Takenori Sasaki

The University of Tokyo | Todai

The paper nautilus or greater argonaut, Argonauta argo, is a species of octopods which is characterized by its pelagic lifestyle and by the presence of a protective spiral-shaped shell-like eggcase in females. To reveal the genomic background of how the species adapted to the pelagic lifestyle and acquired its shell-like eggcase, we sequenced the d...

The patellogastropod limpet genus Nipponacmea is widely distributed in Japan and adjacent East Asia. Species identification within Nipponacmea is challenging due to the high variation in shell morphology. In this study, we examined the taxonomy of this genus represented by nine nominal species from 43 localities (including type localities). Results...

The paper nautilus, Argonauta argo , also known as the greater argonaut, is a species of octopods distinctly characterized by its pelagic lifestyle and by the presence of a spiral-shaped shell-like eggcase in females. The eggcase functions by protecting the eggs laid inside it, and by building and keeping air intakes for buoyancy. To reveal the gen...

The Argonaut octopus, commonly called the paper nautilus, has a spiral-coiled shell-like eggcase. As the main characteristics, the eggcase has no internal septum, is composed entirely of calcite with chitosan being the main polycarbonate and is reportedly formed by organic materials secreted from the membranes of the arms. Meanwhile, the biomineral...

The Pacific limpet Cellana nigrolineata is one of the most commonly found limpets in the intertidal shores of Japan. Here, we report the full mitogenome sequence of an individual specimen of the species, which was collected from the intertidal rocky beach in the Nada beach of Gobo City, Wakayama, Japan (33.8316 N, 135.1751 E), in 2018. The sequence...

The pelagic snail Limacina helicina Phipps, 1774 is widely distributed in high-latitude seas and is a sensitive bioindicator of ocean acidification. It is known that the response patterns to ocean acidification differ among populations within or among species. Thus, it is important to understand their genetic population structure and identify the c...

DNA barcoding is an effective and powerful tool for taxonomic identification and thus very useful for biodiversity monitoring. This study investigated the usefulness of the mitochondrial 12S-rRNA gene for the DNA barcoding of shelled marine gastropods. To do so, we determined partial 12S-rRNA sequences of 75 vouchered museum specimens from 69 speci...

Despite being a member of the shelled mollusks (Conchiferans), most members of extant cephalopods have lost their external biomineralized shells, except for the Nautiloids. Here, we report the result of our study to identify major Shell Matrix Proteins and their domains in the Nautiloid Nautilus pompilius , in order to gain a general insight into t...

Higher systematics and evolutionary history of Protobranchia, a subclass of Bivalvia, have long been controversial due to paucity of prominent shell characters and difficulties in collecting live material for diverse taxa. Here, we evaluate the reliability of shell microstructure for protobranch higher systematics by reconstructing a molecular phyl...

Background and aims: Domatia are plant structures within which organisms reside. Callicarpa saccata (Lamiaceae) is the sole myrmecophyte, or 'ant plant', which develops foliar (leaf-borne) myrmeco-domatia in this genus. In this work, we examined domatium development in C. saccata to understand the developmental processes behind pouch-like domatia....

Pectinodontid limpets are important members of deep-sea hot vents and cold seeps as can be seen by their conspicuous presence in both extant and extinct systems. They have traditionally been classified into different genera and species based on shell and radula characteristics; the reliability of these characters has been questioned but not tested...

Molluscan shells exhibit a wide variety of color tones and patterns that are thought to increase fitness in different natural habitats. However, the chemical aspects of shell pigments have not been well understood. We studied the chemical basis of molluscan shell colors via resonance Raman microspectroscopy using a 514.5‐nm laser on six gastropod,...

Recently, the species richness of provannid gastropods inhabiting chemosynthetic ecosystems in the northwestern Pacific has been reassessed, revealing a much higher diversity than previously realized. Here, we describe four further new species, two in the genus Desbruyeresia and two in the genus Provanna. Their generic placement was confirmed by bo...

