Hyella
| Generic name: HYELLA Bornet et Flahault, 1886. J. Bot. 2: 163. | ||||||||||
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| Type species: Hyella caespitosa Bornet et Flahault 1888 |
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| Descriptions: Komárek & Anagnostidis (1998): Thallus highly differentiated, composed of irregular, more or less ramified (rarely simple) pseudofilaments, creeping on calcareous substrates (usually limestone or shells of molluscs, rarely on other stones or on plants), but mainly euendolithic (or endophytic) growing into the substrate (boring types). Pseudofilaments with one or more rows of cells, sometimes in older parts are formed irregular groups of cells, often nematoparenchymatously arranged; pseudofilaments usually laterally (rarely pseudodichotomously) divaricate. Thus, thallus is differentiated into (1) initial, epilithic or superficially endolithic part, from which grow (ii) pseudofilaments into the substrate (sometimes with branching); apical parts of endolithic pseudofilaments (i.e., deepest parts in the substrate) are usually morphologically different from initial pseudofilaments. Mucilaginous sheaths are firm, thick, usually layered, rarely gelatinized and commonly visible also between cells. Cells more or less spherical, subspherical, oval or rounded polygonal, of diverse size, sometimes distinctly elongate, cylindrical, ovoid, at the ends of pseudofilaments oval or club-shaped (rarely hemispherical). Thylakoids irregularly arranged (H. balani, H. caespitosa). Komárek (1992): Pseudofilamentous; thallus composed from filament-like, irregular rows of cells creeping on substrate (usually carbonate rich) or/and boring it. Initial (surface) stages are gathered cell groups enveloped by own, distinct, colourless, firm sheaths (chroococcalean stages). Pseudofilaments grow into the stony substrate from the "basal nematoparenchymatous colony, uniseriate or (rarely) polyseriate, laterally pseudobranched (divaricated) with different frequency, enveloped by thin or thickened, firm or mucilaginous, sometimes layered sheaths, straight or slightly curved, at the ends with distinctly elongated terminal and subterminal cells. |
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| Genotype differences, molecular data: | ||||||||||
| Reproduction strategies, life cycles, cell division: Komárek & Anagnostidis (1998): Cells divide by binary fission, irregularly in various planes, in pseudofilaments crosswise (perpendicularly to the long axis of pseudofilament), before branching also lengthwise or obliquely. Oldest cells near the substrate surface often change into baeocytes, which arise after rapid successive or almost simultaneous repeated cell division (multiple fission). Reproduction by baeocytes, rarely by liberation of solitary small cells (?). Komárek (1992): Cells divide irregularly in different planes, in boring pseudofilaments mainly crosswise. Enlarged cells divide sometimes in nanocytes, usually in the surface parts of thallus. Reproduction by nanocytes and by solitary cells, surrounded by gelatinous envelopes; they divide irregularly and the pseudofilaments differentiate soon from them. |
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| Ultrastructure: | ||||||||||
| Taxonomic position, higher hierarchy: Cyanophyceae, Chroococcales, Hyellaceae, Hyelloideae Notes to taxonomy, misinterpretations: Komárek & Anagnostidis (1998): Two groups of species, differing in the method of thallus differentiation (LeCampion-Alsumard & Golubić 1985) were recognized within the genusHyella. These differences result from the different strategies of cell division and branching patterns, and from the succeeding life cycles. Anagnostidis & Pantazidou (1988) proposed also two subgenera under the provisional names "Megayella" and "Microhyella", based on cell division, branching pattern, mode of reproduction and life cycles. Both models express two patterns of thallus development, characteristic for (i) H. balani or H. fontana (and more or less species 1-8), and (ii) H. caespitosa (and more or less for species 9-12). The third modification is probably represented by endophytic species (H. dilseae, H. endophytica, H. seriata). |
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| Ecology, ecophysiology, ecological significance: Komárek (1992): All species grow in submerse biotopes, on limestone substrates, either in marine (stony and rocky sea littoral, shells,old corral reefs), or in freshwater biotopes (usually in not polluted creeks). Marine species probably with wide distribution in all seas of the tropical and temperate zones. In spite of it, majority of species is little known and needs further studies. Distribution of frehwater species is known a little only. |
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| Physiology and biochemistry: |
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| Distribution, endemism, problematic citations: |
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| Reference strain: |
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| Infrageneric scheme, species concept: |
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| List of species: Hyella arbuscula Al-Thukair 1992 Hyella balani Lehmann 1903 Hyella caespitosa Bornet et Flahault 1888 Hyella conferta At-Thukair et Golubić 1991. Archiv für Hydrobiologie/Algological Studies 64: 174 Hyella dalmatica Ercegović 1932 Hyella dilseae (Feldmann) Komárek et Anagnostidis 1995 Hyella endophytica Börgesen 1903 Hyella fontana Huber et Jadin1892 Hyella gigas Lucas et Golubić 1983 Hyella immanis Al-Thukair et Golubić 1991 Hyella inconstans Al-Thukair et Golubić 1991. Archiv für Hydrobiologie/Algological Studies 64: 182 Hyella jurana Chodat 1898 Hyella kalligrammos Anagnotidis et Pantazidou 1988 Hyella littorinae Setchel et Gardner in Gardner 1918 Hyella maxima (Geilter) Anagnostidis et Pantazidou 1988 Hyella pyxis Lucas et Hoffman 1984 Hyella racemus Al-Thukair et al. 1994 Hyella reptans Al-Thukair et Golubić 1991. Archiv für Hydrobiologie/Algological Studies 64: 171 Hyella salutans Al-Thukair et Golubić 1991. Archiv für Hydrobiologie/Algological Studies 64: 179 Hyella seriata (Hollenberg) Komárek et Anagnostidis 1995 Hyella simplex Chu et Hua 1982 Hyella stella Al-Thukair et Golubić 1991. Archiv für Hydrobiologie/Algological Studies 64: 180 Hyella tenuior Ercegović 1932 Hyella terrestris Chodat 1921 Hyella vacans Gektidis et Golubić 1996 Unclear taxa: |
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Drawings: Komárek 1992
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