Metapenaeopsis provocatoria owstoni (Decapoda: Penaeidae) is distributed in the waters of Japan, Korea and Taiwan. There is, however, no study available on the population biology of this species to design its sustainable management and conservation protocols. We, therefore, studied for the first time its oocyte development, ovarian maturation, size at sexual maturity and spawning season using samples collected from Kagoshima Bay, southern Japan. Histological observation of ovaries confirmed seven oocyte developmental stages. This species exhibited asynchronous ovarian development, which indicates multiple spawning in a single reproductive season. Ovarian maturity stages were classified into three categories based on the developmental stage of the most advanced oocytes in the ovary: immature, maturing and mature. Females containing oocytes that either had evidence of germinal vesicle breakdown or migrating nucleus were defined as mature. The gonadosomatic index exhibited a positive but gradual relationship with ovarian maturation progression. In contrast, macroscopic staging showed a sharper relationship with histological stages of ovarian maturity, which exposed its potential as a maturity index for M. provocatoria owstoni. The size at sexual maturity was estimated to be 12.8 mm CL, and the spawning season appeared to last from April to December, with May to June being the main part.
A hemiarthrine bopyrid, Quadripediphryxus mayuzumii gen. et sp. nov. (Isopoda: Epicaridea: Bopyridae), is described based on a pair of specimens infesting the ventral surface of the abdomen of a snapping shrimp, Synalpheus streptodactylus Coutière, 1905 (Decapoda: Caridea: Alpheidae). The shrimp was collected from ornamental coral rock of an unidentified species of Poritidae (Cnidaria: Anthozoa) from Ehime Prefecture, Japan. The female of the new genus is similar to those in the genera Hemiphryxus Bruce, 1978, Eriphrixus Markham, 1990, and Micropodiphryxus Boyko, 2012, in having seven and four pereopods on the concave and convex sides of the body, respectively. However, female of the new genus can be distinguished from those in the other genera by the presence of a tiny triangular pleotelson bearing uropods. This finding represents the 12th species of hemiarthrine bopyrids found infesting the abdomen of caridean shrimps recorded from Japan.
A deep-sea isopod, Janirella (Janirella) longicauda sp. nov. (Asellota: Janirellidae), was found off the coast of Iwate Prefecture, west of the Japan Trench, at a depth of 3,370–3,547 m by trawling. Janirella longicauda sp. nov. can be distinguished from other species of Janirella Bonnier, 1896 by their long posterior pleotelson, the size differences between the posterior and anterior lateral processes in the pleotelson, the long and tapered rostrum and lateral processes in the pereonites, and the absence of dorsal spines on the pereonites and pleotelson. As a result of the description of this species, the number of species of Janirella (Janirella) known from NW Pacific becomes 12 species.
A new species of cavernicolous sesarmid crab is described from Vanuatu. Karstarma umbra sp. nov. belongs to a group of three species that has the chitinous distal part of the male first gonopod slender and elongate. The new species can easily be distinguished from K. balicum (from Bali, Indonesia) and K. loyalty (from Loyalty Islands) by its distinctly longer ambulatory legs and its relatively more slender male first gonopod. Karstarma umbra is morphologically closest to K. waigeo (from Indonesian Papua) but has proportionately longer legs and the outer margin of the male first gonopod is distinctly concave. The taxonomy of the genus is discussed and a revised key to the 18 species is provided.
A new species of Bathyceradocus, one of the maerid amphipods, is described based on the specimens collected from sunken wood on the bottom of the Kumano-nada, central Japan. Bathyceradocus japonicus sp. nov. can be distinguished from its congeners by the number of the accessory spines on the pleonite 1, the number of articles on the accessory flagellum, and the strongly oblique palm of the gnathopod 2 with the dentate margin. A brief note on the behavior of the new species and a key to species of the genus are provided.
The cymothoid isopod Ceratothoa oxyrrhynchaena Koelbel, 1879 was collected from the buccal cavity of yellowback sea-bream, Dentex hypselosomus Bleeker, 1854, in the southern Sea of Japan. There was a linear positive relationship between isopod body length (female, 22.6–35.0 mm; male, 9.6–17.0 mm) and fish standard length (115–249 mm). Body lengths of paired female and male isopods were also correlated with each other. These results indicate that isopods parasitized smaller fish than those examined and grew steadily as their hosts grew. This paper also suggests that the isopod can stay over three years in the buccal cavity of fish.
A new species of Hexapinus (Hexapodidae) is described from Hatoma Island, Ryukyu Islands, Japan. Hexapinus patuma, new species, is morphologically close to H. latus Rahayu & Ng, 2014, but can be distinguished by the structures of the carapace and third maxilliped, as well as the degree of setation of ambulatory legs.
