''Hemiselmis'' is a genus of

cryptomonad The cryptomonads (or cryptophytes) are a group of algae, most of which have plastids. They are common in freshwater, and also occur in marine and brackish habitats. Each cell is around 10–50 μm in size and flattened in shape, with an anteri ...

History of discovery

It was first described by English biologist Mary Parke in 1949. She also described the first species in this genus, ''Hemiselmis rufescens.''

Morphology

''Hemiselmis'' are typically 4 to 9 micrometers long, free-swimming, biflagellate monads. They are generally bean-shaped with the flagella located between 1/3 and 1/2 the cell length from the anterior. A tubular gullet lined with usually two rows of ejectisomes is found to be in the posterior region of the cell. A single plastid and nucleomorph are present, with it possessing the

biliprotein Biliproteins are pigment protein compounds that are located in photosynthesising organisms such as algae and certain insects. They refer to any protein that contains a bilin chromophore. In plants and algae, the main function of biliproteins is t ...

pigment Cr-

phycoerythrin Phycoerythrin (PE) is a red protein-pigment complex from the light-harvesting phycobiliprotein family, present in cyanobacteria, red algae and cryptophytes, accessory to the main chlorophyll pigments responsible for photosynthesis.The red pigment ...

555 or one of Cr-

phycocyanin Phycocyanin is a pigment-protein complex from the light-harvesting phycobiliprotein family, along with allophycocyanin and phycoerythrin. It is an accessory pigment to chlorophyll. All phycobiliproteins are water-soluble, so they cannot exist w ...

, 577, 612 and 630. For example, ''Hemiselmis pacifica'' possesses Cr-PC577, and Cr-PC612 is found in ''Hemiselmis virescens'' and ''Hemiselmis tepida''. The chloroplasts are red in color. The species has periplast surrounding the cells below plasma membrane. The periplast consists of internal and superficial plates that have a general shape of hexagons. The ultrastructure of several species is well known. The periplast of ''H. brunnescens'' has crystalline plates and an unusual secondary layer composed of small "sausage-like" fibrils. The nucleomorph is located outside the pyrenoid between the pyrenoid and the nucleus. The flagella are covered with a layer of fibrillary scales overlapping with each other. Serial reconstruction has shown that there is only one mitochondrion per cell.

Reproduction

Reproduction is only known by asexual reproduction. Species of ''Hemiselmis'' remain motile even while dividing.

Movement

''Hemiselmis'' species may easily be overlooked in samples due to their small size and rapid movement, but can be recognized by the special corkscrew swimming motion. It is concluded that the spiral swimming is not because of the irregularity in length or structure of flagella, but because of the dorsoventral flattening of its body. Also, the fact that the flagella are attached at a low point near posterior contributed to the unique swimming pattern observed.

Ecology

Species are generally found in oceanic or coastal marine waters. They are also found in freshwater environment. They are found in a variety of locations on Earth. The locations include Baltic Sea, Caribbean Sea and Isle of Man. Specific temperature ranges and depths to find these species are still not yet classified.

Nucleomorph genome

The nucleomorph genome of ''H. rufescens'' has been studied quite thoroughly. Using pulsed-field gel electrophoresis (PFGE), size of the ''H. rufescens'' nucleomorph genome was estimated to be 580 kb. The most significant discovery so far is the complete sequence of nucleomorph genome of ''Hemiselmis andersenii''. The size of the genome is 0.572 Mbp. The nucleomorph genome shows a complete intron loss, with no spliceosomal introns and genes for splicing RNAs. It is suggested that evolution has driven the loss of introns and modified the shape and function of proteins; minimal functional units are needed to maintain basic eukaryotic cellular processes.

List of species

There are currently 16 identified species. Of the 16 species, 14 are accepted taxonomically. Currently, ''Hemiselmis brunnescens'' and ''Hemiselmis cyclopea'' have unknown status. A complete list is added below. ''Hemiselmis amylifera'' Butcher, 1967 ''Hemiselmis amylosa'' Clay & Kugrens, 1999 ''Hemiselmis andersenii'' Lane & Archibald, 2008 ''Hemiselmis anomala'' Butcher, 1967 ''Hemiselmis brunnescens'' Butcher, 1967 ''Hemiselmis cryptochromatica'' Lane & Archibald, 2008 ''Hemiselmis cyclopea'' Butcher, 1967 ''Hemiselmis oculata'' Butcher, 1967 ''Hemiselmis pacifica'' Lane & Archibald, 2008 ''Hemiselmis parvula'' (Skuja) Butcher, 1967 ''Hemiselmis rotunda'' Butcher, 1967 ''Hemiselmis rufescens'' Parke, 1949 ''Hemiselmis simplex'' Butcher, 1967 ''Hemiselmis tepida'' Lane & Archibald, 2008 ''Hemiselmis vinosa'' (Conrad) Chrétiennot-Dinet, 1990 ''Hemiselmis virescens'' Droop, 1955

References

{{Cryptista Cryptomonad genera