Ko Tomikawa

Phylogenetic Relationships Within the Genus Jesogammarus (Crustacea, Amphipoda, Anisogammaridae) Deduced from Mitochondrial COI and 12S Sequences

Abstract The genus Jesogammarus contains 16 species in two subgenera, Jesogammarus and Annanogammarus. To examine relationships among species in the genus, a molecular phylogenetic study including eight species of the former subgenus and four of the latter was conducted using partial DNA sequences of the mitochondrial COI and 12S rRNA genes. MP, NJ, and ML trees based on the combined COI and 12S data indicated monophyly of the subgenus Annanogammarus, though the monophyly of Jesogammarus was left unresolved. Consistent with few morphological differences, Jesogammarus (A.) naritai and J. (A.) suwaensis showed low genetic differentiation and did not show reciprocal monophyly, which suggests a close affinity of these taxa.

Mineralized rods and cones suggest colour vision in a 300 Myr-old fossil fish

Vision, which consists of an optical system, receptors and image-processing capacity, has existed for at least 520 Myr. Except for the optical system, as in the calcified lenses of trilobite and ostracod arthropods, other parts of the visual system are not usually preserved in the fossil record, because the soft tissue of the eye and the brain decay rapidly after death, such as within 64 days and 11 days, respectively. The Upper Carboniferous Hamilton Formation (300 Myr) in Kansas, USA, yields exceptionally well-preserved animal fossils in an estuarine depositional setting. Here we show that the original colour, shape and putative presence of eumelanin have been preserved in the acanthodii fish Acanthodes bridgei. We also report on the tissues of its eye, which provides the first record of mineralized rods and cones in a fossil and indicates that this 300 Myr-old fish likely possessed colour vision.

Description of a New Species of Sternomoera (Crustacea: Amphipoda: Pontogeneiidae) from Japan, with an Analysis of the Phylogenetic Relationships Among the Japanese Species Based on the 28S rRNA Gene

A new species of amphipod, Sternomoera morinoi Tomikawa and Ishimaru, is described from subterranean aquatic habitats in Shiga Prefecture, Japan. In addition, Relictomoera tsushimana (Uéno, 1971) from a well on the island of Tsushima in Japan is transferred to Sternomoera and redescribed based on the holotype. Sternomoera morinoi sp. nov. is most similar to S. tsushimana (Uéno, 1971) comb, nov., but is distinguished by having many fine setae on the body, a shorter antenna 1, fewer C-setae on mandibular palp article 3, a shorter mandibular palp article 3, sparsely setose anterior margins of coxae 1–4, a different armature of the palmar margins of gnathopods 1 and 2, and no long setae on the posterior margin of the basis in gnathopod 2 and pereopods 3 and 4. The phylogenetic relationships among the Japanese species of Sternomoera are also estimated, based on partial DNA sequences of the nuclear 28S rRNA gene.

A New Freshwater Species of the Genus Jesogammarus (Crustacea: Amphipoda: Anisogammaridae) from Northern Japan

Abstract A new species of anisogammarid amphipod, Jesogammarus (Jesogammarus) mikadoi sp. nov., is described from freshwater habitats in northern Honshu, Japan. The species is distinguished from its congeners by having dorsal setae on pereonites 5–7 and pleonites 1–3.

A New Species of Psammogammarus (Amphipoda: Melitidae) from Kuchinoerabu Island, Japan, with a Note on Its Feeding Habits

A new melitoid Amphipoda, Psammogammarus mawatarii, is described from Kuchinoerabu Island, Kagoshima Prefecture, Japan. This is the first record of the genus from Asia. The new species is morphologically similar to P. garthi, but differs from the latter in the following features: 1) lateral cephalic lobe of head not strongly produced; 2) head lacking antennal sinus; and 3) posteroventral corner of epimeral plate 3 rounded. Morphology of maxillae 1 and 2, and mandible, and gut contents (harpacticoid Copepoda) of P. mawatarii indicate that the feeding type of the species seems to be, at least facultatively, carnivorous.