An ovigerous female of Nerocila phaiopleura Bleeker, 1857 was collected from the body surface of a Japanese sardine, Sardinops melanostictus (Temminck & Schlegel, 1846) (Clupeidae), caught in Hitachi Port, Ibaraki Prefecture, central Japan. This collection extends the northern distribution limit of N. phaiopleura from Kujukuri, Chiba Prefecture, to Hitachi Port, Ibaraki Prefecture. In Japan, N. phaiopleura has so far been reported from coastal waters of the western North Pacific ranging from southern Kyushu to central Honshu, the East China Sea off Kyushu, and the Seto Inland Sea. While much remains unknown on its distribution in the southern Sea of Japan, N. phaiopleura is found from waters affected by a warm current, the Kuroshio, and its branch, the Tsushima Current. The species has not been found from subtropical waters of the Ryukyu Islands to date. Due to low water temperatures, the species is not likely to occur in subarctic waters affected by a cold current, the Oyashio, and the Kuroshio-Oyashio transition waters off northeastern Japan.
A rare xanthid crab species Cyrtocarcinus truncatus (Rathbun, 1906) is recorded from Ouvéa, Loyalty Islands, New Caledonia, and Ishigaki Island, Ryukyu Islands, Japan. This represents the first record of the species from outside Hawaii. Morphological features and its variations are described in detail.
The caligid copepod Gloiopotes huttoni (Thomson, 1890) was collected from the body surface of a black marlin, Istiompax indica (Cuvier, 1832), in the western North Pacific Ocean off Yonaguni-jima Island, the Ryukyu Islands, southern Japan. This represents the first record of G. huttoni from I. indica in Japanese waters. This copepod is known to use almost exclusively billfishes as its hosts, but due to the past confused billfish taxonomy, the billfish hosts have been recorded using various scientific names, most of which have recently been relegated to junior synonyms. Thus, based on the current taxonomy of billfishes and the literature published between 1890 and 2019, this paper also reviews the hosts and distribution of G. huttoni. Five species of billfishes in two families [black marlin; striped marlin, Kajikia audax (Philippi, 1887); blue marlin, Makaira nigricans Lacépède, 1802; sailfish, Istiophorus platypterus (Shaw, 1792) in the Istiophoridae; and swordfish, Xiphias gladius Linnaeus, 1758 in the Xiphiidae] serve as hosts for G. huttoni in the Pacific and Indian oceans, but four non-billfish species [bigeye tuna, Thunnus obesus (Lowe, 1839); yellowfin tuna, Thunnus albacares (Bonnaterre, 1788); wahoo, Acanthocybium solandri (Cuvier, 1832); and blue shark, Prionace glauca (Linnaeus, 1758)] are regarded as accidental hosts.
An ovigerous female of Lernaeenicus ramosus Kirtisinghe, 1956 was collected from an areolate grouper, Epinephelus areolatus (Forsskål, 1775), in coastal waters of Suruga Bay (western North Pacific Ocean), Shizuoka Prefecture, central Japan. This represents a new host and the easternmost distribution records for L. ramosus. Based on the literature published between 1956 and 2019, this paper tabulates the known hosts and distribution records of the species in the Indo-West Pacific region. The recent collections of L. ramosus from Japan further support a previous suggestion that the geographical distribution of the species in Japanese waters is affected by two warm currents, the Kuroshio, and its branch, the Tsushima Current.
First stage larva of the deep-sea giant shrimp, Sclerocrangon rex is described and illustrated under laboratory conditions. The larvae hatched in the most advanced condition, such as in having stalked eyes, among the congeneric species with abbreviated development. The newly hatched first larvae were staying together by clinging maternal pleopods until the second stage.
Argulus coregoni Thorell, 1864 is briefly described based on specimens from the body surface of amago salmon, Oncorhynchus masou ishikawae Jordan & McGregor, 1925, cultured at a trout farm in Tokushima Prefecture, Shikoku, western Japan. This represents the first confirmed record of A. coregoni from farmed salmonids in Shikoku. A list of occurrence records of A. coregoni from fishes reared in Japan is also provided based on the literature published between 1950 and 2019. The species has so far been reported from three species and two subspecies of salmonids and one species of plecoglossid reared at 14 sites in 10 prefectures (Tochigi, Tokyo, Nagano, Ishikawa, Gifu, Aichi, Wakayama, Hyogo, Tokushima, and Yamaguchi). Most of these sites were governmental or research facilities, and it is evident that little attention has been paid to A. coregoni at commercial tout farms. The species is considered to occur at more trout farms in Japan.