue and thus the latter species may also be a causative agent of human anisakiasis. In addition, this study confirmed the geographic distribution pattern that A. simplex (s.s.) is abundant in the Pacific, while A. pegreffii is dominant in the East China Sea. Our results contribute to understanding the risk of food poisoning and stock delimitation of host animals.

A new hermit crab species of the genus Catapaguroides A. Milne-Edwards & Bouvier, 1892 (Decapoda: Anomura: Paguridae) from Okinawa Island, southwestern Japan

Catapaguroides ngankeeae n. sp., a new diminutive species of Paguridae, is described from shallow reef environments in Okinawa Island, Ryukyu Islands, southwestern Japan. The new species is morphologically similar to C. brevidactylus Komai & Rahayu, 2013 and C. melini de Saint Laurent, 1968, but is distinguished from the two species primarily by the ornamentation of the palm and dactylus of the right cheliped and the length of the right sexual tube in the male. Catapaguroides ngankeeae n. sp. represents the eleventh species of the genus from Japanese waters.

Pseudarchasteridae (Asteroidea: Paxillosida) in Japanese waters, with description of a new species and range extension of three species

ABSTRACT Four Pseudarchasteridae species, including one new species, are described from Japanese waters. Paragonaster hoeimaruae Kobayshi sp. n. resembles two north-west Pacific congeners, P. chinensis and P. obtusus, but differs from these species in having pedicellariae and lateral abactinal series extending to less than one-half of arm length. We also report the first occurrence of Gephyreaster and P. stenostichus from Japanese waters. http://www.zoobank.org/urn:lsid:zoobank.org:pub:0B02F074-9B9A-4A87-A9D5-797740C6EE50

Myxobolus acanthogobii Hoshina, 1952 and Myxobolus selari n. sp. (Myxosporea: Myxobolidae) infecting brain of commercial fishes in Terengganu, Malaysia.

Myxosporean infection in marine water fishes has drawn less attention than in freshwater fishes, which resulted in a higher taxonomic variety in freshwater in Malaysia. This study aimed to address the gap by conducting a myxosporean survey on two commercially significant marine fish species, Nemipterus furcosus (Valenciennes) (Eupercaria incertae sedis: Nemipteridae) and Selar crumenophthalmus (Bloch) (Carangiformes: Carangidae), collected from the northeastern part of peninsular Malaysia. During the examination of the organs, two distinct Myxobolus Bütschli, 1882 species were discovered in the brain tissue of these fishes, despite the absence of any observable pathological signs. The two Myxobolus species were characterized through morphometry, morphology, and analysis of partial small subunit ribosomal RNA (18S rDNA) gene. As a result, Myxobolus acanthogobii Hoshina, 1952, which infects 2.3% of N. furcosus, is synonymous with a myxobolid species commonly found in Japanese waters, based on its morphological traits, tissue tropism, and molecular diagnostics. Furthermore, a novel species, Myxobolus selari n. sp., was described, infecting the brain of one (11%) individual S. crumenophthalmus. This unique species displayed distinctive features, placing it within a well-supported subclade primarily comprising brain-infecting myxobolids. Maximum likelihood analysis further revealed the close relationships among these brain-infecting myxobolids, underscoring the significance of tissue tropism and host taxonomy for myxobolids. This study represents the initial documentation of Myxobolus species within the southern South China Sea, shedding light on the potential diversity of marine myxosporean in this region. This article was registered in the Official Register of Zoological Nomenclature (ZooBank) as urn:lsid:zoobank.org:pub:7C400E35-7CB8-4DEE-92B7-F75FF3926441.

A new shallow water species of the palaemonid shrimp genus Palaemon Weber, 1795 (Decapoda: Caridea) from Japan

During a survey of the shallow water decapod fauna in the Miura Peninsula, Kanagawa Prefecture, central Japan, four specimens of a new palaemonid shrimp, Palaemon parvibrachium n. sp., were collected from sea grass beds of Nanozostera japonica (Ascherson & Graebner) Tomlinson & Posluszny, 2001. The new species appears morphologically similar to P. serrifer (Stimpson, 1860), one of the most common representatives of Palaemon Weber, 1795 in Japanese waters, but the short carpus of the second pereopod and the different live colouration readily differentiate the new species from the latter. A DNA barcode (a partial fragment of the mitochondrial CO1 gene), as well as a partial fragment of the mitochondrial 16S rRNA gene, are provided to genetically characterize the new species.

