filaments

Description:

Debarya sp. (Chlorophyta, Zygnematales) is a filamentous green algal that invaded Lake Kinneret in 1998. It blooms in the spring of years when Peridinium gatunense fails to bloom.   At the moment, we have never seen conjugation taking place and therefore can not identify it to species level and also are not sure that this is Debarya rather than Mougeotia sp. The genus Debarya is rare worldwide, but was common in geological times as can be found in sediment samples.   Genus description (from AlgaBase): Thalli unbranched, forming extensive skeins of intertwining uniseriate filaments. Cells cylindrical 6-30 µm in diameter, several times as long; cell wall two-layered with inner cellulose, outer mucilage layer; endwalls plane; no flagellated stages. Cells uninucleate; chloroplasts axile; flat ribbonlike or platelike; one or two per cell; pyrenoids in row or scattered. Asexual reproduction by fragmentation, akinetes, parthenospores, and aplanospores. Life cycle haplobiontic, meiosis zygotic. Sexual reproduction by scalriform conjugation; gametes isogamous, fuse within conjugation tube. Zygospores distinctly tricarinate with three keels, or sharp edges.   Filaments usually found as free-floating masses. All species rare, but collected from Eruope, Asia, North America, and New Zealand. Earliest fossil zygospores reported from Permian Period (250 million years b.p.); in contrast to modern distribution, fossil keeled spores quite common in sediments where Zygnemataceae found, especially in cold or cool climates in high-mountain treeless plains (paramos) of Colombian Andes; used as marker for clean, oxygen-rich, shallow stagnant, mesotrophic water in habitats subject to seasonal warming. Originally D. glyptosperma described as a species of Mougeotia; Debarya may be related to latter. Trait of conjugation places in Zygnematales but otherwise phylogenetic position unclear.