A revision of Eogammarus Birstein, 1933 (Crustacea, Amphipoda, Anisogammaridae), with a description of a new species

A revision of the genus Eogammarus is made based on type material and on collections from numerous localities. The following eight species are redescribed: E. kygi (Derzhavin, 1923), E. barbatus (Tzvetkova, 1965), E. confervicolus (Stimpson, 1856), E. oclairi Bousfield, 1979, E. psammophilus Bousfield, 1979, E. schmidti (Derzhavin, 1927), E. possjeticus (Tzvetkova, 1967), and E. tiuschovi (Derzhavin, 1927). A new species is described under the name of E. itotomikoae sp. nov. Eogammarus sinensis Ren, 1992 is relegated to a junior synonym of E. possjeticus. Eogammarus turgimanus is transferred into Jesogammarus. In the descriptions of species, special attention is paid to the following characters: the condition of the posterodistal seta on the peduncular article 1 of antenna 1, the number and length ratio of aesthetascs on antenna 1, the setal ornamentation of the peduncular article 1 of antenna 2, the setae ornamentation of the palp article 1 of the maxilla 1, the number of retinacula on the pleopods, and the dorsal condition of pleonites. A key to the species of Eogammarus is provided.

INGOLFIELLA INERMIS N. SR, A NEW INTERSTITIAL INGOLFIELLID AMPHIPOD FROM OKINAWA, SOUTHERN JAPAN (PERACARIDA, AMPHIPODA)

A new ingolfiellid amphipod, Ingolfiella inermis n. sp. is described from a coral sandy beach of Okinawa, southern Japan. The new species differs from its congeners in the following characters: head, pereionites, pleonites, and urosomites without dorsal setae; fleshy and moderately long telson; broad carpus of gnathopod 2 with some minute teeth and long palmar angle spine; dactyli of gnathopods 1 and 2 each with 4 teeth; pereiopod 7 longer than the other pereiopods; uropod 1 longer than uropod 2; outer ramus of uropod 1 longer than 1/2 inner ramus.

A new species of the genus Dulichiella (Amphipoda, Melitidae) from the Ogasawara Islands, Japan

A new amphipod Dulichiella takedai sp. nov. is described from the Ogasawara Islands, Japan, only the second species of the genus from Japan. Dulichiella takedai is morphologically similar to D. appendiculata (Say, 1818) from the USA and D. cuvettensis Appadoo & Myers, 2005 from Mauritius, but D. takedai differs from D. appendiculata in having slender setae on urosomite 1 shorter than the spines, a developed fourth spine of the distolateral crown of larger male gnathopod 2 and the bases and meri of male pereopods 5-7 lacking bunches of long, slender setae. Dulichiella takedai differs from D. cuvettensis in having a minutely serrate posteroventral margin of epimeral plate 3, a short mandibular palp article 3 with more than eight slender setae, and equally developed third and fourth spines on the distolateral crown of larger male gnathopod 2.

Four species of the genus Stephonyx (Crustacea: Amphipoda: Uristidae) from Japan, with description of a new species

Four species including one new species of the genus Stephonyx are described from Japan: Stephonyx perexcavatus sp. nov., Stephonyx biscayensis (Chevreux, 1908), Stephonyx laqueus (Barnard, 1967) and Stephonyx mytilus (Barnard and Ingram, 1990). Stephonyx perexcavatus sp. nov. is distinguished from the congeners by the combination of the following features: dorsal margin of body smooth, posteroventral corner of epimeral plate 1 not pointed, lateral cephalic lobe rounded, article 1 of mandibular palp shorter than 0.5 times article 2, length of carpus of gnathopod 1 longer than 0.75 times propodus, and palm of gnathopod 2 deeply concave. This is the first record of S. biscayensis and S. mytilus from Japan. A key to the species of Stephonyx is provided.

A new species of the genus Pseudocrangonyx (Crustacea, Amphipoda, Pseudocrangonyctidae) from Korea

Abstract A new subterranean species of pseudocrangonyctid amphipod, Pseudocrangonyx daejeonensis sp. n. is described from the interstitial waters in Daejeon, Korea. Pseudocrangonyx daejeonensis sp. n. is distinguished from three morphologically similar congeners, P. coreanus Uéno, 1966, P. febras Sidorov, 2009, and P. gudariensis Tomikawa & Sato, 2016, by the characteristics of antenna 1, antenna 2, mandible, gnathopod 2, pleopods, uropods 1–2, and telson. Molecular phylogenetic analyses based on nuclear 28S rRNA and histone H3, and mitochondrial cytochrome c oxidase subunit I and 16S rRNA genes revealed that P. daejeonensis is a sister species of the unnamed Pseudocrangonyx sp. 3 inhabiting central Japan.