We described the shell microstructure of the cold seep-associated bivalve Conchocele bisecta using the acetate peel method and scanning electron microscopy, and revealed complex microstructural changes with ontogeny. The shell of the bivalve has outer, middle, and inner layers that consist of aragonite. The outer layer consists of spherulites and spindles of various sizes and shapes; these microstructures are identified as spherulitic, planar spherulitic, spherulitic prismatic, and spindle-like structures. The middle layer is characterized by cone complex crossed lamellar structure in the outer part and crossed lamellar structure in the inner part. The inner layer is composed of cone complex crossed lamellar, fine complex crossed lamellar, and irregular prismatic structures.

On the basis of the observations from the umbo to the ventral margin of each shell layer, we recognized two growth stages that are divided by microstructural distributions in the outer and inner layers and the positions of disturbance rings. The early growth stage is characterized by spherulitic structure in the outer layer, cone complex crossed lamellar structure in the inner layer, and scarce disturbance rings. The late growth stage, on the other hand, has specific microstructures (planar spherulitic, spherulitic prismatic, and spindle-like structures) that lie as sheeted layers within the spherulitic structure of the outer layer, and the disturbance rings are situated close to specific microstructures in the outer layer. In addition, alternations between areas that are cone complex crossed lamellar, thin-layered irregular prismatic, and fine complex crossed lamellar structures are observed in the inner layer. The characteristics of both growth stages indicate that shell growth rate is more variable in the late stage than in the early stage, and that growth rate decreases from the early to late stage, possibly caused by a physiological change. This study suggests that it is important to examine shell microstructural distribution to reveal shell growth and life history.

The taxonomy of three Recent Spinileberis species (S. quadriaculeata, S. furuyaensis, S. pulchra) and one new fossil species, S. lubrica sp. nov. from Japan was studied, and the phylogenetic relationship between the four species was also considered. The relationship with S. lubrica sp. nov., which is an extinct species, was analysed by comparing its carapace morphology with those of the three living species. On the basis of the observation of the cross-section of four Spinileberis shells, the crystallographic structure of the valve is similar between S. pulchra and S. furuyaensis, and S. quadriaculeata and S. lubrica sp. nov., respectively. On the other hand, the relative thickness of the valve is variable among the four Spinileberis species. The same number and similar distributional pattern of normal pores between S. lubrica sp. nov. and S. quadriaculeata suggest that S. lubrica sp. nov. evolved from the common ancestor of S. quadriaculeata and S. lubrica sp. nov. A consideration of the characteristics of the new fossil species, together with the three recent ones, leads us to believe that the species of the inner bay of Japan, S. lubrica sp. nov., is likely to have adapted to very fine sand or silt with relatively high-salinity water, in contrast to the other three Spinileberis species. The complete male soft parts of S. furuyaensis are also herein described for the first time.

The internal morphology of the productide brachiopod Anidanthus ussuricus from the Middle Permian of the Takakurayama area, Fukushima Prefecture, Japan, shows an evident pattern of brachial ridges that are identified as a four-lobed ptycholophe of the feeding organ or lophophore. Because a ptycholophe has not previously been identified in productidines, we describe this structure to provide further insight into the morphology of the productide lophophore. A comparison of the lophophores between the productides and the extant thecideoids suggested that during the growth of productides, the disposition of a multilobed ptycholophe requires the development of elevated platform-like ridges or the enlargement of the dorsal valve, both of which provide greater area for the attachment of the lophophore. In contrast, the simple ptycholophe of Anidanthus is located on a faint relief of brachial ridges, which agrees with what has been observed for the thecideoid ptycholophe. Because the productide shell form plays a role in the generation of passive feeding flows, it is expected that the productide feeding system, which supplies the energetic demands of the organism, would develop in response to the interaction between the lophophore and the overall shell form of productides.

Late Cretaceous heteromorph ammonoids, Ainoceras kamuy and Ainoceras paucicostatum, were discovered for the first time from the Futakawa Formation in the Aridagawa area, Wakayama, southwestern Japan. Other molluscan fossils such as Eupachydiscus sp., Gaudryceras aff. striatum, “Gigantocapulus” transformis, Sphenoceramus nagaoi, Sphenoceramus orientalis and Inoceramus balticus also cooccur with Ainoceras, and together they indicate the lower Campanian Stage. Recently, the middle Turonian—Santonian and upper lower Campanian—Maastrichtian litho- and biostratigraphy in the Aridagawa area was established. Therefore, the lower Campanian strata in the study area fill the gap between them and supplement the Upper Cretaceous stratigraphy in the Aridagawa area. The results of this study advance the biostratigraphy and correlation of the marine Cretaceous strata in the northwestern Pacific region.

A reinvestigation of Chilotherium from the Mizunami Group revealed that they do not belong to the genus and comprise two species, Brachypotherium? pugnator and Plesiaceratherium sp. It was found that B.? pugnator is more closely related to the Early Miocene Asian Brachypotherium (B. fatehjangense and B. shanwangensis) than to other species; this is inferred on the basis of the dental characteristics of strongly constricted protocones and prominent antecrochets in upper molars. Plesiaceratherium sp. resembles Pl. gracile rather than other European species in terms of the weak rugosities on the labial walls of the P_2–3. The assemblage of rhinoceros fossils of the Mizunami Group is very similar to that of the Early Miocene Shanwang Fauna in China.

We review the entelodontid artiodactyl fauna of the upper Eocene Ergilin Dzo Formation in southeastern Mongolia. Also, we describe new specimens of Brachyhyops trofimovi from the Khoer Dzan locality and review the characteristics and Asian distribution of Brachyhyops. The revised entelodontid fauna of the formation consists of three species: Entelodon gobiensis (from the Khoer Dzan and Ergilin Dzo localities), Brachyhyops trofimovi (from the Khoer Dzan locality), and Brachyhyops? sp. (from the Ergilin Dzo locality). The discovery of p4 and M2 of B. trofimovi demonstrates the definitive diagnostic characteristics of this species within the genus: p4 is buccolingually wide and is triangular in occlusal view; it has a well developed and high cusp (= hypoconid?), which is fused to the posterior part of the protoconid; and M2 has a better-developed pericone. In Asia, Brachyhyops is recorded only in the southern part during the middle Eocene and only in the northern part during the late Eocene, implying that the genus originated in the southern part of Asia and subsequently migrated northward, giving rise to northern Asian and North American Brachyhyops.

A total of 145 ostracode taxa were obtained from the upper part of the Plio—Pleistocene Takanabe Formation, Miyazaki Group, in the northern part of the Miyazaki Plain, Southwest Japan. Most of the assemblages are extant temperate and subtropical water species that have been reported from the recent western North Pacific Ocean around Southwest Japan, the Tsushima Strait, and the shelves off China. Four ostracode bioassociations (UA, MA, LA, and DA) and two biofacies (SF and DF) were discriminated on the basis of Rand Q-mode cluster analyses. Biofacies SF is divided into six sub-biofacies (SF1–6). The results revealed at least two transgressions and one regression during the deposition of the upper part of the Takanabe Formation. The sea-level fluctuation at approximately 2.6 Ma inferred in this study is extremely large compared with the glacio-eustatic sea-level fluctuations during the late Pliocene to early Pleistocene, suggesting that local tectonic movement in the study site during the deposition of the upper part of the studied interval at ∼2.6 Ma may have led to the large sea-level fluctuation. This paper also includes descriptions of two new species, Acanthocythereis abei sp. nov. and Acanthocythereis takanabensis sp. nov.