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Prasinophyceae
The Prasinophytes are a class of unicellular green algae in the Division Chlorophyta.〔 Prasinophytes mainly include marine planktonic species, as well as some freshwater representatives.〔Sym, S. D. and Pienaar, R. N. 1993. The class Prasinophyceae. In Round, F. E. and Chapman, D. J. (Eds) Progress in Phycological Research, Vol. 9. Biopress Ltd., Bristol, pp.
281-376.〕 The prasinophytes are morphologically diverse, including flagellates with one to eight flagella and non-motile (coccoid) unicells. The cells of many species are covered with organic body scales; others are naked.〔 One well known genus is ''Ostreococcus'', considered to be the smallest (ca. 0.95 μm) free-living eukaryote, found in marine waters world wide. Prasinophytes have simple cellular structures, containing a single chloroplast and a single mitochondrion. The genomes are relatively small compared to other eukaryotes (about 12 Mbp for ''Ostreococcus'' and 21 Mbp for ''Micromonas'').
Recent studies agree that the prasinophytes are a non-evolutionary grouping (paraphyletic) of chlorophyte green algae from different clades. Alternative classifications of the chlorophytes have been proposed in which this class is replaced by at least six separate taxa.〔
==Ecology==
A study of photosynthetic gene-sequence diversity (''rbcL'') in the Gulf of Mexico indicated that Prasinophytes are particularly prevalent at the Subsurface Chlorophyll Maximum (SCM) and several different ecotypes of ''Ostreococcus'' have been detected in the environment. These ecotypes were thought to be distinguished in the environment by their adaptation to light intensities. ''O. lucimarinus'' was isolated from a high-light environment and observed year-round in the coastal North Pacific Ocean. RCC141 was considered low-light, because it was isolated from the lower euphotic zone. These strains, or ecotypes, were later shown to live in different habitats (open-ocean or mesotrophic) and their distributions do not appear to be connected to light availability. ''O. tauri'' was isolated from a coastal lagoon and appears to be light-polyvalent. Genetic data indicates that distinct molecular differences exist between the different ecotypes that have been detected.
抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』
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