{{Short description|Order of algae}} {{Automatic taxobox |image=Bacillario008.png |image_alt=Tetraselmis suecica |image_caption=''Tetraselmis suecica'' | parent_authority = Massjuk | taxon = Chlorodendrales | authority = Melkonian | subdivision_ranks = Families | subdivision = * Chlorodendraceae * †Pterosphaeridiaceae }}
'''Chlorodendrales''' are an order of green, flagellated, thecate eukaryotes, within the green algae class '''Chlorodendrophyceae'''.<ref name="auto">{{cite journal|doi=10.1007/BF01666398 |title=Structure, composition, and biogenesis of prasinophyte cell coverings |date=1994 |last1=Becker |first1=B. |last2=Marin |first2=B. |last3=Melkonian |first3=M. |journal=Protoplasma |volume=181 |issue=1–4 |pages=233–244 |bibcode=1994Prpls.181..233B }}</ref><ref>See the NCBI [https://www.ncbi.nlm.nih.gov/Taxonomy/Browser/wwwtax.cgi?mode=Info&id=35426 webpage on Chlorodendrales]. Data extracted from the {{cite web | url=https://ftp.ncbi.nih.gov/pub/taxonomy/ | title=NCBI taxonomy resources | publisher=National Center for Biotechnology Information | access-date=2007-03-19}}</ref> Prasinophyceae are defined by their cellular scales which are composed of carbohydrates, and Chlorodendrales are unique within this group due to these scales forming a fused thecal wall.<ref name="auto"/> Cells of Chlorodendrales are completely covered in scales, which fuse around the cell body producing the theca, but remain individually separated on the flagella, of which there are typically four per cell.<ref name="auto"/> Species within Chlorodendrales live in both marine and fresh water habitats, occupying both benthic and planktonic food webs.<ref name="auto"/> Additionally, they are photoautotrophs, meaning they produce their own food through the conversion of sunlight into chemical energy.
==Habitat and ecology== Species within Chlorodendrales are found in marine and freshwater ecosystems around the world, including locations such as the salt plains of Goa, India.<ref name="auto1">{{cite journal|doi=10.1080/09670262.2013.768357 |title=''Tetraselmis indica'' (Chlorodendrophyceae, Chlorophyta), a new species isolated from salt pans in Goa, India |date=2013 |last1=Arora |first1=Mani |last2=Anil |first2=Arga Chandrashekar |last3=Leliaert |first3=Frederik |last4=Delany |first4=Jane |last5=Mesbahi |first5=Ehsan |journal=European Journal of Phycology |volume=48 |issue=1 |pages=61–78 |bibcode=2013EJPhy..48...61A }}</ref> Species occupy niches within planktonic and benthic food webs, in which all species are photoautotrophic and have an ecosystem and trophic role similar to land plants in terrestrial environments.<ref name="auto2">{{cite journal|doi= 10.1007/BF02488737 |title= Revision of the genus ''Tetraselmis'' (Class Prasinophyceae) |date= 1980 |last1= Norris |first1= Richard E. |last2= Hori |first2= Terumitsu |last3= Chihara |first3= Mitsuo |journal= The Botanical Magazine Tokyo |volume= 93 |issue= 4 |pages= 317–339 |bibcode= 1980JPlR...93..317N }}</ref> Primary producers are consumed by primary consumers such as zooplankton, invertebrate larvae, and heterotrophic protists species. Most species within this group are free-living, however some species have become photosynthetic symbionts in animals; the animal species that can be in symbiosis with Chlorodendrales is limited, due to their need for sunlight for photosynthetic processes. Chlorodendrales populations in natural settings tend to experience extreme fluctuations in population numbers due to seasonal changes in abiotic conditions, such as ambient temperature, the amount of sunlight, and nutrient concentrations.<ref name="auto2"/> This leads to what has been classified as "blooms," which is the rapid increase in algae numbers during the spring and autumn months because of high light activity and the turnover of nutrients within the water column. It results from the high amount of sunlight, and the mixing of the water layers which resupplies the upper photosynthetic layer with nutrients, allowing for primary productivity to flourish.
