Chlorodendrales are an order of green,

flagella A flagellum (; ) is a hairlike appendage that protrudes from certain plant and animal sperm cells, and from a wide range of microorganisms to provide motility. Many protists with flagella are termed as flagellates. A microorganism may have f ...

ted,

theca In biology, a theca (plural thecae) is a sheath or a covering. Botany In botany, the theca is related to plant's flower anatomy. The theca of an angiosperm consists of a pair of microsporangia that are adjacent to each other and share a commo ...

te, unicellular

eukaryote Eukaryotes () are organisms whose cells have a nucleus. All animals, plants, fungi, and many unicellular organisms, are Eukaryotes. They belong to the group of organisms Eukaryota or Eukarya, which is one of the three domains of life. Bact ...

s, within the

green algae The green algae (singular: green alga) are a group consisting of the Prasinodermophyta and its unnamed sister which contains the Chlorophyta and Charophyta/ Streptophyta. The land plants ( Embryophytes) have emerged deep in the Charophyte alg ...

class Chlorodendrophyceae.Becker, B., Marin, B. and Melkonian, M. 1994: Structure, composition, and biogenesis of prasinophyte cell coverings. Protoplasma. 181: 233-244. 10.1007/BF01666398See the NCBIbr>webpage on Chlorodendrales
Data extracted from the

Prasinophyceae The prasinophytes are a group of unicellular green algae. 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 ...

are defined by their cellular scales which are composed of

carbohydrate In organic chemistry, a carbohydrate () is a biomolecule consisting of carbon (C), hydrogen (H) and oxygen (O) atoms, usually with a hydrogen–oxygen atom ratio of 2:1 (as in water) and thus with the empirical formula (where ''m'' may or ...

s, and Chlorodendrales are unique within this group due to these scales forming a fused thecal wall. 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. Species within Chlorodendrales live in both marine and fresh water habitats, occupying both

benthic The benthic zone is the ecological region at the lowest level of a body of water such as an ocean, lake, or stream, including the sediment surface and some sub-surface layers. The name comes from ancient Greek, βένθος (bénthos), meaning "t ...

and

plankton Plankton are the diverse collection of organisms found in water (or air) that are unable to propel themselves against a current (or wind). The individual organisms constituting plankton are called plankters. In the ocean, they provide a cr ...

ic food webs. 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 Fresh water or freshwater is any naturally occurring liquid or frozen water containing low concentrations of dissolved salts and other total dissolved solids. Although the term specifically excludes seawater and brackish water, it does in ...

ecosystems around the world, including locations such as the salt plains of

Goa Goa () is a state on the southwestern coast of India within the Konkan region, geographically separated from the Deccan highlands by the Western Ghats. It is located between the Indian states of Maharashtra to the north and Karnataka to th ...

India India, officially the Republic of India ( Hindi: ), is a country in South Asia. It is the seventh-largest country by area, the second-most populous country, and the most populous democracy in the world. Bounded by the Indian Ocean on the ...

.Arora, M., Anil, A.C., Leliaert, F., Delany, J. and Mesbahi, E. 2013: Tetraselmis indica (Chlorodendrophyceae, Chlorophyta), a new species isolated from salt pans in Goa, India. European Journal of Phycology. 48: 61-78. 10.1080/09670262.2013.768357 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 plant The Embryophyta (), or land plants, are the most familiar group of green plants that comprise vegetation on Earth. Embryophytes () have a common ancestor with green algae, having emerged within the Phragmoplastophyta clade of green algae as sist ...

s in terrestrial environments.Norris, R.E., Hori, T., and Chihara, M. 1980: Revision of the Genus Tetraselmis (Class Prasinophyceae). Bot. Mag. Tokyo. 93: 317-339. 10.1007/BF02488737 Primary producers are consumed by primary consumers such as

zooplankton Zooplankton are the animal component of the planktonic community ("zoo" comes from the Greek word for ''animal''). Plankton are aquatic organisms that are unable to swim effectively against currents, and consequently drift or are carried along by ...

invertebrate Invertebrates are a paraphyletic group of animals that neither possess nor develop a vertebral column (commonly known as a ''backbone'' or ''spine''), derived from the notochord. This is a grouping including all animals apart from the chordate ...

larva A larva (; plural larvae ) is a distinct juvenile form many animals undergo before metamorphosis into adults. Animals with indirect development such as insects, amphibians, or cnidarians typically have a larval phase of their life cycle. Th ...

