Misplaced Pages

#518481

16-489: Dictyocha is a genus of silicoflagellates , marine photosynthetic unicellular protists that take the form of either flagellates or axopodial amoebae . Described by Ehrenberg in 1837, Dictyocha contains many important species of the marine phytoplankton , some of them responsible for algal blooms that are toxic to fish . The genus Dictyocha was described in 1837 by Ehrenberg from Algerian fossil material, and its taxonomy has been based exclusively on

32-693: A change of atmospheric conditions. Stagnant water in the presence of decaying matter will typically have an oxygen concentration much less than 100%, which is due to anaerobic bacteria being much less efficient at breaking down organic material. Similarly as in water, oxygen concentration also plays a key role in the breakdown of organic matter in soils. Higher oxygen saturation allows aerobic bacteria to persist, which breaks down decaying organic material in soils much more efficiently than anaerobic bacteria. Thus, soils with high oxygen saturation will have less organic matter per volume than those with low oxygen saturation. Environmental oxygenation can be important to

48-511: A network of hollow rods outside of the cytoplasm . The morphology of the skeleton can vary greatly, from a simple ring, an ellipse or triangle, to a more complex and complete arrangement of rods. For example, in Dictyocha fibula (pictured) the skeleton rods are arranged in a series of peripheral polygons surrounding a central hexagon. These skeletons form a small component of marine sediments , and are well-known microfossils dating as far back as

64-400: Is commonly measured using pulse oximetry . Tissue saturation at peripheral scale can be measured using NIRS . This technique can be applied on both muscle and brain. In medicine , oxygen saturation refers to oxygenation , or when oxygen molecules ( O 2 ) enter the tissues of the body. In this case blood is oxygenated in the lungs , where oxygen molecules travel from the air into

80-573: Is debated. Apart from physical damage to fish, the depletion of dissolved oxygen in water due to their cellular respiration during bloom growth has also caused fish mortality in fisheries and aquaculture. In biological classification , silicoflagellates compose the family Dictyochaceae (in botanical nomenclature ) or Dictyochidae (in zoological nomenclature ), contained within the order Dictyochales or Silicoflagellata . They were previously classified as Chrysophyceae (golden algae). Through morphological and molecular similarities, this group

96-452: The Cenozoic , silicoflagellates show an evolutionary trend towards more complicated apical and basal structures, resulting in a design that resembles a hemisphere . As a consequence, after mitosis , the pair of daughter cell skeletons resembles a near-sphere. Dissolved oxygen Oxygen saturation can be measured regionally and noninvasively. Arterial oxygen saturation (Sa O 2 )

112-608: The Early Cretaceous , around 115 million years ago. However, data on Late Cretaceous and Paleocene silicoflagellate evolution is sparse, and they are best known from the Eocene to Recent era. Silicoflagellate skeletons from the Cretaceous are markedly different from Cenozoic ones: before the Santonian (around 85 million years ago) they presented branched, non-ringed shapes. During

128-475: The early Cretaceous . The silicoflagellates are considered algae due to being photosynthetic . Their chloroplasts are usually present inside the numerous cytoplasmic processes that extend from the central mass of the cytoplasm , where the cell nucleus is located. There is a possibility that silicoflagellate chloroplasts are derived from haptophyte algae through tertiary endosymbiosis. Silicoflagellates are photosynthetic microscopic algae present in

144-951: The flowering plant Distephanus ) and Vicicitus , with 11 recognised living species. Dictyocha was previously the only member of the order, until Vicicitus was created for a species previously assigned to the raphidophyte Chattonella but later proven to be a Dictyochophyceae through phylogenetic analyses . There are also several extinct genera, but their classification is difficult, since skeletons may show diverse forms within each living species. † Cornua † Pseudonaviculopsis † Corbisema archangelskiana group † Corbisema tracantha group † Naviculopsis † Distephanopsis † Caryocha † Paramesocena Octactis Stephanocha Dictyocha † four-sided star-of-David double skeletons † Corbisema apiculata group † Bachmannocena The fossil record of silicoflagellates extends back to early Albian times, in

160-437: The supergroup of eukaryotes known as Stramenopiles . They behave as plankton and are present in oceanic waters . They are well-known from harmful algal blooms that cause high mortality of fish . Additionally, they compose a rich fossil record represented by their silica skeletons. The silicoflagellates are unicellular protists , composed of cells with one emergent flagellum and a siliceous skeleton constructed from

176-494: The sustainability of a particular ecosystem . The US Environmental Protection Agency has published a table of maximum equilibrium dissolved oxygen concentration versus temperature at atmospheric pressure. The optimal levels in an estuary for dissolved oxygen is higher than six ppm. Insufficient oxygen ( environmental hypoxia ), often caused by the decomposition of organic matter and nutrient pollution , may occur in bodies of water such as ponds and rivers , tending to suppress

SECTION 10

#1733093305519

192-407: The blood. Oxygen saturation (( O 2 ) sats) measures the percentage of hemoglobin binding sites in the bloodstream occupied by oxygen. Fish, invertebrates, plants, and aerobic bacteria all require oxygen. In aquatic environments, oxygen saturation is a ratio of the concentration of "dissolved oxygen " (DO, O 2 ), to the maximum amount of oxygen that will dissolve in that water body, at

208-483: The morphology of their siliceous skeletons. Dictyocha was regarded as the sole genus of the entire family Dictyochaceae and order Dictyochales (known as silicoflagellates sensu stricto ) until 2012, when a second genus Vicicitus was described. There are currently four accepted species of Dictyocha : Silicoflagellate The silicoflagellates (order Dictyochales ) are a small group of unicellular photosynthetic protists , or algae , belonging to

224-405: The temperature and pressure which constitute stable equilibrium conditions. Well-aerated water (such as a fast-moving stream) without oxygen producers or consumers is 100% saturated. Stagnant water can become somewhat supersaturated with oxygen (i.e., reach more than 100% saturation) either because of the presence of photosynthetic aquatic oxygen producers or because of a slow equilibration after

240-631: The upper part of the marine water column , as plankton . They are adapted to both warm and cold waters. Similarly to diatoms , silicoflagellates are most productive where high levels of silica and nutrients are present in near-surface waters. They are known to cause harmful algal blooms , or red tides , in many parts of Europe. Blooms of silicoflagellates cause fish mortality because their silica skeletons obstruct and abrade fish gills , leading to asphyxiation and subsequent death. Additionally, some silicoflagellates are thought to produce ichthyotoxins , i.e. substances toxic to fish, although their effect

256-539: Was eventually transferred to the Dictyochophyceae , which contains three additional orders, Pedinellales , Florenciellales and Rhizochromulinales . After decades of phylogenetic analyses , silicoflagellates and the rest of Dictyochophyceae are accepted as a class of the phylum Ochrophyta , within the eukaryotic supergroup Stramenopiles . There are four living genera: Dictyocha , Octactis , Stephanocha (earlier known as Distephanus , homonymous with

#518481