Noritoshi Suzuki

Drilling reveals climatic consequences of Tasmanian Gateway Opening

One of the great stories of geoscience is how Gondwana broke up and the other southern continents drifted northward from Antarctica, which led to major changes in global climate. The recent drilling of Ocean Drilling Project (ODP) Leg 189 addressed in detail what happened as Australia drifted away from Antarctica and the Tasmanian Gateway opened. The drifting contributed to the change in global climate, from relatively warm early Cenozoic “greenhouse” conditions to late Cenozoic “icehouse” conditions. It isolated Antarctica from warm gyral surface currents from the north and provided the critical deepwater conduits that eventually led to ocean conveyor circulation between the Atlantic and Pacific Oceans.

Brandtodinium gen. nov. and B. nutricula comb. Nov. (Dinophyceae), a dinoflagellate commonly found in symbiosis with polycystine radiolarians

Symbiotic interactions between pelagic hosts and microalgae have received little attention, although they are widespread in the photic layer of the world ocean, where they play a fundamental role in the ecology of the planktonic ecosystem. Polycystine radiolarians (including the orders Spumellaria, Collodaria and Nassellaria) are planktonic heterotrophic protists that are widely distributed and often abundant in the ocean. Many polycystines host symbiotic microalgae within their cytoplasm, mostly thought to be the dinoflagellate Scrippsiella nutricula, a species originally described by Karl Brandt in the late nineteenth century as Zooxanthella nutricula. The free‐living stage of this dinoflagellate has never been characterized in terms of morphology and thecal plate tabulation. We examined morphological characters and sequenced conservative ribosomal markers of clonal cultures of the free‐living stage of symbiotic dinoflagellates isolated from radiolarian hosts from the three polycystine orders. In addition, we sequenced symbiont genes directly from several polycystine‐symbiont holobiont specimens from different oceanic regions. Thecal plate arrangement of the free‐living stage does not match that of Scrippsiella or related genera, and LSU and SSU rDNA‐based molecular phylogenies place these symbionts in a distinct clade within the Peridiniales. Both phylogenetic analyses and the comparison of morphological features of culture strains with those reported for other closely related species support the erection of a new genus that we name Brandtodinium gen. nov. and the recombination of S. nutricula as B. nutricula comb. nov.

Molecular Phylogeny and Morphological Evolution of the Acantharia (Radiolaria)

Acantharia are ubiquitous and abundant rhizarian protists in the world ocean. The skeleton made of strontium sulphate and the fact that certain harbour microalgal endosymbionts make them key planktonic players for the ecology of marine ecosystems. Based on morphological criteria, the current taxonomy of Acantharia was established by W.T. Schewiakoff in 1926, since when no major revision has been undertaken. Here, we established the first comprehensive molecular phylogeny from single morphologically-identified acantharian cells, isolated from various oceans. Our phylogenetic analyses based on 78 18S rDNA and 107 partial 28S rDNA revealed the existence of 6 main clades, sub-divided into 13 sub-clades. The polyphyletic nature of acantharian families and genera demonstrates the need for revision of the current taxonomy. This molecular phylogeny, which highlights the taxonomic relevance of specific morphological criteria, such as the presence of a shell and the organisation of the central junction, provides a robust phylogenetic framework for future taxonomic emendation. Finally, mapping all the existing environmental sequences available to date from different marine ecosystems onto our reference phylogeny unveiled another 3 clades and improved the understanding of the biogeography and ecology of Acantharia.

PERMIAN RADIOLARIAN FAUNAS FROM CHERT IN THE KHABAROVSK COMPLEX, FAR EAST RUSSIA, AND THE AGE OF EACH LITHOLOGIC UNIT OF THE KHABAROVSK COMPLEX

