Overview

Brief Summary

Taxonomy

Nitzschiatom species are usually identified by the shape and patterns of the silica walls. Strong, short ribs under a keel along the valve (half wall) are a diagnostic character for the genus Nitzschia, of which N. sigmoidea is the type species.The different species of Nitzschia are usually recognised by the shape and size of their valves, the density and orientation of rows of pores across their surface, and the short ribs that span the raphe, which often lies along the ridge of a lateral keel. The raphe is usually formed of a pair of longitudinal slits in the wall through which mucilage can be secreted.Diatom cells are described in two views – valve and girdle view. Cells of N. sigmoidea are more or less sigmoid in girdle view, and linear with wedge-shaped ends in valve view. Cells are about 100-500µm long (0.1-0.5mm), 8-15µm wide in valve view, and about 30µm wide in girdle view. Girdle width varies with the stage of the cell cycle. The raphe keel is slightly off-centre, with irregularly spaced ribs spanning the keel (about 5-7 in 10 µm). Parallel rows of pores cross the valve surface, 23-27 rows in 10µm.The girdle region is formed of several open bands that also contain pores.With electron microscopy more detail of the wall structure is visible.
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Introduction

Nitzschia sigmoidea is a large freshwater diatom (microscopic alga) that can be found growing on the surface of mud in ponds and streams.Large populations of these diatoms can form a golden-brown coating on rocks and sediments, and are often clearly visible on intertidal muds at low tide.Nitzschia sigmoidea is relatively large and distinctive but still less than 0.5mm long . Nitzschia sigmoidea was one of the first diatoms to be described in 1817 (as Bacillaria sigmoidea). Later (1853) William Smith (an early British diatomist) created a new genus (Nitzschia) for this species, naming it after Christian Ludwig Nitzsch, the German zoologist who had first found it in Halle, Germany.
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Comprehensive Description

Biology

Nitzschia sigmoidea there are two chloroplasts - one at each end of the long, s-shaped cells.Like many diatoms, Nitzschia species are able to glide over surfaces by secreting mucilage. Large populations of these diatoms can form a golden-brown coating on rocks and sediments, and are often clearly visible on intertidal muds at low tide.
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Distribution

Distribution and ecology

Nitzschia sigmoidea is a common widespread diatom that often grows on soft sediments in ponds. It has been recorded from Europe, North America and more recently from Japan.Cells of another, much smaller, diatom - Amphora pediculus, are often found sitting on live cells of N. sigmoidea.
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Ecology

Habitat

Depth range based on 163 specimens in 1 taxon.
Water temperature and chemistry ranges based on 2 samples.

Environmental ranges
  Depth range (m): 0 - 20
  Temperature range (°C): 0.329 - 4.181
  Nitrate (umol/L): 0.927 - 2.140
  Salinity (PPS): 26.346 - 34.375
  Oxygen (ml/l): 7.135 - 8.163
  Phosphate (umol/l): 0.064 - 0.366
  Silicate (umol/l): 3.266 - 10.627

Graphical representation

Depth range (m): 0 - 20

Temperature range (°C): 0.329 - 4.181

Nitrate (umol/L): 0.927 - 2.140

Salinity (PPS): 26.346 - 34.375

Oxygen (ml/l): 7.135 - 8.163

Phosphate (umol/l): 0.064 - 0.366

Silicate (umol/l): 3.266 - 10.627
 
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Life History and Behavior

Reproduction

All diatom cells have an older and a younger half-wall, known as the epi- and hypo-theca respectively. When diatom cells divide vegetatively, the two offspring inherit one half-wall but must generate a new half-wall (semi-conservative wall development). Thus the hypotheca of the parent cell becomes the epitheca of one of the offspring (the epitheca of the parent becomes the epitheca of the other offspring).New walls are formed within the protoplast of the offspring, in a special membrane-bound vesicle, the silica deposition vesicle (SDV). When the new half-wall is complete, there is reorganisation of the plasmalemma (cell membrane) and the silicalemma (membrane of the SDV), so that the inner face of the SDV becomes part of the plasmalemma.The close juxtaposition of developing sibling valves means that they sometimes have corresponding humps and depressions, but also that they can become linked together to form colonies by the formation of interlocking spines around their margins. This is particularly found in diatoms that live in the plankton.
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Relevance to Humans and Ecosystems

Benefits

Uses

The fossil remains of diatoms, diatomite or Kieselguhr, have a range of uses, including as a filtration aid, a mild abrasive in toothpaste and metal polish, a mechanical insecticide, an absorbent for liquids, cat litter and as a component of dynamite.Because different species have particular ecological requirements and distributions, diatoms are used in water quality analysis, e.g. Water Framework Directive, and are also useful to forensic scientists.
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