HOST SWITCHING IN DICYEMIDS (PHYLUM DICYEMIDA).

Dicyemids (phylum Dicyemida) are the most common and most characteristic endosymbionts in the renal sacs of benthic cephalopod molluscs: octopuses and cuttlefishes. Typically, 2 or 3 dicyemid species are found in a single specimen of the host, and most dicyemids have high host specificity. Host-specific parasites are restricted to a limited range of host species by ecological barriers that impede dispersal and successful establishment; therefore, phylogenies of interacting groups are often congruent due to repeated co-speciation. Most frequently, however, host and parasite phylogenies are not congruent, which can be explained by processes such as host switching and other macro-evolutionary events. Here, the history of dicyemids and their host cephalopod associations were studied by comparing their phylogenies. Dicyemid species were collected from 8 decapodiform species and 12 octopodiform species in Japanese waters. Using whole mitochondrial cytochrome c oxidase subunit 1 (COI) sequences, a phylogeny of 37 dicyemid species, including 4 genera representing the family Dicyemidae, was reconstructed. Phylogenetic trees derived from analyses of COI genes consistently suggested that dicyemid species should be separated into 3 major clades and that the most common genera, Dicyema and Dicyemennea, are not monophyletic. Thus, morphological classification does not reflect the phylogenetic relationships of these 2 genera. Divergence (speciation) of dicyemid species seems to have occurred within a single host species. Possible host-switching events may have occurred between the Octopodiformes and Decapodiformes or within the Octopodiformes or the Decapodiformes. Therefore, the mechanism of dicyemid speciation may be a mixture of host switching and intra-host speciation. This is the first study in which the process of dicyemid diversification involving cephalopod hosts has been evaluated with a large number of dicyemid species and genera.

Glypturus ferox, a new species of ghost shrimp (Decapoda: Axiidea: Callichiridae) from the Ryukyu Islands, southwestern Japan

The callichirid ghost shrimp genus Glypturus Stimpson, 1866 was represented until now by four extant species world-wide. Only G. armatus A. Milne-Edwards, 1870 is known from the western Pacific. In this study, we describe G. ferox n. sp. based on seven specimens collected from the Ryukyu Islands, southwestern Japan. All specimens of the new species were collected in inner reef lagoons by suction pump. The new species is easily distinguished from all other congeners, including fossil taxa, by having a row of spines on the lower margin of the major cheliped palm. Molecular phylogenetic analysis using the mitochondrial 16S rRNA gene suggests that G. ferox n. sp. is sister to G. armatus; the genetic divergence between the two species is high. An identification key to extant species of Glypturus is provided. A brief overview on Japanese species of Callichiridae is also provided. Glypturus ferox n. sp. is the nineth species of the family known from Japanese waters with certainty.

Charting and analyzing the catch distribution of Japan’s coastal fisheries resources based on centennial statistics

Spatiotemporal changes in catches and transition of fishing grounds have been observed in various coastal fishery resources in Japanese waters in recent years. Are these changes part of cyclical fluctuations on a centennial timescale? Are these changes situations that have never been observed prior to this? Are common factors included in the long-term fluctuations among coastal fisheries resources? A total of 12 important Japanese coastal fisheries resources including fishes, shells, invertebrates, and algae were analyzed using fisheries statistics on the geographical center of catch compiled since 1894. The time series of the geographical center of catch showed a cyclical fluctuation trend over time rather than changing monotonically. The geographic center of catch in recent years (2019–2021) was located at the northeastern margin of the distribution, compared to its location since the end of the 19th century for many fishery resources. For coastal fishery resources, the situation in terms of fluctuations in the geographical center of catch is more extreme than in the past 100 years. The results of the dynamic factor analysis suggested that the state of these resources may be affected by the global ocean environment and other factors including human activities. Examining how fisheries have responded to past cyclical fluctuations may provide insight into adapting to the current rapid changes caused by climate change.