Abstract The Khabarovsk Complex, a Jurassic accretionary complex distributed in and around the Khabarovsk city area, Far East Russia, comprises mélange and schist facies. From the review of previous studies including Russian papers, the lithology and age of the constituent rocks of the mélange facies can be summarized as follows: Upper Paleozoic basic volcanic rocks, mainly pillow lava, and altered gabbro, Upper Carboniferous to Upper Permian fusulinoidean-bearing limestone associated with tuff, Lower and Middle Jurassic siliceous mudstone, Upper Jurassic tuffaceous mudstone, uppermost Jurassic carbonate concretions embedded in mudstone, and age-unknown sandstone. Newly found sequences of limestone-chert and of basalt-chert in the mélange facies crop out along the Amur River in the Khabarovsk city area. A chert sample of the limestone-chert sequence contains Albaillella aff. asymmetrica and Pseudoalbaillella aff. lomentaria, and a chert sample of the basalt-chert sequence includes Follicucullus monacanthus, Follicucullus porrectus, and Pseudoalbaillella cf. yanaharaensis. The radiolarian assemblages from the limestone-chert and basalt-chert sequences have a maximum age of middle Early Permian and late Middle Permian, respectively, overlapping the time of deposition of the fusulinoidean-bearing limestone. The co-occurrence of chert and limestone indicates that the fusulinoidean-bearing limestone was formed on a basaltic topographic high in a pelagic ocean whereas the radiolarians accumulated in a deeper part. Limestone debris occasionally flowed into the depositional site of the radiolarian chert. Although the Khabarovsk Complex was simply considered as a northern extension of the Mino–Tamba Belt of the Inner Zone of southwest Japan, we propose a new correlation based on the lithologic associations. The mélange facies of the Khabarovsk Complex is correlative with one of the Kasugano, Funabuseyama, Nabi, and Yabuhara Formations in the Mino–Tamba Belt, whereas the schist facies is correlative with the Hikami Formation of the Ultra–Tamba Belt.

ONTOGENETIC GROWTH AND VARIATION IN THE SKELETAL STRUCTURE OF TWO LATE NEOGENE SPHAEROPYLE SPECIES (POLYCYSTINA RADIOLARIANS)

Abstract Two four-shelled species characterized by a pylome-bearing outermost shell—Sphaeropyle robusta and its descendant, Sphaeropyle langii—are selected for morphological study. Both species are morphologically identical to three-shelled Actinomma morphotypes, morphotypes A and B, respectively. Furthermore, the number of pores on half a circumference of the primary cortical shell, the distinguishing feature between Sphaeropyle robusta and Sphaeropyle langii, accounts for the same between Sphaeropyle robusta and morphotype A, and between Sphaeropyle langii and morphotype B. It suggests that the three-shelled morphotypes A and B are juvenile forms of the four-shelled Sphaeropyle robusta and Sphaeropyle langii, respectively. This is strongly supported by the same stratigraphic distributions of each pair. The quantitative analysis of morphological variations in both species also revealed that they have nearly identical morphology, except for the number of pores on half a circumference of the primary cortical shell. In addition, the size range of primary and secondary cortical shells and the range of the number of radial spines increase in Sphaeropyle langii, while the length range of radial spines decrease.

Biology and Ecology of Radiolaria

Radiolaria are unicellular holoplanktonic protozoa with siliceous or strontium sulfate skeletons. Mainly studied by micropaleontologists because of their excellent fossil record, they are also key members of planktonic communities and play important roles in various oceanic ecosystems. This chapter presents an overview of the current knowledge on living Radiolaria (orders Acantharia, Collodaria, Nassellaria, Spumellaria and Taxopodia). Besides general considerations on Radiolaria as a whole, it focuses on the taxonomy, biology, and ecology of each radiolarian order. Finally this chapter provides insights on research perspectives to improve our knowledge of living radiolarians and their ecological role in marine ecosystems.

Middle to Upper Pleistocene Polycystine Radiolarians from Hole 902-C9001C, Northwestern Pacific

A continuous 740-kyr Quaternary sedimentary sequence containing abundant siliceous microfossils was recovered from Hole C9001C during the D/V Chikyu 2006 Mission off the Shimokita Peninsula, Japan. This region is characterized by mixed water reflecting the influences of one warm current (Tsugaru Current), one cold current (the Oyashio Current), and several intermediate and deep water masses. Polycystine radiolarians (a siliceous microfossil group) are useful for reconstructing paleoceanographic changes in this region during the Quaternary because of their ecological properties in these types of deep-sea sediments. This paper illustrates and reviews the taxonomic features of all the polycystine species encountered during this study. A detailed taxonomy is presented because different taxonomic names have been applied, even to the same morphospecies, in many cases. The taxonomic classification of 104 species belonging to three orders (Collodaria, Spumellaria, and Nassellaria), 16 superfamilies, 33 families, and 66 genera was verified by comparison of the holotypes and the relevant name-bearing specimens in accordance with the International Code of Zoological Nomenclature to the extent possible. The taxonomic classification system was updated with reference to both recent morphological taxonomic schemes and molecular phylogenetic analyses. This paper also provides a detailed synonym list of each previously illustrated species from the northwestern Pacific Ocean in order to standardize applicable taxonomic names for the same morphospecies. In addition, a new family (Amphisphaeridae Suzuki fam. nov.) and a new replacement name (Lithelius haeckelispiralis Matsuzaki and Suzuki, nomen nov. for Lithelius spiralis of Haeckel in 1861 [not Ehrenberg in 1840]) are described, and the diagnoses of the genus Tholomura and the family Lychnocaniidae are emended.

