Identify that alga:
Web-based key to genera - 4
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unbranched cyanobacteria (search5) |
branched cyanobacteria (search6) |
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attached, flat plate (search13) |
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Colonies and coenobia : Cyanobacteria (search21) |
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Unicells (under development) |
non-flagellate cells without case (under development) |
in silica case = diatoms (under development) |
flagellate cells (under development) |
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no chloroplast: |
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Unbranched, uniseriate filaments: | Click on the thumbnail for a larger image | |||
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(a) has pyrenoids: (b) no pyrenoids : Pyrenoids are round organelles, usually visible, but more easily seen using Lugol's Iodine: they stain black because they store starch |
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Spirogyra: one of the most readily recognisable filamentous algae, also called "Pond-silk" from its very smooth feel |
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Sirogoniumsuperficially very similar to Spirogyra |
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Mougeotia |
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Mougeotia is the commonest genus answering to this description, but other similar ones exist, which can only be distinguished if zygospores (the product of conjugation) are found. These are:
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Zygnemopsis |
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Mougeotiopsis |
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(a) 2 chloroplasts. Filament has a smooth outline, similar to Mougeotia or Spirogyra; cells long-cylindric. |
Zygnema |
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(b) 1 chloroplast (in most cells - 2 before cell division). Cells are square-cylindric, wall may be thickened and look like Microspora |
Zygogonium |
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(c) 2 chloroplasts, but each cell consists of 2 semicells (is a Desmid). Filament is enclosed in a wide mucilage sheath (shown up with Indian Ink in the accompanying illustration). | Hyalotheca |
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partially or fully encircling the cell; cell wall clearly evident, no sheath. | Ulothrix |
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partially or fully encircling the cell, with 1 or more pyrenoids; cell wall indistinct, filament in an even-textured mucilage sheath. | Geminella |
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usually in middle of cell, but may be indistinct: cells in pairs or spaced out in a lamellate mucilage sheath | Binuclearia |
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band or girdle-shaped, cells in a mucilage sheath similar to Geminella, but no pyrenoid | Gloeotila (no illustration available) | |||
several per cell, band or ring-shaped, cell elongated, contents divided up by clear areas, multinucleate | Sphaeroplea (no illustration available) | |||
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Chloroplast a parietal disc or plate, not completely filling the cell's circumference |
Hormidium (Klebsormidium) |
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Similar
genera: Stichococcus has very short filaments which readily break up, cell diameter from about 1-4µm. Uronema has pointed terminal cells |
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Numerous disc-shaped chloroplasts, wall made of H-pieces | Tribonema |
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Cells barrel-shaped, walls made up of H-pieces, visible at ends of filaments or where they overlap at the middle of the cell | Microspora:Compare with Tribonema, which has elongated, barrel-shaped cells and wall made of H-pieces, but numerous disc-shaped chloroplasts |
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Filament irregular in thickness, cells tapering or bulbous, with rings towards one end of a cell | Oedogonium |
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Filament composed of longer cells than Microspora, similar to an unbranched Cladophora (see amongst branched filaments), but cells not as long; may show "knee-bends" like Klebsormidium, and occasionally rhizoid-like short branches (like Mougeotia) | Rhizoclonium | |||
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This is a frequent finding and causes identification problems | Sometimes it is had to be sure even if there is a chloroplast or not, particularly with preserved or old material: the section below attempts to deal with some of these difficult cases | |||
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Chloroplast present: filament composed of dumbell-shaped cells (or otherwise composed of semicells) linked together, possibly in a mucilage sheath: one of several filamentous Desmid genera |
Filamentous desmids: many look like Cosmarium cells linked end-to-end
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Desmidium: cell width exceeds height, with open median incision. End view is triangular so when seen side-on in a filament some cells show one corner projecting outwards: the cells are linked at a slight angle to each other so these projections form a band which twists round the filament. |
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Hyalotheca: fairly quadrate cells, some with a slight median incision. Stellate chloroplast, mucilage sheath |
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Onychonema: semicells fairly rounded, with 2 long processes at each end which link the cells together, mucilage sheath | ||||
Sphaerozosma: cells with an open or closed median incision, linked by a single process at each end |
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Spondylosium : semicells with open or closed median incision, linked at apices without granules; with sheath. Semicells often different sizes. |
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Teilingia: median incision is open. Cells linked by small granules at apices | ||||
cells in a thick walled filament | (a) wall
an even texture (b) wall appears composed of plates or scales (c) wall lamellate |
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(a)
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Wall an even texture
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Often it is hard to tell whether the wall shows traces of structure or not, as in this illustration. The chloroplast here may be stellate, in which case this is Zygogonium |
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(b)
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Wall composed of plates or scales | probably Microspora: the H-pieces which compose the wall can become thickened and partially detached - more than shown here. Note the chloroplast ought to be a net but is contracted to one end of the cell. Another possibility is: |
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Klebsormidium (crenulatum). | ||||
(c)
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Wall lamellate: | |||
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striations between cells, which may be arranged in pairs |
Binuclearia: related to Ulothrix (see the chloroplast) |
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Wall lamellate,or may be plain, cells long-cylindric, chloroplast may look similar to Mougeotia but indistinct; may show distinctive swollen oospores |
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John Kinross