Elasmobranch fossils have been found from the upper part of the Late Cretaceous Tamagawa Formation（Turonian- Santonian/Coniasian）of the Kuji Group, Iwate Prefecture, Northeast Japan. Teeth belonging to Cretoxyrhinidae（Cretalamna）, Mitsukurinidae（Scapanorhynchus）, Odontaspididae, and Sclerorhynchidae were identified. All of these elasmobranch fossil...

Three-dimensional (3D) reconstruction is an essential approach in morphological studies in biology and paleontology. Seeking an optimized protocol for nondestructive observations, we attempted 3D visualization of various molluscan shells and animals with X-ray micro-computed tomography (micro-CT). Calcified parts of molluscs were easily visualized...

Cyclical ontogenetic changes of shell microstructures have been observed in the subfamily Anadarinae (Mollusca: Bivalvia, Arcidae) including fossil taxa. The changes in the bloody clam Scapharca broughtonii are controlled by temperature, which fluctuates seasonally, and can be used to determine the age of the individuals and to reconstruct paleoenv...

Background Gastropods of the genus Provanna are abundant and widely distributed in deep-sea chemosynthetic environments with seven extant species described in the northwestern Pacific. Methods We investigated the population history and connectivity of five Provanna species in the northwestern Pacific through population genetic analyses using parti...

List of DNA sequences obtained in the present study

Cochlear morphology has been regarded as one of the key traits to understand the origin and evolution of echolocation in bats, given its functionality and performance for receiving echolocation sonar. While numerous researchers have compared adult-stage morphology, few have studied the prenatal development of the cochlea. Here, we provide the first...

Due to increasing anthropogenic impacts on deep-sea hydrothermal vent ecosystems, it is essential to understand population structure and maintenance through larval recruitment and recovery of vent faunas after disturbances. In this study, we quantified vent animal recruitment in the Okinawa Trough, in the western Pacific Ocean. This is the first st...

The genetic diversity of one of the most abundant species in the Arctic and subarctic oceans, the pelagic snail Limacina helicina, has not yet been characterized in the north Pacific. This species has different â €? forma' (L. helicina forma helicina, acuta, pacifica and ochotensis), but whether or not the morphological differences between these fo...

Molluscan shells display a wide variety of pigmentation patterns. The diversity in molluscan shell color reflects the variety of different chemical species in the shell surface. Chemical characteristics of molluscan shell pigments have been extensively investigated, and compounds including porphyrins, polyenes, and melanins were identified as shell...

A group of small lottiid species in Japan, the Lottia kogamogai complex, was phylogenetically analyzed based on the mitochondrial COI gene. As a result, L. kogamogai is subdivided into two geographic clades. Lottia kogamogai s.s. is limited to southern temperate Japan. The northern population formerly considered an intraspecific variation of the sp...

To achieve a better understanding of the formation and evolutionary history of molluscan shell microstructures, we analysed crystallographic textures of shell microstructures of selected species of Protobranchia, the most ancient group of Bivalvia. Our dataset covers four of the five protobranch superfamilies. Shell layers of five species of Nuculo...

The first morphological observation of a euryalid brittle star, Asteronyx loveni, using non-destructive X-ray micro-computed tomography (µCT) was performed. The body of euryalids is covered by thick skin, and it is very difficult to observe the ossicles without dissolving the skin. Computed tomography with micrometer resolution (approximately 4.5–1...

Figure S3

Aragonite helical fibers in the shell of a pteropod Cavolinia globulosa are shown to consist of single-crystalline rod-like building blocks ∼1 μm long and ∼100−200 nm wide. Although the building blocks of the orthorhombic crystal share similar c-axis orientations along the surface normal, their a and b directions rotate in a stepwise fashion. The c...

We introduce high-resolution synchrotron radiation X-ray tomography for nondestructive, three-dimensional reconstruction of the jaw apparatus preserved within the body chamber of the Late Cretaceous phylloceratid ammonoid, Phyllopachyceras ezoensis, for the first time. Analysis of the X-ray images using linear absorption coefficient estimation reve...