==Morphology== Cell shape and size of Chlorodendrales cells varies depending on the species. The cells range greatly in size from species to species, with an upper limit of ~25 μm in length.<ref name="auto1"/> Cells can be round, ovoid, elliptical, flattened, or compressed; there is great diversity in Chlorodendrales cells.<ref name="auto1"/>
===Flagellar and cell-body scales=== Chlorodendrales scales are unique from other Prasinophyceae lineages because the scales fuse to form a theca, which acts as an exterior protective casing for the cell.<ref name="auto"/> All Prasinophyceae lineages produce these external scales within the Golgi apparatus, and secrete the scales via the endomembrane system.<ref name="auto"/> Vesicles budding from the trans-Golgi face carry the scales to the cell surface, and upon fusion release the scales to the external cell face.<ref name="auto"/> In Chlorodendrales lineages, these scales fuse after secretion to produce the thecal wall, in which individual scales bind by cross-linking to one another.<ref name="auto"/>
The flagellar scales and the cell body scales are structurally and functionally different, the main difference being the fusion of cell-body scales.<ref name="auto"/> The scales also differ in size, shape, and macromolecular composition.<ref name="auto"/> The Golgi apparatus is only capable of producing one scale-type at a time, thus, species with multiple scale-types must have different phases of thecal development separated by time and space.<ref name="auto"/> This also means that cell body and flagellar scale production occurs separately.<ref name="auto"/>
===Scales used for taxonomic purposes and species identification=== The thecae of Chlorodendrales species are often unique, and it is an important character for species identification and classification.<ref name="auto"/> Thecate features vary greatly from species to species, in which thecae can vary between 1-5 scale layers, in scale shape, in scale size, and in molecular composition/ultrastructure.<ref name="auto"/> These thecate features are genetically determined, and thus, they are a consistent and reliable characteristic that will not be influenced by environmental factors.<ref name="auto"/>
===Genera within Chlorodendrales=== There are three genera within the order Chlorodendrales, ''Tetraselmis'', ''Scherffelia'', and ''Prasinocladus''. ''Tetraselmis'' and ''Scherffelia'' are unicellular, free-swimming organisms, while ''Prasinocladus'' forms colonies of cells attached to surfaces via branched stalks.<ref name=Masjuk>{{cite journal |last=Masjuk |first=N.P. |year=2006 |trans-title=Chlorodendrophyceae class. nov. (Chlorophyta, Viridiplantae) in the Ukrainian flora: I. The volume, phylogenetic relations and taxonomical status |title=Chlorodendrophyceae class. nov. (Chlorophyta, Viridiplantae) у флорі України. І. Обсяг, філогенетичні звʼязки, систематичне положення |journal=Ukrainian Botanical Journal |volume=63 |issue=5 |pages=601–614 |language=uk}}</ref>
''Tetraselmis'' and ''Scherffelia'' differ in the presence/absence of pyrenoids; ''Tetraselmis'' contains pyrenoids and ''Scherffelia'' does not.<ref name="auto2"/> Flagella within the genera are distinct in composition and morphology from species to species, which can be used to infer taxonomy and identification.<ref name="auto"/> Both ''Tetraselmis'' and ''Scherffelia'' produce three types of flagellar scales, in scale combination, and scale patterning, is unique between species. Scales differ mainly in composition and ultrastructure, and these are the main features examined from flagellar scales when identifying species.<ref name="auto"/> The increase in knowledge about the morphological and ultrastructural features of flagellar scales, and the ability to identify species as a result, has been due to the development of advanced microscopy and staining techniques.<ref name="auto"/>
==Phylogenetic studies== Researchers have collected and analyzed molecular data from 13 prasinophyte taxa to better construct the phylogenetic relationship of early branching green alga.<ref name="auto3">{{cite journal|doi= 10.1016/S1434-4610(98)70043-4 |title= The Basal Position of Scaly Green Flagellates among the Green Algae (Chlorophyta) is Revealed by Analyses of Nuclear-Encoded SSU rRNA Sequences |date= 1998 |last1= Nakayama |first1= Takeshi |last2= Marin |first2= Birger |last3= Kranz |first3= Harald D. |last4= Surek |first4= Barbara |last5= Huss |first5= Volker A.R. |last6= Inouye |first6= Isao |last7= Melkonian |first7= Michael |journal= Protist |volume= 149 |issue= 4 |pages= 367–380 |pmid= 23194719 }}</ref> Phylogenetic analysis of the small subunit ribosomal-RNA sequence was performed using distance, parsimony, and likelihood statistical tests.<ref name="auto3"/> The analyses showed four independent prasinophyte groups, in which these lineages represented the earliest divergences among the Chlorophyta.<ref name="auto3"/> The most parsimonious tree created suggests that the Chlorodendrales lineage is a very early diverging group of "core Chlorophytes," of which there are four clades.<ref name="auto3"/> However, the diverging order of this group remains unclear.<ref name="auto3"/>
==References== {{Reflist|1}}
{{Taxonbar|from=Q3730785|from2=Q21025810}}
Category:Chlorophyta orders Category:Chlorodendrophyceae Category:Monotypic plant classes