Dinoflagellates

Several species can grow quickly under specific conditions, causing water blooms or red tides that discolour the water and may harm fish and other organisms. Some dinoflagellates release toxins that are among the most harmful bacteria known.

Characteristics of Dinoflagellates:

Dinoflagellates are single-celled eukaryotic animals that belong to the kingdom Protista and the phylum Dinoflagellata. They are extremely small and are characterised by the presence of two flagella, which allow them to move. Dinoflagellates are named after the Ancient Greek words “dînos” (whirling) and “flagellate” (whip). They are generally marine organisms, but some are also found in freshwater. Dinoflagellates are generally photosynthetic, however some are heterotrophs. Dinoflagellates also cause ocean surface phenomena such as red tides and bioluminescence. In this section, we’ll study more about dinoflagellates and get answers to some essential questions.

Dinoflagellates (Greek o dinos “whirling” and Latin flagellum “whip, scourge”) are a phylum of single-celled eukaryotes[5]. They are often known as algae. Dinoflagellates are found primarily in marine plankton, but they can also be found in freshwater. The population of these organisms changes according on water temperature, salinity, and depth. Many dinoflagellates are photosynthetic, but a significant fraction are mixotrophic, which means they combine photosynthesis with prey ingestion (phagotrophy and myzocytosis).

Dinoflagellates are one of the most diverse groups of marine eukaryotes, yet they are much smaller than diatoms.

[8] Some species are marine organisms’ endosymbionts, and they play an important part in coral reef biology. Other dinoflagellates are predators of protozoa that are not pigmented, and some are parasitic (for example, Oodinium and Pfiesteria). Dinoflagellates produce resting stages known as dinoflagellate cysts or dinocysts as part of their life cycles, and dinoflagellate cysts or dinocysts have been identified in 84 of the 350 freshwater species recorded and slightly more than 10% of the known marine species. Dinoflagellates are alveolates with two flagella that are the primordial stage of bikonts.

In 1753, Henry Baker identified the first modern dinoflagellates as “Animalcules that produce the Sparkling Light in Sea Water,” and Otto Friedrich Müller said the same in 1773.

The name is derived from the Greek word dînos, which means “whirling,” and the Latin word flagellum, which is a diminutive term for a whip or scourge. In the 1830s, German microscopist Christian Gottfried Ehrenberg examined various water and plankton samples and proposed several dinoflagellate species that are still used today, including Peridinium, Prorocentrum, and Dinophysis.

In 1885, Otto Bütschli categorised these dinoflagellates as the flagellate order Dinoflagellata. After the bioluminescent species, botanists classed them as Pyrrophyta or Pyrrophyta (“fire algae”; Greek pyrr(h)os, fire), or Dinophyta. The cryptomonads, eroids, and ellobiopsids have all been included at some point, however only the latter two are now considered close relatives. Dinoflagellates are known to be able to convert from non cyst to cyst-forming mechanisms, making reconstruction of their evolutionary history difficult.

Dinoflagellates are unicellular creatures that have two flagella that protrude from the ventral cell surface (isokont flagellation). They have a ribbon-like transverse flagellum that beats to the left of the cell, as well as a more typical longitudinal flagellum that beats to the right of the cell. [18] [19] [20] The transverse flagellum is a wavy ribbon with only the outer border undulating from base to tip due to the activity of the axoneme that passes along it. On the axonemal edge, simple hairs of varying lengths can be observed. Flagellar movement produces both forward and rotating propulsion. The longitudinal flagellum contains few or no hairs and appears generally normal. It features a wave with one or two phases. Although the distal portion of the flagella protrudes freely behind the cell, it is positioned in surface grooves: the transverse one in the cingulum and the longitudinal one in the sulcus. The two flagella are identified in dinoflagellate species with desmokont flagellation (e.g., Prorocentrum), but they are not joined by grooves.

Thecate (“armoured”) dinoflagellates, as opposed to athecate (“nude”) dinoflagellates, support overlapping cellulose plates to form a type of armour known as the theca or lorica. They appear in a variety of shapes and patterns depending on the species and, in certain circumstances, the stage of the dinoflagellate. This arrangement of thecal plates has always been referred to as tabulation. To express the plate configuration, the plate formula or tabulation formula can be employed. Fibrous extrusomes come in many different shapes and sizes. 

The sulcus is a longitudinal furrow that flows posteriorly from the transverse groove. The transverse flagellum strikes in the cingulum, while the longitudinal flagellum impacts in the sulcus. 

Diversity of Dinoflagellates:

This organisation, together with other morphological and genetic features, implies a close relationship between dinoflagellates, Apicomplexa, and ciliates, which are known collectively as the alveolates.

The presence of three membranes encircling the chloroplasts of most photosynthetic dinoflagellates indicates that they were most likely produced from eaten algae. 

Most photosynthetic organisms have chlorophylls a and c2, the carotenoid beta-carotene, and a trio of xanthophylls that appear to be unique to dinoflagellates, peridinin, dinoxanthin, and diadinoxanthin. Because of these pigments, many dinoflagellates have a golden brown colour. Other pigments, such as fucoxanthin, have been obtained through endosymbiosis by the dinoflagellates Karenia brevis, Karenia mikimotoi, and Karlodinium micrum.  This demonstrates that many endosymbiotic interactions involving previously coloured or secondary colourless species absorbed their chloroplasts. The discovery of plastids in Apicomplexa has led some to hypothesise that they were passed down from a common ancestor, despite the fact that none of the more basic lines had them. Nonetheless, the dinoflagellate cell contains the rough and smooth endoplasmic reticulum, Golgi apparatus, mitochondria, lipid and starch grains, and feeding vacuoles. 

Conclusion

Some athecate species’ internal skeletons are made up of two star-like siliceous components with unknown functions that can be found as microfossils. The first detailed description of the pentasters in Actiniscus pentasterias was provided using SEM microscopy. They are members of the Gymnodiniales suborder Actiniscineae of the Gymnodiniales order.