Lepocreadiidae (Trematoda) associated with gelatinous zooplankton (Cnidaria and Ctenophora) and fishes in Australian and Japanese waters

We examined gelatinous zooplankton from off eastern Australia for lepocreadiid trematode metacercariae. From 221 specimens of 17 species of cnidarian medusae and 218 specimens of four species of ctenophores, infections were found in seven cnidarian and two ctenophore species. Metacercariae were distinguished using cox1 mtDNA, ITS2 rDNA and morphology. We identified three species of Prodistomum Linton, 1910 [P. keyam Bray & Cribb, 1996, P. orientale (Layman, 1930), and Prodistomum Type 3], two species of Opechona Looss, 1907 [O. kahawai Bray & Cribb, 2003 and O. cf. olssoni], and Cephalolepidapedon saba Yamaguti, 1970. Two species were found in cnidarians and ctenophores, three only in cnidarians, and one only in a ctenophore. Three Australian fishes were identified as definitive hosts; four species were collected from Scomber australasicus and one each from Arripis trutta and Monodactylus argenteus. Transmission of trematodes to these fishes by ingestion of gelatinous zooplankton is plausible given their mid-water feeding habits, although such predation is rarely reported. Combined morphological and molecular analyses of adult trematodes identified two cox1 types for C. saba, three cox1 types and species of Opechona, and six cox1 types and five species of Prodistomum of which only two are identified to species. All three genera are widely distributed geographically and have unresolved taxonomic issues. Levels of distinction between the recognised species varied dramatically for morphology, the three molecular markers, and host distribution. Phylogenetic analysis of 28S rDNA data extends previous findings that species of Opechona and Prodistomum do not form monophyletic clades.

Redescription and first Japanese seamount record of Stethopristes eos (Zeiformes; Parazenidae).

During a biodiversity survey conducted in 2020, focusing on seamounts located in the southern region of Japan, specifically designated as marine protected areas, a single specimen of Stethopristes eos Gilbert, 1905 measuring 124.2 mm in standard length was obtained via the use of a remotely operated vehicle (ROV). The collection occurred at a depth of 519 meters on the Ritto Seamount, located along the western Mariana Ridge. However, this species is poorly known, with only a limited dataset available concerning its morphology. In this study, we present a comprehensive redescription of the species, utilizing information obtained from the type specimens and a newly discovered specimen from Japanese waters. The Japanese specimen constitutes the first recorded occurrence of this species within the western Pacific Ocean. As part of this redescription, we suggest new standard Japanese names for both the genus and species.

First occurrence of ophiuroid-parasitic genus Ophieulima (Mollusca: Gastropoda: Eulimidae) in the North Pacific Ocean

Abstract A eulimid gastropod of the genus Ophieulima, parasitic on the disc of the ophiactid brittle star Ophiactis dyscrita, was collected from 256–343 m deep off Kanagawa, central Japan. This represents the first record of the genus from Japanese waters and even from the North Pacific Ocean. Here we describe it as Ophieulima yoshiharai n. sp. The generic assignment is justified by its conchological characters including (1) a small, conical shape with convex teleoconch whorls, (2) many fine growth lines and some strong growth pause scars on the teleoconch, (3) a well-developed, twisted columella, and (4) a multispiral, brownish transparent protoconch. Ophieulima yoshiharai n. sp. is distinguishable from the three (two named and one undescribed) extant, as well as two fossil congeners by its slender shell with the length of 2.1 times larger than width, a small aperture and a protoconch of 3.5 whorls. The new species is also characterized by its bathymetric distribution, which is shallower than the extant species of Ophieulima. On the other hand, the hosts of Ophieulima species are so far restricted to ophiuroids of the genus Ophiactis and the three named species have mostly been found attached to the lateral and/or dorsal sides of the host's disc, suggesting their similar parasitic ecology.

