Ultrastructural morphology of the reproductive swarmers of Sphaerozoum punctatum (Huxley) from the East China Sea.
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 8-10 μm 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.
Department of Astronomy and Earth Sciences, Tokyo Gakugei University, Koganei, Tokyo 184-8501, Japan. Electronic address: tyuasa@u-gakugei.ac.jp.
Tomoko
T
Yuasa
Department of Astronomy and Earth Sciences, Tokyo Gakugei University, Koganei, Tokyo 184-8501, Japan.
Osamu
O
Takahashi
D002681:China; D016054:DNA, Protozoan / Q000235:genetics; D004275:DNA, Ribosomal / Q000235:genetics; D002479:Inclusion Bodies / Q000737:chemistry; D008855:Microscopy, Electron, Scanning; D008969:Molecular Sequence Data; D009792:Oceans and Seas; D010802:Phylogeny; D056901:Rhizaria / Q000737:chemistry / Q000145:classification / Q000235:genetics / Q000648:ultrastructure*; D012623:Seawater / Q000469:parasitology; D013052:Spectrometry, X-Ray Emission
D016054:DNA, Protozoan; D004275:DNA, Ribosomal
Colonial radiolaria; Polycystinea; Reproductive swarmer; SSU rDNA; SrSO(4); Ultrastructure