''Nematodinium'' is a genus of athecate marine

dinoflagellate The Dinoflagellates (), also called Dinophytes, are a monophyletic group of single-celled eukaryotes constituting the phylum Dinoflagellata and are usually considered protists. Dinoflagellates are mostly marine plankton, but they are also commo ...

s. Roughly ovoid in shape, their defining characteristic is the presence of

nematocysts A cnidocyte (also known as a cnidoblast) is a type of cell containing a large secretory organelle called a ''cnidocyst'', that can deliver a sting to other organisms as a way to capture prey and defend against predators. A cnidocyte explosively ...

, from which their name is derived. They are part of the Warnowiacaea family that are famous for the

ocelloid An ocelloid is a subcellular structure found in the family (biology), family Warnowiaceae (warnowiids), which are members of a group of unicellular organisms known as dinoflagellates. The ocelloid is analogous in structure and function to the e ...

, an eye-like organelle that responds to light.

Etymology

The name of the genus comes from Charles A. Kofoid and Olive Swezy (1921) to describe the characteristic feature of the genus: the presence of

, small explosive

extrusome Extrusomes are membrane-bound organelles found in eukaryotic cells that are capable of discharging material contained within to the exterior of the cell. Due to the diversity in structure and function, it is unlikely that different types of extruso ...

organelles that are similar to mucocysts in size and shape.

Type species

The type species of ''Nematodinium'' is ''Nematodinium partitum.'' Kofoid and Swezy first described the genus ''Nematodinium'' in 1921. They described two novel species of ''Nematodinium'': ''N. partitum'', ''N. torpedo'', as well as ''N. armatum'' which had first been observed by Dogiel in 1906.

Habitat

''Nematodinium'' are very rare and fragile, making them challenging both to culture and to study as they will change morphologies or die under light microscopy. Therefore, most of the information regarding their morphology is determined directly from field samples. They have been caught and seen along the eastern and western coasts of

North America North America is a continent in the Northern Hemisphere, Northern and Western Hemisphere, Western hemispheres. North America is bordered to the north by the Arctic Ocean, to the east by the Atlantic Ocean, to the southeast by South Ameri ...

, the western coast of the

United Kingdom The United Kingdom of Great Britain and Northern Ireland, commonly known as the United Kingdom (UK) or Britain, is a country in Northwestern Europe, off the coast of European mainland, the continental mainland. It comprises England, Scotlan ...

, and the waters of

Denmark Denmark is a Nordic countries, Nordic country in Northern Europe. It is the metropole and most populous constituent of the Kingdom of Denmark,, . also known as the Danish Realm, a constitutionally unitary state that includes the Autonomous a ...

. They are found exclusively in marine environments and are seen more abundantly in higher temperatures, such as within the range of . They have yet to be observed feeding, but cells collected from the ocean contained food vacuoles with

trichocyst A trichocyst is an organelle found in certain ciliates and dinoflagellate The Dinoflagellates (), also called Dinophytes, are a monophyletic group of single-celled eukaryotes constituting the phylum Dinoflagellata and are usually considered pr ...

s, which are found in

s, suggesting ''Nematodinium'' eat

s. ''Nematodinium'' species can be either photosynthetic or non-photosynthetic. ''Nematodinium armatum'', and ''Nematodinium parvum'' are

photosynthetic Photosynthesis ( ) is a Biological system, system of biological processes by which Photoautotrophism, photosynthetic organisms, such as most plants, algae, and cyanobacteria, convert light energy, typically from sunlight, into the chemical ener ...

, while the other species are not. However, this is controversial due to the complexity of differentiating between different species, with some claiming that ''Nematodinium parvum'' is the only photosynthetic ''Nematodinium'' species.

Description

Morphology

The size of the organism depends on the species but ranges from 30 μm to 100 μm in length. Their width ranges between 25 and 70 μm.

Characteristic organelles

Going around the outside of ''Nematodinium'' cells is a cingulum, a belt-like structure that winds around 1.2-2.5 times, depending on the species. The

nucleus Nucleus (: nuclei) is a Latin word for the seed inside a fruit. It most often refers to: *Atomic nucleus, the very dense central region of an atom *Cell nucleus, a central organelle of a eukaryotic cell, containing most of the cell's DNA Nucleu ...

is large and found in the center of the cell, and in some species even reaches from apex to the bottom of the cell. Not all species of ''Nemotodinium'' have a

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 ...

. The chloroplasts in ''Nematodinium parvum'' are net-like and arranged as thin lobes that go around the perimeter of the cell.

