''Strombomonas'' is a genus of free-living

euglenoid Euglenids or euglenoids are one of the best-known groups of eukaryotic flagellates: single-celled organisms with flagella, or whip-like tails. They are classified in the phylum Euglenophyta, class Euglenida or Euglenoidea. Euglenids are commonly ...

s characterized by the presence of a shell-like covering called a lorica. It is found in

freshwater Fresh water or freshwater is any naturally occurring liquid or frozen water containing low concentrations of dissolved salts and other total dissolved solids. The term excludes seawater and brackish water, but it does include non-salty mi ...

habitats, and has a

cosmopolitan distribution In biogeography, a cosmopolitan distribution is the range of a taxon that extends across most or all of the surface of the Earth, in appropriate habitats; most cosmopolitan species are known to be highly adaptable to a range of climatic and en ...

; about 100 species are accepted.

Description

''Strombomonas'' consists of solitary, free-living cells surrounded by a shell, called a lorica. The lorica has an apical opening where the

flagellum A flagellum (; : flagella) (Latin for 'whip' or 'scourge') is a hair-like appendage that protrudes from certain plant and animal sperm cells, from fungal spores ( zoospores), and from a wide range of microorganisms to provide motility. Many pr ...

emerges. The cells themselves are mostly 25–50 μm long and 15–35 μm wide, and are mostly like ''Euglena'' in terms of morphology. They contain numerous greenish

chloroplast A chloroplast () is a type of membrane-bound organelle, organelle known as a plastid that conducts photosynthesis mostly in plant cell, plant and algae, algal cells. Chloroplasts have a high concentration of chlorophyll pigments which captur ...

s with

pyrenoid Pyrenoids are sub-cellular phase-separated 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. ''An ...

s, although this can often be difficult to see through the lorica. The lorica is sac- or vase-shaped, with a neck and tailpiece of varying lengths. The lorica aggregates particles on its outer surface, giving it a scabrous (rough) texture; the lorica also lacks spines, pores or pits, although it may have wrinkles. The lorica start off colorless but can often yellowish to brownish due to the impregnation of iron, silica and manganese compounds.

Taxonomy

''Strombomonas'' was first described by Georges Deflandre in 1930, transferring species out of the similar genus ''

Trachelomonas ''Trachelomonas'' is a genus of swimming, free-living euglenoids characterized by the presence of a shell-like covering called a Lorica (biology), lorica. Details of lorica structure determine the classification of distinct species in the genus. ...

''. In the decades following, ''Strombomonas'' was not always accepted, and was sometimes considered a synonym of ''Trachelomonas''. Currently, however, the two genera are generally accepted. Morphologically, ''Strombomonas'' has loricae without pores or spines, while ''Trachelomonas'' has loricae with pores or spines during at least part of its life cycle. In ''Trachelomonas'' the lorica has a definite "collar" at the anterior, while there in ''Strombomonas'' the lorica has an opening but no definite collar. In addition, the loricae of ''Strombomonas'' are formed from the anterior to the posterior, while in ''Trachelomonas'' the loricae develop evenly throughout the cell. ''Strombomonas'' and ''Trachelomonas'' form

sister clade In phylogenetics, a sister group or sister taxon, also called an adelphotaxon, comprises the closest relative(s) of another given unit in an evolutionary tree. Definition The expression is most easily illustrated by a cladogram: Taxon A and ...

s according to

molecular phylogenetic Molecular phylogenetics () is the branch of phylogeny that analyzes genetic, hereditary molecular differences, predominantly in DNA sequences, to gain information on an organism's evolutionary relationships. From these analyses, it is possible to ...

studies. Within ''Strombomonas'', species delimitation has traditionally relied on lorica morphology, since internal structures like chloroplasts are often difficult to visualize through the lorica. However, the true number of species may be smaller than the number of described species, since the lorica morphology can vary due to environmental conditions leading to the same species being described more than once. Taxonomic revisions using molecular data have started to include other characters, such as the number of chloroplasts and pyrenoid morphology.

References

{{Authority control Euglenozoa genera Euglenozoa