Search

We observed reproductive swarmer cells of the nassellarian and spumellarian polycystine radiolarians Didymocyrtis ceratospyris, Pterocanium praetextum , Tetrapyle sp., and Triastrum aurivillii using light, scanning and transmission electron microscopy. The swarmer cells had subspherical to ovoid or spindle shapes with two unequal flagella tapered to whip-like ends. The cell size was approximately 2.5–5.5 μm long and 1.6–2.2 μm wide, which is significantly smaller than that of the collodarian (colonial or naked) polycystine radiolarians. Transmission electron microscopy revealed that the swarmer cells possessed a nucleus, mitochondria with tubular cristae, Golgi body, and small lipid droplets in the cytoplasm; they also had a large vacuole in which a single crystalline inclusion (approx. 1.0–1.5 μm) that was probably celestite (SrSO 4 ) was enclosed. The swarmer cells were released directly from the parent cells. At that time, morphological change such as encystment was not observed in the parent cells, and the axopodia remained extended in a period of swarmer reproduction for floating existence. This may have prevented the polycystine swarmers from rapidly sinking down to great depths. Thus, we concluded that the polycystine radiolarians release the swarmer cells into the photic layer in the same way as the symbiotic acantharians. [ABSTRACT FROM AUTHOR]

Abstract: Reproductive swarmers of the polycystine radiolarian Sphaerozoum punctatum (Huxley) collected from the East China Sea were examined using light, scanning and transmission electron microscopy. The swarmer cells were about 8–10μm in length with a pear-like shape and a conical end with two flagella. A nucleus, mitochondria, Golgi body, lipid droplets and, characteristically, a single, large, vacuole-bound SrSO4 crystal were present in the cytoplasm. Centering on the crystal inclusion, swarmers swam in a rapid rotational movement both clockwise and anticlockwise. Small subunit (SSU) rDNA sequences obtained for the reproductive swarmer cells from S. punctatum show a monophyletic group together with colonial spumellarians and grouped with S. punctatum from Bermuda in the clade. The morphological features and molecular phylogeny of the reproductive swarmers of S. punctatum show evidence of ancestral traits of radiolarians; acantharians and polycystines have a common ancestry. In addition, SrSO4 inclusion of the swarmer cell may be a form of ballast deposited by the swarmer to allow proper positioning in the water column. We hypothesize that radiolarian-affiliated sequences from SSU rDNA clone libraries of marine picoeukaryotes may be derived from the picoplanktonic cells of radiolarians; i.e., small flagellated life stages such as reproductive swarmers or gametes. [Copyright &y& Elsevier]

Abstract: Polycystines (spumellarians, nassellarians, and collodarians), phaeodarians, and acantharians are marine planktonic protists that have been conventionally and collectively called “radiolaria”. Recent molecular phylogenetic studies revealed radiolarian polyphyly with phaeodarians being a separate offshoot. Collodarians and nassellarians are also shown to form a monophyletic group, but other aspects of radiolarian phylogeny, such as interrelations among polycystines and acantharians, remained uncertain. Here, we present molecular phylogenetic analyses including new ribosomal RNA sequences from ten spumellarians and nine nassellarians, based on Bayesian and maximum-likelihood methods. Results indicate that the Polycystinea is a paraphyletic group, with Bayesian analysis suggesting that spumellarians form a clade with acantharians. The heliozoan-like protist Sticholonche appears as a sister to the spumellarian clade. The nassellarian Eucyrtidium is located outside the clade including the other nassellarians and collodarians. The mineralogy of the test of extant radiolarians and the tree topology obtained in this work suggest that acantharians and spumellarians evolved from an ancestor with a siliceous skeleton. Collodarians and nassellarians form a well-supported clade and one might infer from the fossil record that they may have diverged between the Jurassic and the Eocene. [Copyright &y& Elsevier]

Abstract: Acantharea, Polycystinea, and Phaeodarea have members that are widely distributed in the marine plankton. Many biologists use the conventional term “Radiolaria” to include these three classes. However, on the basis of an 18S rDNA study, Polet et al. (2004, Protist 155, 53–63) recently suggested that the Phaeodarea should be moved into the Phylum Cercozoa. In the present paper, the phylogenetic relationships of the Acantharea and the Polycystinea, especially the phylogenetic positions of Nassellarida and Spumellarida, were inferred from 18S rDNA sequences including those we have determined from the Family Spongodiscidae (Class Polycystinea, Order Spumellarida) and the Family Pterocorythidae (Class Polycystinea, Order Nassellarida). Among major eukaryotic lineages, the Polycystinea were shown to constitute a paraphyletic group: in the phylogenetic trees for the relationships among polycystines, the collosphaerid, sphaerozoid, and thalassicollid spumellarians and the pterocorycid nassellarians constantly formed a monophyletic group, from which the spongodiscid spumellarians were excluded. This conclusion is not consistent with the current taxonomy of the “Radiolaria,” and leads us to consider that the collosphaerid, sphaerozoid, and thalassicollid spumellarians and the pterocorycid nassellarians may have evolved from an ancestor with triradiate branched spicules. [Copyright &y& Elsevier]

Copyright of Revue de Micropaleontologie is the property of Elsevier B.V. and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

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]