Description of a new Luidia species (Asteroidea: Paxillosida: Luidiidae) from Japan with molecular phylogenetic analysis of the genus Luidia

Abstract Luidia iwakiensis n. sp. (Asteroidea, Echinodermata) is described in Japanese waters. A molecular phylogenetic analysis including 18 Luidia species supported Döderlein L (1920, Siboga Expedition 4, 193–291) four morphogroups. Morphological reconsideration revealed three of the eight criteria of the morphogroup adopted by Döderlein were justified, but the remaining five characters were rejected. The placement of the new species in the Ciliaris-group was supported by molecular as well as morphological evidence, however, it varies from other species of Ciliaris-group by arm number, length of major inferomarginal spines, and pedicellariae on actinal plates.

Reproductive biology and sperm storage characters in two bobtail squid species (Cephalopoda: Sepiolidae)

Abstract Bobtail squids (Family Sepiolidae) have a variety of sperm storage patterns, but their reproductive biology has not been studied in many species, especially those in Japanese waters. Two species, Austrorossia bipapillata (Subfamily Rossiinae) and Sepiolina nipponensis (Subfamily Heteroteuthinae) inhabit Suruga Bay in Japan. These were sampled approximately bimonthly by trawling at around 500 m between the end of September, 2020 and May, 2022. They were measured for body size (dorsal mantle length) and weighed for gonadosomatic index (GSI) calculation, and their sperm storage mechanism was investigated. The reproductive season occurs from May to October in A. bipapillata and from December to February in S. nipponensis. In both species, spermatangia were deposited inside the mantle cavity as implanted spermatangia. In A. bipapillata, 5.7 ± 6.5 spermatangia were deeply implanted in the opening of the oviduct, and in S. nipponensis 62.7 ± 61.5 spermatangia were attached to the left gill and surface of the connective-tissue capsule enclosing the digestive gland. The GSI was lower and there were fewer spermatophores stored in the spermatophoric sac of A. bipapillata males compared to S. nipponensis, leading us to suggest that it is exposed to weaker sperm competition than S. nipponensis, irrespective of similar sperm storage mechanism in the two species.

Miocene sponge assemblages in the face of the Messinian Salinity Crisis-new data from the Atlanto-Mediterranean seaway.

The Messinian Salinity Crisis is considered as one of the most influential Cenozoic events that impacted negatively on the benthic fauna of the Mediterranean area. Changing environmental conditions, including a sharp reduction of water exchange between the Mediterranean Sea and the Atlantic Ocean, altered the geographical ranges of many organisms, including sponges (Porifera). Here, we report a unique assemblage of isolated sponge spicules from the upper Miocene of southwestern Spain. The newly recognized sponge fauna was inhabiting the Guadalquivir Basin-the corridor between the Mediterranean and the Atlantic Ocean at that time. It represents a taxonomically rich sponge community that consisted of members of "soft" and "lithistid" demosponges and hexactinellids. Demosponges are represented by at least thirty-four taxa, while hexactinellids are significantly rarer; only six taxa have been identified. From among eighteen taxa recognized to the species level, at least eight seem to be inhabiting this area to these days; six are recorded from adjacent areas, such as the Western Mediterranean, South European Atlantic Shelf, and the Azores, and three are present in the Red Sea and/or the Northern Atlantic. Intriguingly, some taxa seem to have their closest relatives in distant areas, such as the Indo-Pacific and Japanese waters which suggests that the range of some once widely-distributed populations shrunk after the isolation of the Mediterranean and the Messinian Salinity Crisis, surviving to the present day only in refugia.

A new species of free-living marine nematode, Fotolaimus cavus sp. nov. (Nematoda, Oncholaimida, Oncholaimidae), isolated from a submarine anchialine cave in the Ryukyu Islands, southwestern Japan

Fotolaimus cavussp. nov. was described from a submarine anchialine cave called Akuma-no-yakata on the Shimoji Island, Miyako Island Group, Ryukyu Islands, southwestern Japan. This is the first free-living marine nematode isolated from a submarine cave in Japan, and the third species of the genus Fotolaimus. This new species differs from its congeners by its small body size, wide amphids, long buccal cavity, long conico-cylindrical tail, and proximally curved gubernaculum. We provide amended dichotomous keys to genera in the subfamily Oncholaiminae and species in Fotolaimus. We also analyzed partial DNA sequences encoding ribosomal small subunit RNA and cytochrome c oxidase subunit I from Fotolaimus cavussp. nov. and six other species of Oncholaimidae collected from Japanese waters. The phylogenetic tree based on the ribosomal small subunit RNA sequences using maximum likelihood analysis suggested a close relationship between Fotolaimus and Wiesoncholaimus as well as Oncholaimus. The topology of the tree was similar to those from previous studies; however, it suggested a new phylogenetic position of Adoncholaimus as a sister clade for Viscosia and Oncholaimus.