The Ehrenberg type species of flat-shaped radiolarian genera (Spongodiscidae and Stylodictyidae, Spumellaria, Polycystina)

Synopsis Original material for almost all of the polycystine radiolarian species described by Christian Gottfried Ehrenberg (∼8o genera, ∼530 species) are housed in the Museum für Naturkunde, Berlin. Eleven type specimens of 10 spongodiscid and stylodictyid radiolarian genera were found in Ehrenbergs original mica strips. These micas are from six different sample locations and range in geological age from (approximately) late Eocene to Holocene. Ten specimens are confirmed as those sketched by Ehrenberg and are designated as lectotypes. Consequently, Dictyocoryne profunda is the senior valid synonym of Euchitonia für cata and Rhopalodictyum abyssorum. The Ehrenberg collection contains several specimens identified as F. concentrica, the type species of the genus Flustrella. After careful examination, the best preserved specimen was defined as the lectotype and, as a result, Flustrella (type species: F. concentrica) is confirmed as a valid name, while Porodiscus (Trematodiscus orbiculatus) and Trematodiscus (T. orbiculatus) are junior synonyms of Flustrella. The type species of Spongodiscus (S. resurgens), Spongaster (S. tetras) and Dictyocoryne (D. profunda) possess concentric internal structures, suggesting close phylogenetic relationships with Flustrella. Lectotypes of Stylodictya (S. gracile), Perichlamydium (Flustrella praetexta), and Stephanastrum (S. rhombus) are designated.

Towards an Integrative Morpho-molecular Classification of the Collodaria (Polycystinea, Radiolaria)

Collodaria are ubiquitous and abundant marine radiolarian (Rhizaria) protists. They occur as either large colonies or solitary specimens, and, unlike most radiolarians, some taxa lack silicified structures. Collodarians are known to play an important role in oceanic food webs as both active predators and hosts of symbiotic microalgae, yet very little is known about their diversity and evolution. Taxonomic delineation of collodarians is challenging and only a few species have been genetically characterized. Here we investigated collodarian diversity using phylogenetic analyses of both nuclear small (18S) and large (28S) subunits of the ribosomal DNA, including 124 new sequences from 75 collodarians sampled worldwide. The resulting molecular phylogeny was compared to morphology-based classification. Our analyses distinguished the monophyletic clade of skeleton-less and spicule-bearing Sphaerozoidae from the sister clades Collosphaeridae (skeleton-bearing) and Collophidiidae (skeleton-less), while the Thalassicollidae was not retrieved as a monophyletic clade. Detailed morphological examination with electron microscopy combined with molecular analyses revealed many discrepancies, such as a mix between solitary and colonial species, co-existence of skeleton-less and skeleton-bearing specimens within the Collosphaeridae, as well as complex intraspecific variability in silicified structures. Such observations challenge a morphology-based classification and highlight the pertinence of an integrative taxonomic approach to study collodarian diversity.

Paleoceanographic affinities of radiolarian faunas in late Aalenian time (Middle Jurassic) recorded in the Jurassic accretionary complex of Japan

Abstract A total of 140 polycystine radiolarians (84 nassellarians and 56 spumellarians; called Mn-03 assemblage herein) were identified from a manganese nodule in mudstone of the chert–clastic sequence distributed in the Jurassic accretionary complex of the Kuzumaki–Kamaishi Belt, Northern Kitakami Mountains, Northeast Japan. The horizon yielding this well-preserved assemblage was correlated to the uppermost part of the radiolarian JR4 Zone (the Upper Aalenian, Middle Jurassic) on the basis of the presence of Tricolocapsa tegiminis , the probable decendant of Laxtorum (?) jurassicum , and the absence of L. (?) jurassicum and Tricolocapsa plicarum . The Mn-03A assemblage is of high diversity but shows nearly half of the diversity of the contemporaneous assemblage which was reported from manganese nodules in another Jurassic accretionary complex of the Mino Belt in Japan. Both assemblages are considered to have been derived from the same province due to faunal similarity. The difference between both assemblages is explained by lower productivity in the depositional region of the Mn-03A assemblage. Comparison of the Mn-03A assemblage to the contemporaneous assemblage indicates that the fauna lived in the equatorial to lower latitudinal zone of the Pacific Superocean in late Aalenian time.