The essentials of the taxonomy and cytology of Radiolaria at the order level are summarized from approximately 110 papers. Living Radiolaria comprise representatives of the following orders: Acantharia, Collodaria, Spumellaria, cyrtid Nassellaria, spyrid Nassellaria and Taxopodia (=Sticholonche). This analysis is based on the most recent molecular biological and fossil data. Phaeodaria, which used to belong to the Radiolaria, belong to the Cercozoa now. Heliozoa are closer to the Cercozoa than to the Alveolata or Radiolaria. A molecular phylogenetic analysis indicates that Polycystina (including Collodaria, Spumellaria and Nassellaria) should not be treated as a monophyletic group. “Polycystine” Radiolaria are characterized by the presence of axopodia, a capsular wall, and a fusule. The endoplasm consists of the Golgi bodies, mitochondria, and other organelles, whereas the ectoplasm is an alveolated reticulum with food, digestive, and perialgal vacuoles, suggesting zonal specialization. The Acantharia are characterized by the presence of a periplasmic cortex with myoneme, acting as a motile contractile plasmalemma, rather than a capsular wall. Taxopodia have thick axopodia and a thick nuclear wall instead of a capsular wall. Characteristic protoplasmic structures such as an intracapsular axopodial system and nucleus are found in “polycystine” Radiolaria, but these structures do not seem to reflect phylogenetic relationships.
Diel vertical migration and cellular division processes of Akashiwo sanguinea were investigated in the Ariake Sea in August 2009. The investigation was carried out in the inner part of the Sea for 24 h from 8:00 on 14 August. Water samples were collected every 2 hours, and the temperature, salinity, and chlorophyll fluorescence were monitored hourly. To calculate the in situ growth rate, the duration of the cell division was investigated using incubation experiments in a laboratory. In the Ariake Sea, cells of A. sanguinea were abundant in the subsurface layer in the daytime and at a depth of 4 or 5 m at night. In contrast, cells were mostly absent in the deeper layer in the daytime and in the subsurface layer at night. Downward migration seemed to start at 14:00, indicating that dusk is not the cue for migration. A dense patch was formed at a depth of 5 m from 20:00 to 4:00. The highest frequency of dividing cells was recorded at dusk (18:00) in the Ariake Sea and at light-dark transition (circadian time 14) in the laboratory. The estimated duration of cell division was 1.29 h, and the estimated in situ growth rate was 0.45 d−1. The present study demonstrated that cells of A. sanguinea actively divided in the deeper layer (3.5 to 5 m) from 18:00. To predict red tide occurrence by vertically migrating species, the migration pattern and the growth rate in the natural environment should be further clarified for each species.
A new species of calycophoran siphonophore, Sphaeronectes pagesi sp. nov., is described from material collected in Sagami Bay, Japan. The taxonomic affinities of the other Sphaeronectes species known from Japanese waters are discussed. For S. fragilis, which is reported for the first time from the North Pacific, and S. koellikeri new photographs of the living animals and line drawings are provided.
We determined the nucleotide sequences of the 3′ region (~400 base pairs) of the mitochondrial control region for 97 individuals of the deep-sea demersal fish species Bothrocara hollandi, which were collected at five sites in the northwestern Pacific off Tohoku District, the northeastern part of the Japanese mainland. Phylogenetic analysis based on the sequences showed that these fish form a monophyletic group with individuals of the Okhotsk Sea, which have completely deviated from those fish of the Japan Sea. Furthermore, genetic diversity of fish in the northwestern Pacific was higher than that in the Okhotsk Sea. The population of the northwestern Pacific was shown to have experienced a recent population expansion. Nine of 97 individuals had only one non-coding unit, and the remaining individuals had two units between mitochondrial genes for tRNAThr and tRNAPro; however, neither of these groups of individuals formed a monophyletic group in the Okhotsk Sea or the northwestern Pacific, while monophyly of individuals with more than one unit was shown in the Japan Sea. The differences between the populations of the Japan Sea and neighboring sea areas might be attributed to the occurrence of repeated environmental changes and corresponding population bottleneck events in the Japan Sea.
We conducted field sampling in a subarctic shallow lagoon (Hichirippu Lagoon) in the eastern part of Hokkaido, Japan. We investigated the chemical composition of the water column, sediment, and sinking particles collected by the sediment trap. The standing stock of chlorophyll a (Chl-a) in the water column and surface sediment were 0.4 to 9.3 and 35.9 to 184 mg m−2, respectively. Using stable isotope analysis, the contribution rate of microphytobenthos to the sinking particles was found to range from 63 to 74%. The average Chl-a content in the sinking particles was significantly lower than that of the water column. Our results suggest that the contribution of phytoplankton present in the water column to the Chl-a collected in the traps is likely to be negligible. We assumed that the Chl-a fluxes obtained in this study were microphytobenthic resuspension fluxes. The daily flux of Chl-a accounted for 47.0 to 1,270% of the total standing stock of Chl-a in the water column. The mean relative percentage of daily Chl-a flux divided by the standing stock of Chl-a in the sediment was 6.5%, which indicates that approximately 7% of the microphytobenthos present in the sediment was resuspended, and 93% of the total succeeded at escaping the winnowing action. Although the resuspension phenomenon had little effect on the population of microphytobenthos, the resuspended microphytobenthos had a major impact on the total micro algal biomass in the water column. This is the first direct estimate of microphytobenthic resuspension flux in shallow estuaries.
Two morphological groups of Pseudodiaptomus inopinus were detected in western Japan. One was from the Japan Sea and Tsushima Strait coasts and the other from the Pacific coast including the west and east coasts of Kyushu Island. Differences in females were seen in the posterior processes of the genital operculum, shape of the genital flap, and medial spinules on the first exopodal segment of the fifth leg, and those in males were in the shape of the first exopodal segment of the fifth left leg, and position of the medial process on the third exopodal segment of the fifth right leg. Proportional length of the caudal rami also differed in both sexes. Among these morphologies, the length of the genital operculum process discretely separated each group, but variations in the other morphometric characters were overlapping. Geographic distributions of the two groups were separated with a boundary between two rivers on the northwest coast of Kyushu Island. These results indicate that P. inopinus in Japan is a species complex and specimens from the Japan Sea and Pacific coasts belong to different species.
To investigate the vertical zonation in the copepod community in relation to stratified water-masses, multi-layer sampling at 1–2-m intervals using a submersible pump was conducted on 6 August 2009 in the inner part of Tokyo Bay, central Japan. Acartia sinjiensis showed a peak of the population density in the surface water, which was influenced by river discharge, and Paracalanus parvus s.l. had a peak contrastingly in the mid layer, which was intruded by coastal water from out of the bay through estuary circulation. Calanus sinicus occurred in the coastal water layer with other oceanic copepods. The most dominant species, Oithona davisae showed a remarkable peak in the pycnocline in the 3–6-m layer. Adults of Labidocera rotunda and Pseudodiaptomus marinus and immature copepodids of Hemicylops japonicus accumulated just above the hypoxic bottom-water (DO<1.0 mg L−1). The shallower peak of the bimodally distributed Acartia omorii was very sharp and seemed to be formed by predation by the moon jellyfish Aurelia aurita s.l. on the copepods in the layers above and below the peak. The vertical zonation in the copepod community were reflected by the characteristic environmental conditions in Tokyo Bay in the summer, i.e. estuary circulation, hypoxia in the bottom layer and the distribution of jellyfish.