Home / Charophyceae / Filaments / Desmids / Spondylosium
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Name derivation:
Classification:
Spondylosium Brébisson ex Kützing 1859; 18 of 46 species descriptions are currently accepted taxonomically (Guiry and Guiry 2014). Order Desmidiales; Family Desmidiaceae
Morphology:
Filamentous placoderm desmid with deep isthmus constriction and one chloroplast per cell.
Similar genera:
Diversity within the Genus:
Careful assessment of the genera within the Desmidiaceae class with molecular tools confirmed the polyphyletic nature of almost all traditionally classified genera. It was determined that species of most genera were organized incorrectly into clades, including genera with morphologically uniform species like Spondylosium. Two large clades contained most of the long-branch sequence, and under subclades, the sister groups of Spondylosium pulchellum with Cosmarium regnelli. The other large clade contained another Spondylosium species, S. tetragonum, displaying the genetic diversity within the genus. The two Spondylosium species assigned to the clade “omniradiate” share a filamentous organizational level, but are otherwise not closely related (Gontcharova and Melkonian 2011). This genetic diversity suggests the ability of single genera with morphologically similar species to display more complex genetic diversity through taxonomy.
Cell Jacket Size:
Examining cells overlaid with a polysaccharide cell jacket, Spondylosium panduriforme capsules were taken as essential parts for the cell based on selective permeability. When examined under high magnification, the height of the gelatinous polysaccharide capsule of this freshwater green alga was 130 nm. The capsule material is smooth and continuous, uniformly surrounding the individual cells. This compares to Bacteriastrum diatoms whose cell jacket extends up to 35 µm from the cell center with a directly measured height in a dry state of only 20–30 nm (Bosak et al. 2012).
Cell Capsule Composition and Function:
The accumulation of extracellular polysaccharides is common among the Desmidiales. The filamentous Spondylosium panduriforme has an essential capsule, as described above, composed of polysaccharides in a delicate fibrillar structure. It functions as a selectivity permeable membrane due to polar interactions with the environment. AFM images presented a cell diameter of 23.1 μm and a capsule height of 0.13 μm, while optical microscopy showed a cell diameter of 23.7 ± 1.2 μm and capsule thickness 31.4 ± 1.2 μm (Freire-Nordi et al. 2005). This ratio demonstrated the specie’s dependency on the cell capsule as a selective and functional barrier.
Habitat:
Freshwater in somewhat acidic oligotrophic lakes.
References:
Bosak S., G. Pletikapić, A. Hozić, V. Svetličić and D. Sarno 2012. A Novel Type of Colony Formation in Marine Planktonic Diatoms Revealed by Atomic Force Microscopy. PLoS ONE 7(9): e44851. Freire-Nordi C. S., C. Taciro, R. Bernardes-Filho, N. A. Parizotto, A. A. H. Vieira and O. R. Nascimento 2005. AFM Imaging of Encapsulated Spondylosium panduriforme Alga. Microsc Microanal 11:40-43. Gontcharova, A.A., and M. Melkonian 2011. A Study of Conflict between Molecular Phylogeny and Taxonomy in the Desmidiaceae (Streptophyta, Viridiplantae): Analyses of 291 rbcL Sequences. Protist 162:253-267. Guiry, M.D. and G.M. Guiry 2014. AlgaeBase. World-wide electronic publication, National University of Ireland, Galway. http://www.algaebase.org; searched on 14 April 2014.