This study is the first to report a trend of predation intensity on scaphitid ammonoids from the Turonian to the Maastrichtian (Late Cretaceous) on the basis of analysis of ventral shell breakage in large samples from the US Western Interior Province. Analysis of 835 adult specimens revealed ventral shell breakage in 50 specimens. In most of the da...

The shell microstructure of 30 species belonging to 14 genera and nine families of protobranchs were newly described using scanning electron microscopy. As a result, 13 microstructures were recognized. The shell microstructural composition of protobranchia is conservative at a superfamily level among the Recent species, whereas this trend is not ne...

The morphology of gastropod shells provides a record of the growth rate at the aperture of the shell, and molecular biological studies have shown that the growth rate gradient along the aperture of a gastropod shell can be closely related to gene expression at the aperture. Here, we develop a novel method for deriving microscopic growth rates from...

The siphuncle is a long and narrow segmented soft tissue that occurs in four extant cephalopods with a phragmocone. It contains blood vessels, connective tissue and surrounding epithelium. In ammonoids, this organ was rarely replaced by phosphate minerals.We report here fossilized siphuncular remains from specimens of four ammonoid species. In thes...

We experimentally examined the growth, microstructure, and chemistry of shells of the bloody clam, Scapharca broughtonii (Mollusca: Bivalvia), reared at five temperatures (13, 17, 21, 25, and 29°C) with a constant pCO2 condition (∼450 ppm). In this species, the exterior side of the shell is characterized by a composite prismatic structure, on the i...

During the Last Glacial Maximum (LGM), ice volume reached a relative maximum and global temperature was lower than today. Understanding continental ice volume change requires accurate reconstruction of relative sea level, but tectonic uplift and isostatic adjustment effects complicate many records. Using marine sediment cores from the Bonaparte Gul...

{110} twin density in aragonites constituting various microstructures of molluscan shells has been characterized using X-ray diffraction (XRD) and transmission electron microscopy (TEM), to find the factors that determine the density in the shells. Several aragonite crystals of geological origin were also investigated for comparison. The twin densi...

Because marine benthic animals usually form metapopulations via larval dispersal, a firm grasp of life-history traits is essential to understand the larval dispersal processes and population dynamics of marine benthic communities. Deep-sea hydrothermal vents are ephemeral environments, but they support benthic communities of high biomass. Lepetodri...

吉良哲明氏は1930年代から1960年代にかけて活躍し，日本の貝類学の一時代を築いた功労者の一人である。特に「原色日本貝類図鑑」(吉良，1954, 1959)は日本の貝類界に多大な影響を及ぼした。従って，吉良氏の標本を見直すことは，かつての貝類の分類学の状況を把握する上で意義がある。特に，吉良氏はアオガイ属の3種(クモリアオガイ，ホソスジアオガイ，カスリアオガイ)を記載しており，日本のカサガイ類を研究する上では理解しておくべき重要人物の一人である。吉良氏の標本については，竹之内孝一氏のご尽力によりカタログ化されている(竹之内，2001，2007)。このカタログと標本を照合しながら吉良氏のカサガイ類の同定を確かめた。 本報告では，著者らの同定に関する見解を述べる。標本番号は竹之内氏のカタログに...

In this study, seasonally controlled changes in shell microstructures in Scapharca broughtonii (S. broughtonii, Mollusca: Bivalvia) were demonstrated. We observed shell microstructures and analyzed stable oxygen isotope ratios to reveal the factors controlling cyclical microstructural changes in S. broughtonii. The specimens examined were collected...

The pearl oyster Pinctada fucata has great potential as a model system for lophotrochozoan developmental biology research. Pinctada fucata is an important commercial resource, and a significant body of primary research on this species has emphasized its basic aquaculture biology such as larval biology and growth, aquaculture, pearl formation and qu...

A new species, Solemya (Solemya) flava, is described from a hydrothermal vent field located in the Iheya Ridge in the mid Okinawa Trough, Japan. The small-sized new species is characterized by (1) a branched internal ligament attached to the chondrophore, (2) a bright yellowish brown periostracum, and (3) relatively short shell length relative to h...