Clarification of the identity of deep-sea crab Tymolus uncifer (Ortmann, 1892) and validation of Tymolus melanommus (Doflein, 1904) (Decapoda: Brachyura: Cyclodorippidae).

Examination of material from Japanese waters has disclosed that two species have been confounded under Tymolus uncifer (Ortmann, 1892) (Decapoda: Brachyura: Cyclodorippidae) in previous literature. The identity of Tymolus uncifer sensu stricto is clarified in reference to the lectotype, and the second taxon is herein attributed to T. melanommus (Doflein, 1904), which was originally recognised as a forma of T. uncifer with one specimen from off Kenya and one specimen from Japan. A lectotype is herein selected for T. melanommus in the interest of nomenclatural stability. Differentiating characters between the two species are assessed in detail, and those two species are compared also with T. glaucommus (Alcock, 1894), T. similis (Grant, 1905), T. brucei Tavares, 1991, T. daviei Tavares, 1997, T. hirtipes Tan & Huang, 2000 and T. globosus Spiridonov & Trkay, 2007, all of them are considered as valid. Sexual dimorphism and ontogenetic variation are seen in the relative length and stoutness of the pereopods 2 and 3 in T. uncifer and T. melanommus, but the morphometric characters derived from the two pereopods are useful as diagnostic at comparison between same sex in adults. Comparison of partial fragments of the mitochondrial COI and 16S rRNA gene sequences strongly supports that the two taxa are distinct. Previous records of T. uncifer, including fossil records, are reviewed based on the present findings. Tymolus uncifer and T. melanommus are restricted to Japanese waters at present.

The Abyssal Parasitic Flatworm Fecampia cf. abyssicola: New Records, Anatomy, and Molecular Phylogeny, with a Discussion on Its Systematic Position.

AbstractThe order Fecampiida, a group of parasitic turbellarians, has been poorly studied in terms of its species diversity, morphology, and ecology. Fecampiida is positioned within the monophyletic clade Adiaphanida, along with Tricladida and Prolecithophora, but their phylogenetic relationships are not well understood. Although the nervous and muscular systems of only two species in Fecampiida have been studied, recent research inferred morphological similarities between Fecampiida and Prolecithophora. In this study, we collected fecampiid cocoons and juveniles at depths of 1861-4438 m in Japanese waters. We identified the species on the basis of swimming juvenile specimens and by using histological and molecular methods, while we also examined its musculature and nervous system. Our study revealed a more complex nervous system than previously reported, with dorsal, lateral, and ventral pairs of longitudinal nerve cords connected through an anterior neuropile and posterior transverse commissures. While the nervous and muscular morphology suggested similarities with Prolecithophora, our phylogenetic analysis did not support a close relationship between Fecampiida and Prolecithophora.

Detections of biological sounds and mapping of acoustic presence of marine organisms

Many species of marine organisms have been known to produce sounds, which represents species or family characteristics. Passive acoustic monitoring is widely applied for the monitoring of presence and distribution of marine mammals since the species-specific sound characteristics are well identified. In the present study, sounds of damselfish, silver croaker as well as biosonar sounds of high frequency cetacean and impulse sounds potentially produced by snapping shrimp were extracted from towed and fixed passive acoustic monitoring systems off Japanese waters. Results show the scattered spots of damsel fish in a coral reef and dense aggregation of silver croakers in specific area. Acoustic distribution of silver croakers and finless porpoises was similar each other that suggested co-existence of prey and predator in highly productive area due to river discharge. Pulse sounds distribution was different from others. Towed passive acoustic monitoring provided snap shot acoustic distributions of multiple species. Day-by-day change of acoustic distribution recorded by fixed passive acoustic monitoring systems could be used for the adaptive management of marine organisms.