e, and

heterotroph A heterotroph (; ) is an organism that cannot produce its own food, instead taking nutrition from other sources of organic carbon, mainly plant or animal matter. In the food chain, heterotrophs are primary, secondary and tertiary consumers, but ...

protist A protist () is any eukaryotic organism (that is, an organism whose cells contain a cell nucleus) that is not an animal, plant, or fungus. While it is likely that protists share a common ancestor (the last eukaryotic common ancestor), the e ...

s species. Most species within this group are free-living, however some species have become photosynthetic

symbiont Symbiosis (from Greek , , "living together", from , , "together", and , bíōsis, "living") is any type of a close and long-term biological interaction between two different biological organisms, be it mutualistic, commensalistic, or paras ...

s 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 In biology and ecology, abiotic components or abiotic factors are non-living chemical and physical parts of the environment that affect living organisms and the functioning of ecosystems. Abiotic factors and the phenomena associated with them under ...

conditions, such as ambient temperature, the amount of sunlight, and nutrient concentrations. 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.

Cell 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. Cells can be round, ovoid, elliptical, flattened, or compressed; there is great diversity in Chlorodendrales cells.

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. All Prasinophyceae lineages produce these external scales within the

Golgi apparatus The Golgi apparatus (), also known as the Golgi complex, Golgi body, or simply the Golgi, is an organelle found in most eukaryotic cells. Part of the endomembrane system in the cytoplasm, it packages proteins into membrane-bound vesicles ...

, and secrete the scales via the

endomembrane system The endomembrane system is composed of the different membranes (endomembranes) that are suspended in the cytoplasm within a eukaryotic cell. These membranes divide the cell into functional and structural compartments, or organelles. In eukaryote ...

. 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. In Chlorodendrales lineages, these scales fuse after secretion to produce the thecal wall, in which individual scales bind by cross-linking to one another. The flagellar scales and the cell body scales are structurally and functionally different, the main difference being the fusion of cell-body scales. The scales also differ in size, shape, and macromolecular composition. 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. This also means that cell body and flagellar scale production occurs separately.

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. 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. These thecate features are genetically determined, and thus, they are a consistent and reliable characteristic that will not be influenced by environmental factors.

Genera within Chlorodendrales

There are two genera within the order Chlorodendrales, ''

Tetraselmis ''Tetraselmis'' is a genus of phytoplankton. ''Tetraselmis'' is a green algal genus within the order Chlorodendrales, and they are characterized by their intensely-colored green chloroplast, their flagellated cell bodies, the presence of a pyreno ...

'' and '' Scherffelia''. Both species are green, photoautotrophs, flagellated, and thecate. The difference between the two genera is the presence or absence of

pyrenoid Pyrenoids are sub-cellular micro-compartments found in chloroplasts of many algae,Giordano, M., Beardall, J., & Raven, J. A. (2005). CO2 concentrating mechanisms in algae: mechanisms, environmental modulation, and evolution. Annu. Rev. Plant Bio ...

s; ''Tetraselmis'' contains pyrenoids and ''Scherffelia'' does not. Flagella within the two genera are distinct in composition and morphology from species to species, which can be used to infer taxonomy and identification. Both genera 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. 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.

Phylogenetic studies

Researchers have collected and analyzed molecular data from 13 prasinophyte taxa to better construct the

phylogenetic In biology, phylogenetics (; from Greek φυλή/ φῦλον [] "tribe, clan, race", and wikt:γενετικός, γενετικός [] "origin, source, birth") is the study of the evolutionary history and relationships among or within groups o ...

relationship of early branching green alga.Nakayama, T., Marin, B., Kranz, H.D., Surek, B., Huss, V.A., Inouye, I. and Melkonian, M. 1998: The Basal Position of Scaly Green Flagellates among the Green Algae (Chlorophyta) is Revealed by Analyses of Nuclear-Encoded SSU rRNA Sequences. Protistology. 149: 367-380. 10.1016/S1434-4610(98)70043-4 Phylogenetic analysis of the small subunit ribosomal-RNA sequence was performed using distance, parsimony, and likelihood statistical tests. The analyses showed four independent prasinophyte groups, in which these lineages represented the earliest divergences among the

Chlorophyta Chlorophyta or Prasinophyta is a taxon of green algae informally called chlorophytes. The name is used in two very different senses, so care is needed to determine the use by a particular author. In older classification systems, it refers to a ...

. 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. However, the diverging order of this group remains unclear.

References

{{Taxonbar, from=Q3730785, from2=Q21025810 Chlorophyta orders Chlorodendrophyceae