Ocelloid

''Nemotodinium'' has an eyespot made of a lens and pigment cup with a light sensitive retinoid, now known as the

. The refractive index of the lens was measured and it was found that the retinoid focuses the light coming in from outside of the cell. When the first ''Warnowiid'' was described, the researchers had assumed the cell had grabbed the eye from a decaying jellyfish. The ocelloid is reminiscent of multicellular camera

eye An eye is a sensory organ that allows an organism to perceive visual information. It detects light and converts it into electro-chemical impulses in neurons (neurones). It is part of an organism's visual system. In higher organisms, the ey ...

s as have developed in vertebrates. They consist of a

melanosome A melanosome is an organelle found in animal cells and is the site for synthesis, storage and transport of melanin, the most common light-absorbing pigment found in the animal kingdom. Melanosomes are responsible for color and photoprotectio ...

, which is similar to a retinal body, made from

plastid A plastid is a membrane-bound organelle found in the Cell (biology), cells of plants, algae, and some other eukaryotic organisms. Plastids are considered to be intracellular endosymbiotic cyanobacteria. Examples of plastids include chloroplasts ...

s that contain

peridinin Peridinin is a light-harvesting apocarotenoid, a pigment associated with chlorophyll and found in the peridinin-chlorophyll-protein (PCP) light-harvesting complex in dinoflagellates, best studied in '' Amphidinium carterae''. Biological signific ...

, a

carotenoid Carotenoids () are yellow, orange, and red organic pigments that are produced by plants and algae, as well as several bacteria, archaea, and fungi. Carotenoids give the characteristic color to pumpkins, carrots, parsnips, corn, tomatoes, cana ...

compound, likely acquired from the

endosymbiosis An endosymbiont or endobiont is an organism that lives within the body or cells of another organism. Typically the two organisms are in a mutualism (biology), mutualistic relationship. Examples are nitrogen-fixing bacteria (called rhizobia), whi ...

red algae Red algae, or Rhodophyta (, ; ), make up one of the oldest groups of eukaryotic algae. The Rhodophyta comprises one of the largest Phylum, phyla of algae, containing over 7,000 recognized species within over 900 Genus, genera amidst ongoing taxon ...

. The melanosome is connected to a hyalosome, a translucent

cornea The cornea is the transparency (optics), transparent front part of the eyeball which covers the Iris (anatomy), iris, pupil, and Anterior chamber of eyeball, anterior chamber. Along with the anterior chamber and Lens (anatomy), lens, the cornea ...

-like and lens-like structure built from mitochondria. Under 505 nm (green) light, the retinal body fluoresces red, indicating the presence of

chlorophyll Chlorophyll is any of several related green pigments found in cyanobacteria and in the chloroplasts of algae and plants. Its name is derived from the Greek words (, "pale green") and (, "leaf"). Chlorophyll allows plants to absorb energy ...

. Additionally, the cornea-like layer of the ocelloid was composed of

mitochondria A mitochondrion () is an organelle found in the cells of most eukaryotes, such as animals, plants and fungi. Mitochondria have a double membrane structure and use aerobic respiration to generate adenosine triphosphate (ATP), which is us ...

. The

disassembles when the cell is dividing, whereas the hyalosome is remade after the daughter cells split.

Nematocyst

Most ''Nemotodinium'' have their hallmark nematocysts, small ballistic

s used for predation. The ''Nematodidium'' nematocyst contains a ring of subcapsules in concentric rings. The mechanism of their eruption is still uncertain, but it has been observed that there is a release of a membrane with a lattice structure potentially due to pressure created by capsule walls.

Ocelloid, melanosome, and hyalosome division during asexual division

First, the melanosome divides into two portions and the hyalosome breaks down. During the formation of the two daughter cells but before their separation, the melanosome sections separate, with one part moving to the antapex and the other remaining in the original position of the non-dividing cell. Lastly, just before

cytokinesis Cytokinesis () is the part of the cell division process and part of mitosis 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 ...

, the hyalosome, melanosome, and ocelloid had grown to the size that would be seen in single cells. Each daughter cell contains a newly formed ocelloid. Sexual stages have not been observed.

Practical importance

''Nematodinium'', like other Warnowiaceaea, are relevant because of their ocelloids which are of interest for studying the development and evolution of specialized

organelle In cell biology, an organelle is a specialized subunit, usually within a cell (biology), cell, that has a specific function. The name ''organelle'' comes from the idea that these structures are parts of cells, as Organ (anatomy), organs are to th ...

s that can focus light and might lead to information regarding the

evolution Evolution is the change in the heritable Phenotypic trait, characteristics of biological populations over successive generations. It occurs when evolutionary processes such as natural selection and genetic drift act on genetic variation, re ...

of eyes. As

protist A protist ( ) or protoctist is any eukaryotic organism that is not an animal, land plant, or fungus. Protists do not form a natural group, or clade, but are a paraphyletic grouping of all descendants of the last eukaryotic common ancest ...

s, they are important for studies on other single-celled organisms.

List of species

There are six species recognized in this genus:

References

{{Taxonbar, from=Q25364751 Gymnodiniales Dinoflagellate genera Taxa described in 1921