''Trachelomonas'' is a genus of swimming, free-living
euglenoid
Euglenids (euglenoids, or euglenophytes, formally Euglenida/Euglenoida, ICZN, or Euglenophyceae, ICBN) are one of the best-known groups of flagellates, which are excavate eukaryotes of the phylum Euglenophyta and their cell structure is typical o ...
s characterized by the presence of a shell-like covering called a
lorica.
Details of lorica structure determine the classification of distinct species in the genus.
[ The lorica can exist in spherical, elliptical, cylindrical, and pyriform (pear-shaped) forms. The lorica surface can be smooth, punctuate or striate and range from hyaline, to yellow, or brown. These colors are due to the accumulation of ]ferric hydroxide
Iron(III) oxide-hydroxide or ferric oxyhydroxideA. L. Mackay (1960): "β-Ferric Oxyhydroxide". ''Mineralogical Magazine'' (''Journal of the Mineralogical Society''), volume 32, issue 250, pages 545-557. is the chemical compound of iron, oxygen, ...
and manganic oxide deposited with the mucilage and minerals that comprise the lorica. In ''Trachelomonas'', the presence of a lorica obscures cytoplasmic details of the underlying cell. In each ''Trachelomonas'' cell, there is a gap at the apex of the lorica from which the flagellum protrudes. Thickening around this gap results in a rim-like or collar-like appearance. During asexual reproduction, the nucleus divides yielding two daughter cells one of which exits through the opening in the lorica. This new cell then synthesizes its own new lorica.
History of Knowledge
''Trachelomonas'' was first described by C. G. Ehrenberg in 1834.[Guiry, M. D.; Guiry, G. M. (2012). “Trachelomonas Ehrenberg, 1834”. Retrieved March 5, 2019, fro]
session=abv4:AC1F11E20766f396C8RX21DDBA4A
/ref> Its separation from the genus ''Strombomonas'' occurred in 2008 with the discovery of five subclades within ''Trachelomonas'' through nuclear SSU and LSU rDNA analyses.[Ciugulea, Ionel; Nudelman, María A.; Brosnan, Stacy; Triemer, Richard E. (2008). “Phylogeny of the euglenoid loricate genera Trachelomonas and Strombomonas (Euglenophyta) inferred from nuclear SSU and LSU rDNA”. Journal of Phycology. 44 (2): 406-418]
doi: 10.1111/j.1529-8817.2008.00472.x
/ref>
Habitat and Ecology
''Trachelomonas'' is a common, cosmopolitan genus found in acidic to neutral fresh water
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 include ...
(pH 4.5-7), often in habitats rich in iron and manganese, and pools rich in organic matter
Organic matter, organic material, or natural organic matter refers to the large source of carbon-based compounds found within natural and engineered, terrestrial, and aquatic environments. It is matter composed of organic compounds that have c ...
such as peat. These euglenoids have also been observed to prefer warm, eutrophic waters, increasing in abundance during harmful algal blooms
A harmful algal bloom (HAB) (or excessive algae growth) is an algal bloom that causes negative impacts to other organisms by production of natural algae-produced toxins, mechanical damage to other organisms, or by other means. HABs are sometimes ...
of ''Planktothrix agardhii''. Most species are photosynthetic; therefore, contributing to global primary production
In ecology, primary production is the synthesis of organic compounds from atmospheric or aqueous carbon dioxide. It principally occurs through the process of photosynthesis, which uses light as its source of energy, but it also occurs through c ...
and some species have been observed to be osmotrophs, having the ability to assimilate nutrients from its environment.
Description
Trachelomonads are free-swimming, solitary, photosynthetic flagellates ranging in size from 5-100 um, with an ovoid shape, sharing similar morphological characteristics with its sister group, ''Strombomonas''. These cells are enclosed in a rigid, shell-like envelope, made up of minerals and polysaccharide
Polysaccharides (), or polycarbohydrates, are the most abundant carbohydrates found in food. They are long chain polymeric carbohydrates composed of monosaccharide units bound together by glycosidic linkages. This carbohydrate can react with wa ...
mucilage, with a defined collar or truncate extension that surrounds an anterior
Standard anatomical terms of location are used to unambiguously describe the anatomy of animals, including humans. The terms, typically derived from Latin or Greek roots, describe something in its standard anatomical position. This position prov ...
apical pore where the flagellum emerges from, also known as a lorica. The lorica can be distinguished between different species by the orientation of spines or other ornamentations, such as pores, warts or ridges, and can range from being colourless to orange/brown or even black based on the nutrients in their surroundings.[Trachelomonas Ehrenberg. (n.d.). Retrieved March 5, 2019, from](_blank)
/ref>
Most species are phototrophic, having a characteristic green colour due to the discoid or flattened, shield-like chloroplast
A chloroplast () is a type of membrane-bound organelle known as a plastid that conducts photosynthesis mostly in plant and algal cells. The photosynthetic pigment chlorophyll captures the energy from sunlight, converts it, and stores it in ...