The shells of a broad range of land snails were digitally imaged in the near-ultraviolet (NUV), visible and near infrared (NIR). NIR images were recorded in both incident and transmitted illumination. In most cases, shell and periostracal pigmentation observed in the visible range is completely translucent in the NIR, while its contrast is enhanced...

Shell microstructures of five solemyid species from Japan were characterized by scanning electron microscopy. All five species examined had outer and inner shell layers, and were categorized into four groups according to the shell microstructure composition. Group 1 consist of Solemya (Petrasma) pervernicosa and Solemya (Solemya) tagiri. The outer...

In this study, seasonally controlled changes in shell microstructures in Scapharca broughtonii (S. broughtonii, Mollusca: Bivalvia) were demonstrated. We observed shell microstructures and analyzed stable oxygen isotope ratios to reveal the factors controlling cyclical microstructural changes in S. broughtonii. The specimens examined were collected...

The trace fossil Macaronichnus segregatis is an intrastratal trail occurring in shallow marine deposits. Previous studies have shown that this trace fossil can be used as a powerful indicator of ancient sea level, shoreline orientation, beach morphodynamics, and paleoceanographic conditions. Here we describe another type of Macaronichnus, an incipi...

Increases of low-latitude species in various sea areas and poleward shifts of ranges of many species have been reported and linked to warming environments. To examine the generality of these trends for mollusks, we conducted 7 quadrat surveys during 1978–2006 on Pacific rocky shores in Japan (26.6–45.0°N). Results showed that the dominance of south...

With the advent of molecular phylogenetics, the systematics and taxonomy of Patellogastropoda have been greatly improved. Eight families and 36 genera are currently recognized in the order. We review recent published papers that have used molecular data, discuss the resulting advances in systematics and evolution of Patellogastropoda and suggest di...

Cellana nigrolineata is amongst the most common and largest patellogastropod limpets in Japan, and has two color morphs. Analyses of anatomical and morphological characters, shell structure, and mitochondrial COI data (658bp) of these color morphs suggested that they represent intraspecific genetic variation. Molecular analysis demonstrated that th...

Since the first discovery of hydrothermal vents at the Galapagos Spreading Center in 1977, gastropods have gained considerable attention as a major constituent of the chemosynthesis-based biological communities, especially the colonies of large species like Alviniconcha, Ifremeria and Lepetodrilus, or morphologically strange ones like the scaly-foo...

In this study, molluscan shells housed at the University Museum, the University of Tokyo, provided a new set of region-specific correction values (ΔR) for the western Pacific, in particular for the central part of the main islands in the Japanese Archipelago and the southwest islands of Japan. The values of 40 total samples were calculated from 11...

Despite extreme differences between some shallow and deep-sea habitats, the developmental modes and larval forms of deep-sea animals are typically similar to those of their shallow-water relatives. Here we report one of the first documented exceptions to this general rule. The hydrothermal vent snail Ifremeria nautilei displays two novel life-histo...

The microstructure and its crystallographic aspect of the shell of a limpet, Lottiakogamogai, have been investigated, as the first step to clarify the mechanism of shell formation in limpet. The shell consists of five distinct layers stacked along the shell thickness direction. Transmission electron microscopy (TEM) with the focused ion beam (FIB)...

Despite extreme differences between some shallow and deep-sea habitats, the developmental modes and larval forms of deep-sea animals are typically similar to those of their shallow-water relatives. Here we report one of the first documented exceptions to this general rule. The hydrothermal vent snail Ifremeria nautilei displays two novel life-histo...

The anatomy of Nautilus pompilius was reinvestigated on the basis of material from the Philippines to evaluate the “primitiveness” of the living fossil cephalopod. All organ systems were dissected at the gross level, photographed, and described. The results of dissection were compared with the knowledge of other living cephalopods (Coleoidea) and n...

Anatoma fujikurai sp. nov. is described from the hydrothermal-vent environment at Myojin Knoll, southern Japan. The shell of the species is characterized by the predominant axial sculpture on the shoulder and base and by the undulating selenizone. The animal lacks eyes and shows a radular structure not seen in any other . anatomid species examined...