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Siliceous planktonic species of the phyla Retaria and Cercozoa were investigated from the surface to a 200 m depth around the eastern Indian Ocean (80.00°–96.10° E, 10.08° N–6.00° S) during a 2-month cruise (10 April–13 May 2014). These species are commonly referred to as Radiolarians and are found in all of the world’s oceans; however, this is a detailed investigation of the species’ diversity in the eastern Indian Ocean. Samples were collected from the eastern Indian Ocean using a plankton towing net during a vertical haul from 44 sampling stations, which resulted in 168 taxa, including 60 species that were newly recorded in the study area. The main purpose of this work was to identify members of the phyla Retaria and Cercozoa and their distribution in the eastern Indian Ocean. The species’ morphology, identification, notes, and new geographical records are briefly described.

Collodaria (Retaria) are important contributors to planktonic communities and biogeochemical processes (e.g., the biologic pump) in oligotrophic oceans. Similarly to corals, Collodaria live in symbiosis with dinoflagellate algae, a relationship that is thought to explain partly their ecological success. In the context of global change, the robustness of the symbiotic interaction, and potential subsequent bleaching events are of primary interest for oceanic ecosystems functioning. In the present study, we compared the ultrastructure, morphology, symbiont density, photosynthetic capacities and respiration rates of colonial Collodaria exposed to a range of temperatures corresponding to natural conditions (21°C), moderate (25°C), and high (28°C) thermal stress. We showed that symbiont density immediately decreased when temperature rose to 25°C, while the overall Collodaria holobiont metabolic activity increased. When temperature reached 28°C, the holobiont respiration nearly stopped and the host morphological structure was largely damaged, as if the host tolerance threshold has been crossed. Over the course of the experiment, the photosynthetic capacities of remaining algal symbionts were stable, chloroplasts being the last degraded organelles in the microalgae. These results contribute to a better characterization and understanding of temperature-induced bleaching processes in planktonic photosymbioses.

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. [ABSTRACT FROM AUTHOR]

In this study, taxonomic criteria were revised for 64 spumellarians/collodarians from the Upper Miocene that were collected at the Ocean Drilling Program Site 1208. The taxonomic approach employed in this study allowed a relatively wide range of intra-species variation to promote palaeoceanographic studies on Upper Miocene fauna in the future. In addition, the nomenclature of species with controversial taxonomies, for which there is significant biostratigraphic interest, was also revised. One such example is Stylatractus universus Hays, which should be renamed as Xiphosphaerantha angelina (Campbell and Clark). In addition, a new species from the Upper to Middle Miocene core sequences was collected at mid-latitudes of the North Pacific Ocean. This species has been named Didymocyrtis noritoshii and can potentially be used as a biostratigraphic and environmental index in core sequences from the Upper Miocene. Dans cette étude, les critères taxonomiques de 64 spumellaires et collodaires du Miocène supérieur, collectés sur le site de l'Ocean Drilling Program 1208 sont révisés. Mon approche taxonomique utilisée dans le cadre de cette étude fut libérale, permettant une certaine marge de variations intra-espèces dans le but de promouvoir à l'avenir les études paléocéanographiques en se basant sur la faune radiolaire du Miocène supérieur. En permettant ainsi une plus large variation morphologique au sein d'une espèce, les taxonomies sont plus simples que si on applique une variation morphologique avec des critères assez stricts pour séparer les espèces. En outre, la nomenclature des espèces aux taxonomies controversées parmi lesquelles y figure une espèce à certain intérêt biostratigraphique a également été révisée. C'est le cas de Stylatractus universus Hays, que j'ai renommé Xiphosphaerantha angelina (Campbell et Clark). Enfin, une nouvelle espèce a pu être décrite dans les séquences sédimentaires datant du Miocène supérieur. Cette espèce, qui a été qui fut nommée Didymocyrtis noritoshii , pourrait potentiellement être utilisée comme indicateur biostratigraphique et environnemental dans l'océan Pacifique du nord. [ABSTRACT FROM AUTHOR]

Simple Summary: Phylum Retaria and Phylum Cercozoa consists of the siliceous planktonic organisms, commonly referred to as Radiolarians, were investigated from 200 m depth to the surface in the eastern Indian Ocean (80.00°–96.10° E, 10.08° N–6.00° S) during a 2 months cruise (10 April–13 May 2014). Samples collected from 44 locations were analyzed by using both light and electron microscopy. Out of 168 taxa, 60 newly recorded species from the groups i.e., Acantharia, Collodaria, Pheodaria, Taxopodida and Polycystinea were recorded for the first time. Siliceous planktonic species of the phyla Retaria and Cercozoa were investigated from the surface to a 200 m depth around the eastern Indian Ocean (80.00°–96.10° E, 10.08° N–6.00° S) during a 2-month cruise (10 April–13 May 2014). These species are commonly referred to as Radiolarians and are found in all of the world's oceans; however, this is a detailed investigation of the species' diversity in the eastern Indian Ocean. Samples were collected from the eastern Indian Ocean using a plankton towing net during a vertical haul from 44 sampling stations, which resulted in 168 taxa, including 60 species that were newly recorded in the study area. The main purpose of this work was to identify members of the phyla Retaria and Cercozoa and their distribution in the eastern Indian Ocean. The species' morphology, identification, notes, and new geographical records are briefly described. [ABSTRACT FROM AUTHOR]

The plankton radiolarian community was investigated in the spring season during the two-month cruise 'Shiyan1' (10 April–13 May 2014) in the Eastern Indian Ocean. This is the first comprehensive plankton tow study to be carried out from 44 sampling stations across the entire area (80.00°–96.10° E, 10.08° N–6.00° S) of the Eastern Indian Ocean. The plankton tow samples were collected from a vertical haul from a depth 200 m to the surface. During the cruise, conductivity–temperature–depth (CTD) measurements were taken of temperature, salinity and chlorophyll a from the surface to 200 m depth. Shannon–Wiener's diversity index (H') and the dominance index (Y) were used to analyze community structure. There was a total of 168 plankton species, composed of Acantharia, Phaeodaria, Polycystina, Collodaria and Taxopodida (monospecific—Sticholonche zanclea, Hertwig is the only recognized species). Hence, it included both celestine-based and siliceous organisms, which are also described here for the first time from this region. Total radiolarians ranged from 5 to 5500 ind/m−3, dominated by co-occurrences of Sphaerozoum punctatum and Stichonche zanclea species at the south-equator zone (SEQ)-transect 80° E and equator zone (EQ)-transect Lati-0. The possible environmental variables were tested through RDA analysis; although no result was obtained for the full species dataset, the samples from the equatorial transect related strongly to mixed-layer chlorophyll a concentration and those of a north–south transect to surface silicate concentrations or mixed-layer nitrate were significantly correlated (p < 0.01) to the radiolarian community. Our results indicate that the silicate and chlorophyll-a concentrations are the two major factors affecting the radiolarian distribution along two of the investigated transects (southern equator and equator) in the study area. [ABSTRACT FROM AUTHOR]