, which usually bears sheathed, projecting or naked 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. The few species that are osmotrophic, lack chloroplasts; therefore, they are colourless. Similar to other euglenoids, the cell has many paramylon
Paramylon is a carbohydrate similar to starch. The chloroplasts found in ''Euglena'' contain chlorophyll which aids in the synthesis of carbohydrates to be stored as starch granules and paramylon. Paramylon is made in the pyrenoids of ''Euglena'' ...
bodies that are used for the storage of starch
Starch or amylum is a polymeric carbohydrate consisting of numerous glucose units joined by glycosidic bonds. This polysaccharide is produced by most green plants for energy storage. Worldwide, it is the most common carbohydrate in human diets ...
; these can be a distinguishing trait for species with similar lorica structures. The structure and ornamentation of the lorica is very dependent on the growth conditions, especially the availability of nutrients. Therefore, the size, shape, collar form and the presence of spines and pores can vary, showing morphological plasticity within species.[Leedale, Gordon F. (2007). “Envelope formation and structure in the Euglenoid genus Trachelomonas”. British Phycological Journal. 10 (1):17-41]
doi: 10.1080/00071617500650031
/ref> This can make it difficult to describe species since morphological features can vary greatly. Trachelomonads also have an eyespot, a feature of photosynthetic euglenoids, located outside the chloroplast with orange to red pigmentation. These cells also have one long emergent flagellum that has previously been identified to emerge from the apical pore, and a shorter flagellum that is within the furrow and not used for motility. Under light microscopy, it is also possible to see condensed chromosome
A chromosome is a long DNA molecule with part or all of the genetic material of an organism. In most chromosomes the very long thin DNA fibers are coated with packaging proteins; in eukaryotic cells the most important of these proteins are ...
s.
Life History
Euglenoids have not been observed to undergo sexual reproduction
Sexual reproduction is a type of reproduction that involves a complex life cycle in which a gamete ( haploid reproductive cells, such as a sperm or egg cell) with a single set of chromosomes combines with another gamete to produce a zygote tha ...
; however, asexual reproduction
Asexual reproduction is a type of reproduction that does not involve the fusion of gametes or change in the number of chromosomes. The offspring that arise by asexual reproduction from either unicellular or multicellular organisms inherit the fu ...
does occur through mitosis
In cell biology, mitosis () is a part of the cell cycle in which replicated chromosomes are separated into two new nuclei. Cell division by mitosis gives rise to genetically identical cells in which the total number of chromosomes is mainta ...
followed by cytokinesis
Cytokinesis () is the part of the cell division process during which the cytoplasm of a single eukaryotic cell divides into two daughter cells. Cytoplasmic division begins during or after the late stages of nuclear division in mitosis and meios ...
.[Esson, H. J.; Leander, B. S. (2006). “A model for the morphogenesis of strip reduction patterns in phototrophic euglenids: Evidence for heterochrony in pellicle evolution”. Evolution Development, 8 (4): 378-388]
doi:10.1111/j.1525-142x.2006.00110.x
/ref> The formation of the lorica after asexual reproduction first occurs through the external skin and then a fibrillar layer is formed between the cell surface and the skin. Then manganese and ferric hydroxide compounds are precipitated on the inner fibrillar layer to produce a thick envelope and the original external skin is lost. However, differences in these processes exist among species.
List of Species
* ''T. acanthopohora'' Stokes
* ''T. americana'' Lemmermann
* ''T. argentina'' Frenguelli
* ''T. bernarddii'' Woloszynka
* ''T. bituricensis'' Wurtz
* ''T. cervicula'' Stokes
* ''T. foliata'' Skvortzov
* ''T. grandis'' K.P. Singh
* ''T. volvocina'' (Ehrenberg) Ehrenberg
References
{{Taxonbar, from=Q146181
Euglenozoa genera
Taxa named by Christian Gottfried Ehrenberg