Halteria, sometimes referred to as the jumping oligotrich, is a genus of common planktonic that are found in many freshwater environments. Halteria are easy to locate due to their abundance and distinctive behaviour with observations of Halteria potentially dating back to the 17th century and the discovery of microorganisms. Over time more has been established about their morphology and behavior, which has led to many changes in terms of classification.
Species of Halteria can exist in both a trophic and an encysted form but are most commonly described in the trophic form. Species of Halteria can be identified by their unique jumping movement which is enabled by an equatorial row of stiff cirri that beat in unison, allowing the organism to move very quickly backwards.
Members of the genus Halteria are Heterotroph and serve as important Bacterivore in the habitats they occupy as well as being preyed upon primarily by metazoans. One paper published on December 27 2022 identified Halteria sp. as the first identified "virovore", an organism that can feed on virus. The cells of Halteria are roughly dome shaped and in addition to the equatorial cirri, they possess a collar of cilia around the buccal opening used for feeding and locomotion. The important ecological role played by Halteria as well as its unique locomotion strategy, makes Halteria a genus of interest in different areas of protistology research.
The name Halteria is credited to Félix Dujardin in 1840, who reclassified Trichodina grandinella and Trichodina vorax, which had been previously classified by Müller and Ehrenberg respectively, as H. grandinella and H. vorax. Creating the new genus, Halteria, when the two species were found not to fit the subfamily Vorticellina, under which the genus Trichodina fell. Descriptions of Halteria at this time were still rather vague, focusing on the quick jumping movement that results from the beating of its cirri and the presence of oral cilia.
In 1858, Édouard Claparède and Johannes Lachmann described Halteria grandinella in greater detail. Noting explicitly for the first time, that the cirri are only found in an equatorial belt around the cell. New details relating to the buccal cavity were also discovered; Claparède and Lachmann observed that there was an indentation in a portion of the buccal apparatus and that at this site no oral cilia are present. This means that the oral cilia form an incomplete circle around the buccal cavity, and do not surround it completely as was previously assumed.
Questions on the classification of Halteria have arisen again in more recent years. Halteria have been most commonly classified as a member of the Oligotrich, because they possess the group's characteristic prominent oral cilia arranged in an incomplete circle. However, recent deep sequencing and RNA analysis of Halteria indicate that Halteria may be more closely related to Oxytrichidae than oligotrichs, suggesting the similarity in oral apparatus with oligotrichs is the result of convergent evolution.
The rigid cirri of Halteria, sometimes referred to as jumping bristles, are each 15-25 μm long. The cirri are organized equatorially around the cells in 7-10 longitudinal rows. Each row is in turn organized into four groups of cirri. When species of Halteria beat these cirri in unison, they generate a characteristic jumping motion sufficiently distinct to Halteria that observation of this movement has been considered sufficient for visual identification of Halteria
The cortex of Halteria is composed of four membranes. Two of these membranes, the inner and outer alveolar membranes, cover the flat alveoli which lie entirely beneath the two remaining membranes. The cell membrane sits directly above the outer alveolar membrane and covers the entire cell including the cilia. The perilemma is the fragile outermost membrane seen covering only small portions of the cell. The fragility of the perilemma may be the cause of this distribution as it would be difficult to preserve. Just beneath the membranes of the cortex, the body shape of Halteria is stabilized by microtubules in a basket configuration.
Within Halteria cells, a contractile vacuole is located approximately midway between the anterior and posterior ends of the cell. The mitochondria of Halteria are usually spherical with tubular cristae. Within the mitochondria of H. geleiana, microorganisms have been observed within the matrix. The microorganisms were rod shaped and observed with various lengths and in different numbers. No function or origin is currently known for these microorganisms or whether they are parasitic or symbiotic. Halteria have one micronucleus and a macronucleus with large band-like nucleoli. The macronucleus is oblong in shape while the micronucleus is more globular.
Species of Halteria play a particularly large role in many freshwater habitats as Bacterivore. In a study that used fluorescently labelled bacteria in fishponds to observe protistan bacterivory, ciliate grazing accounted for 56% of total protistan grazing and Halteria, along with two other ciliate genera, Pelagohalteria and Rimostrombidium were responsible approximately 71% of the total ciliate bacterivory. Halteria also act as prey for many metazoan predators. It has been proposed that the characteristic jumping behavior of Halteria was evolved as an escape strategy to avoid such predation. Halteria are also able to act as Virovore and can consume viruses, such as chloroviruses, to fuel growth and division.
Much of the research related to Halteria is focused on their movement and their ecological roles. Halteria acts as a model organism for the study of their jumping movement through ciliary beating. It can be found in abundance in diverse freshwater habitats interacting with other organisms as both predators and prey.
Halteria spend most of the time either stationary or moving smoothly through water propelled by the cilia at their anterior end. The halting jumping movement most associated with Halteria is the result of external stimulus such as currents, which is known because jumping in Halteria has been induced in a laboratory setting. Jumping behavior in Halteria requires 41% of the organism's total metabolic rate, and so employing it too frequently would be an inefficient use of energy.
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