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The genus Cryptomonas is easily recognized by having two flagella, green brownish color, and a swaying behavior. They have relatively simple morphology, and limited diagnostic characters, which present a major difficulty in differentiating between species of the genus. To understand species delineation and phylogenetic relationships among Cryptomonas species, the nuclear-encoded internal transcribed spacer 2 (ITS2), partial large subunit (LSU) and small subunit ribosomal DNA (rDNA), and chloroplast-encoded psbA and LSU rDNA sequences were determined and used for phylogenetic analyses, using Bayesian and maximum likelihood methods. In addition, nuclear-encoded ITS2 sequences were predicted to secondary structures, and were used to determine nine species and four unidentified species from 47 strains. Sequences of helix ?, ??, and ???b in ITS2 secondary structure were very useful for the identification of Cryptomonas species. However, the helix ?V was the most variable region across species in alignment. The phylogenetic tree showed that fourteen species were monophyletic. However, some strains of C. obovata had chloroplasts with pyrenoid while others were without pyrenoid, which used as a key character in few species. Therefore, classification systems depending solely on morphological characters are inadequate, and require the use of molecular data.
Key Words: Cryptomonas; Cryptophyta; morphology; phylogeny; taxonomy
INTRODUCTION
The genus Cryptomonas, which belongs to the class Cryptophyceae, was established by Ehrenberg (1831). It is distributed in freshwater habitats worldwide. Cells can be easily recognized by two unequal biflagella, olive-brownish to olive-greenish in color, large ejectisomes lined in the furrow-gullet system, and a peculiar swaying swimming behavior due to the asymmetric shape, dorsally flattened and ventrally concave in lateral view. Cells have two chloroplasts originated from red algae, which contain the accessory pigment phycoerythrin 566 of phycobiliprotein (Hill and Rowan 1989, Clay et al. 1999, Deane et al. 2002, Hoef-Emden and Melkonian 2003). Cryptomonas species display one or two morphotypes within a clonal culture. In the cryptomorph, the inner periplast component (IPC) is made of hexagonal to polygonal plates, whereas in the camphylomorph the IPC is a sheet-like layer (Faust 1974, Brett and Wetherbee 1986, Hill 1991, Hoef-Emden and Melkonian 2003, Hoef-Emden 2007).
Since Ehrenberg (1831, 1832) described six Cryptomonas species, many additional species were added (Pascher 1913, Schiller 1925, 1929, 1957, Skuja 1939, 1948, 1956, Huber-Pestalozzi 1950, Starmach 1974). Traditionally, Cryptomonas species...