# Gyromitus

Gyromitus (pronounced [ʤɑɪroʊmɑɪtʌs], H. Song, personal communication, February 19, 2023), is a biflagellated thaumatomonas cercozoan found in fresh water. Gyromitus was first discovered in 1939, but, there is still, to this day, very little research done on this organism. The body of the organism is covered in small siliceous oval scales. The two flagella extend from an anterior depression and are used for swimming, not gliding. On occasion this organism can form pseudopods where there are breaks in the silliceous armor, on the ventral side. There are two common species: Gyromitus cordiformis and Gyromitus disomatus.

## Etymology

Although there is no specific information on the etymology of Gyromitus in the original description, each part is a simple Greek word that is defined as follows: ‘Gyro’ means to turn or circle, likely in reference to the locomotion of the organism. The next part ‘mitus’ means strong or powerful. This is likely in reference to the hard exterior body armor that is characteristic of the Gyromitus genus.

## Type Species

The type species for the genus Gyromitus is Gyromitus disomatus Skuja.

## History of Knowledge

Gyromitus disomatus was first identified in 1939 by Heinrich Leonhards Skuja from a freshwater environment in Latvia. He also discovered a second Gyromitus species in 1948, Gyromitus cordiformis. A third putative Gyromitus species was discovered by Hilary Belcher and Erica Swale in New Zealand in 1975. This species was named Gyromitus limax, but the species was later reclassified as Peregrinia by Cavalier-Smith. There is currently some debate about the correct classification of this organism and it is regarded as synonymous to Peregrinia limax. Another study was conducted in 1979 in fresh water environments in Ontario, Canada. This study was conducted by Kennith H. Nicholls, who believed he had found Gyromitus limax. Unfortunately, of the species surveyed from six Ontario lakes none of them were a perfect match to Gyromitus limax. Although Gyromitus was found in the Ontario lakes, the identification of species remains inconclusive. The specific positions of contractile vacuoles are the defining characteristic of the species cordiform and limax. Unfortunately, in the 1979 study, Nicholls did not record any of the specific anatomical positions of the features he was observing and so we cannot conclude anything new about the genus from this experiment. As more information has been discovered about species that share some genetic information with the genus Gyromitus there have been new organizations of the taxonomy. The most recent modifications to the taxonomic placement of the genus were done in 2011 by Thomas Cavalier-Smith, who concluded that it is a thaumatomonas cercozoan (Rhizaria) using molecular data.

## Habitat and Ecology

The original study where Gyromitus was first discovered was conducted in Latvia. This is a freshwater species that has been found in lakes in Latvia, New Zealand, Ontario, Canada, Argentina, Nigeria, and the United Kingdom. There is very little information available as to where within freshwater environments these organisms exist, however, most of them have been found at depth within these waters.

## Description of the Organism

Gyromitus is a heart shaped (cordiform) biflagellated free-swimming cell. It is roughly 15–20 um in length, and roughly 11–19 um in width. The exterior of the organism is covered in small oval shaped siliceous scales that are arranged in a pattern that forms armour around the entire cell. There is a small gap in the silica scales near the anterior end of the cell where on occasion pseudopods can form. The armour forms a microporous membrane that allow the diffusion of molecules smaller than 2 nm across the membrane. A cylindrical structure runs along the anterior side of the cell and is made up 4–8 pores, which allow the diffusion or engulfment of larger molecules. This organism has been observed in most instances to be barely metabolic. This organism has one standard nucleus. The mitochondria have tubular cristae. The formation of the silica scales is associated with the mitochondria and are then transported to their exterior location through transport vesicles, although the exact mechanisms for this process are still unknown. On occasion certain species of Gyromitus can form pseudopods from a small gap in the silica scales on the posterior end of the organism. The pseudopods are used for locomotion and occasionally the species can transform completely into an amoeboid form with the complete dissolution of the flagellum. The position of contractile vacuoles within the cell is a defining characterisic that can be used distinguish between Gyromitus cordiformas and Gyromitus disomatus. The life stages of this organism have not been studied in much depth but so far Gyromitus appears to exist in a biflagellated stage for the majority of its life. There are a few instances where the amoeboid form has been observed. There is no evidence so far to point to the existence of a cyst life stage.

## Fossil History

Gyromitus has a brief fossil history dating back to its discovery in the 1930s. This species was found in Latvia both as a live form and in fossil records, in the form of silica scales, although very limited information is available on this topic

## List of Species

Gyromitus disomatus
Gyromitus cordiformas