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= Tovellia =

Introduction
Tovellia is a genus of single-celled dinoflagellate that is found primarily in cold, freshwater environments. Like many other dinoflagellates, Tovellia is considered to be a photosynthetic algae. Tovellia cells are spherical and typically measure 20-30 µm in length and 15-25 µm in width. Tovelia can be distinguished from other dinoflagellates by its bright red colouration and prominent peduncle. Some species of Tovellia are known to “bloom” in optimal conditions, turning the bodies of water in which they reside a spectacular red colour.

Etymology
The etymology of Tovellia comes from the name of Lake Tovel in the Italian Alps.

Type Species
Tovellia coronata (Wołoszyńska) Moestrup, K.Lindberg & Daugbjerg 2005

Discovery:
Lake Tovel is a small lake in the Italian Alps that was renowned for turning red in the summer due to an algal bloom of dinoflagellates. The occurrence of this unusual phenomenon stopped in 1964 and an investigation began in 2001 in order to determine the cause of the bloom disappearance. The investigation postulated that the reddening of the lake was due to an influx of nitrogen and phosphorus caused by cattle that grazed in the high pastures near the lake, an issue that has since been resolved by a change in the management of cattle in the area.

The colour change was originally thought to be caused by one species of dinoflagellate (Glenodinium sanguineum) with alternating red and green forms in its life cycle, but further study indicated that there are actually three different species of dinoflagellate algae, two green and one red, present in the lake, with the red being much rarer.

It is now believed that the red colour of the lake is caused by the species Tovellia sanguineum belonging to the novel genus Tovellia.

Classification:
The members of Tovellia originally belonged to the genus Gymnodinium, a group erected by Stein (1878) which included athecate (naked) dinoflagellates, and was intended to separate them from the thecate Peridinium. In 1917, Jadwiga Woloszynska observed thecal plates in several species that were originally included in Gymnodinium, the presence of which were likely missed due to the arrangement of their thecal plates being inconsistent with the system described in other thecate dinoflagellates. In 1951, based on Woloszynska’s observations, R.H. Thompson established the genus Woloszynska in order to include these Gymnodinium-like species which had thecal plates.

The taxonomic status of Tovellia remained relatively untouched until 2003 when Moestrup et al. published a preliminary report suggesting that the genus Woloszynska actually comprised at least four genera, prompting the creation of several novel genera, including Tovellia. Since then, several dinoflagellate species have been reclassified as Tovellia, including Tovellia coronata, Tovellia sanguinea, and Tovellia aveirensis.

Habitat and ecology
Tovellia is found in a variety of aquatic habitats, including lakes, ponds, rivers, and streams. It is very tolerant of cold, even freezing temperatures and thus is often present in high elevation alpine lakes and streams. New and reclassified species of Tovellia have been found in North America, Europe, and Asia.

Tovellia’s ability to produce resting cysts allows it to survive in ice and melt water. It can be found swimming in the water column and also in the sediment of ponds and lakes, as well as attached to rocks and aquatic plants.

Tovellia is believed to be responsible for freshwater “red tide” algal blooms as well as some occurrences of red ice in North America. Blooms of red pigmented Tovellia typically occur when nutrients such as nitrogen and phosphorus are plentiful, although it is uncertain exactly what concentrations lead to the development of this red colour.

Morphology:
Tovellia are unique dinoflagellates whose cells typically measure around 20-30 µm in length and 15-25 µm in width.

The cells of Tovellia are slightly dorsoventrally compressed, nearly spherical in shape and are covered by a theca, which is a protective covering made of cellulose plates. The theca consists of an epicone and hypocone, divided by a cingulum. The epicone is typically slightly larger and longer than the more flattened hypocone. The cingulum is displaced by approximately one cingulum width on the posterior end of the cell. The theca is mainly composed of several pentagonal or hexagonal plates arranged latitudinally, with 5-7 plates on the epicone, and 3-5 on the hypocone. Cells range from bright red to yellowish-green depending on the concentration of photosynthetic pigments, which include chlorophyll a and c, peridinin, diadinoxanthin, dinoxanthin and β-carotene. This concentration is influenced by the availability of nutrients such as nitrogen and phosphorus, although it is uncertain exactly what nutrient concentrations lead to the colour changes seen in Tovellia.

Tovellia has two flagella, which are long, whip-like structures used for movement. The transverse flagellum emerges from the anterior end of the cell and extends forward, while the longitudinal flagellum emerges from the posterior end and trails behind the cell.

Tovellia possesses a unique structure called the peduncle, which is a long, thin extension of the cell body that is used for attachment to substrates. The peduncle emerges near the origin of the flagellar apparatus and is anchored to the substrate by a basal plate and can extend up to several times the length of the cell body. The function of the peduncle is not fully understood, but it is believed to aid in nutrient uptake and help the cell avoid predation.

Inside the cell, Tovellia has a complex system of organelles, including a large nucleus, several small chloroplasts, and a number of mitochondria. The somewhat curved nucleus is located in the hypocone and a prominent eyespot is located next to the sulcus.

Overall, the cellular morphology of Tovellia is characteristic of dinoflagellates, with a distinctive theca and apical groove, two flagella, and a complex system of organelles. Further studies are needed in regard to the feeding behaviour of Tovellia.

Life cycle:
The life cycle of Tovellia, like other dinoflagellates, is complex and includes both sexual and asexual stages. The exact details of the life cycle of Tovellia are not well understood, but it is believed to follow a similar pattern to other members of Dinophyceae.

The asexual reproduction of Tovellia occurs by binary fission, where the cell divides into two to four daughter cells. This process occurs rapidly, and under optimal conditions, Tovellia can produce large numbers of haploid daughter cells, leading to rapid population growth.

Sexual reproduction in Tovellia occurs by a process called syngamy, which involves the fusion of two gametes to form a zygote. The gametes of Tovellia are typically formed by meiosis, which produces four haploid daughter cells. Two of these daughter cells then fuse to form a diploid zygote, which undergoes mitosis to produce a new generation of haploid cells.

During periods of unfavorable environmental conditions, such as nutrient depletion or changes in temperature or salinity, Tovellia may enter a dormant stage known as a cyst. The cyst is a thick-walled structure that protects the organism from harsh conditions and allows it to survive until conditions become more favorable.

List of Species
Tovellia apiculata

Tovellia aveirensis

Tovellia coronata

Tovellia diexiensis

Tovellia dodgei

Tovellia glabra

Tovellia leopoliensis

Tovellia nygaardii

Tovellia paldangensis

Tovellia rinoi

Tovellia rubescens

Tovellia sanguinea

Tovellia stoschii