ABSTRACT
The phylogenetic affiliation of Oroscenidae, a family of Radiolaria possessing large siliceous skeletons, was thoroughly revised in this study. Plankton sampling was conducted over seven years in seven sea areas of the Northern Hemisphere. Molecular analyses on the obtained specimens revealed that living oroscenids are phylogenetically different from hitherto-known radiolarian orders. The detailed examinations by Microfocus X-ray Computed Tomography and Scanning Electron Microscopy clarified that oroscenids and the related family (Thalassothamnidae) have unique skeletal characteristics different from other radiolarian orders. Judging from their phylogenetic distinctiveness and the difference in the morphology and ecology, Oroscenidae and Thalassothamnidae should be classified in a single order distinct from other radiolarian orders, and consequently, a new order, Orodaria, is established.
Subject(s)
Rhizaria , Microscopy, Electron, Scanning , PhylogenyABSTRACT
Cross-sections were prepared by ultramicrotome (UM) and focused ion beam (FIB) system in order to examine the skeletal structure of ecologically and geologically important shell-bearing protists: phaeodarians and radiolarians. The elemental composition of the skeleton was clarified by the energy dispersive X-ray spectroscopy, suggesting that the skeletons of both groups are mainly made of amorphous silica (SiO2·nH2O) with other minor elements (Na, Mg, Al, Cl, K, Ca and Fe) and that these two groups have similar elemental composition, compared with other siliceous organisms (diatoms and sponges). However, the structural difference among the two groups was confirmed: phaeodarian skeletons are porous, unlike radiolarians with solid skeletons. It was also revealed that the phaeodarian skeleton contains concentric layered structure with spaces, presumably related to the ontogenetic skeleton formation. The distinction in the skeletal ultrafine structure (porous/solid and non-dense/dense) would reflect the ecological difference among the two groups and could be an effective criterion to determine whether microfossils belong to Radiolaria or Phaeodaria. The UM and FIB combined method presented in this study could be a useful approach to examine the chemical and structural characteristics of unculturable and/or rare microorganisms.
Subject(s)
Silicon Dioxide/chemistry , Cercozoa/ultrastructure , Microscopy, Electron, Transmission , Rhizaria/ultrastructure , Skeleton/ultrastructure , Spectrometry, X-Ray EmissionABSTRACT
A phaeodarian morphotype, characterized by the feet surrounded with forked pedal spines with anchor-like structures, was collected in the subtropical North Pacific. Considering the morphological and phylogenetic uniqueness, this morphotype is described as Gazelletta kashiwaensis sp. nov. The distribution of this new species is possibly affected by the Kuroshio Current. The feeding behavior of living phaeodarians was first filmed: the present new species floated in the water column stretching "protoplasmic webs" and collected diatoms by repeating the expansion and retraction of "pseudopodium-like tentacles".
