Stentor (ciliate)

The name Stentor is a reference to the trumpet like shape of the organism, specifically its widened "mouth" or oral apparatus. It is derived from a herald in Greek mythology, who used his booming voice to motivate the Greek soldiers in the Trojan war. == Type species ==

S. muelleri was the first species described in detail as a member of the genus by Christian Gottfried Ehrenberg in 1831. It is found commonly in freshwater habitats and occasionally estuaries, dispersed around the world. It is characterized by its moniliform macronucleus (containing 10-20 macronuclear nodes) and unpigmented cortical granules. Despite lacking pigments like other species, S. muelleri is not colourless but appears brown due to the thickness of the cell. It is typically 0.5 to 2 millimeters in length but can rarely stretch up to 3 millimeters. ==Description==

Stentor can grow up to two millimeters in length, large enough for individuals to be seen by the naked eye. This size combined with their highly motile nature gives Stentor a complex interconnected physiology. The surface of the cell is covered with a protective layer called the pellicle. This layer is secreted by the cell and can be shed and reformed if the organism is stressed. Cilia and motility , 2 - oral pouch, 3 - micronucleus, 4 - macronuclear nodes, 5 - holdfast, 6 - peristome, 7 - gullet, 8 - food vacuole, 9 - contractile vacuole The clear bands of the ectoplasm are where cilia are located. Each clear band houses a kinety, with numerous adjacent cilia longitudinally along the organism. These somatic cilia are shorter and often more stiff than membranellar (mouth) cilia located in polykinetid bunches throughout the oral apparatus. Once Stentor has captured its prey, it corrals the prey into the oral pouch which then partially encloses. It is roughly around this point in which the feeding Stentor decides whether to consume the captured prey (although it is worth noting that food can still be rejected as late as the upper gullet). If the prey is rejected it will be ejected and passed down along the outside of the cell's body cilia towards the tail as to ensure it doesn't end up being accidentally consumed again. Long dead prey and non-organic material such as toxins or glass are more likely to be rejected, especially if the Stentor is otherwise well fed. Food is then passed into the gullet, an invaginated feeding apparatus lined with cilia and myonemes to aid in the passage of food items. The gullet's myonemes do a sort of peristalsis with rhythmic contractions forcing larger food items into an ectoplasmic food vacuole. Food vacuoles can also be formed inside the cytoplasm if prey escapes/ bursts its containing vesicle. Not all prey can be wholistically phagocytized, especially large prey like other Stentor. In these cases, the buccal cavity will expand to fit part of the prey (the tail end if it's eating another Stentor) and will subsequently close, cleaving part of the prey off like taking a chunk from a piece of meat. This smaller food chunk will then be ingested as outlined above. Cannibalism has been observed in multiple species of Stentor, with planktonic individuals being drawn in to the vortex of secured and feeding individuals. Nuclei and cell division Like other ciliates, the nuclei of Stentor are split into a macronucleus and micronucleus. The macronucleus is highly polyploid and any one fragment can contain many copies of the entire transcriptionally active genome. The micronucleus is much smaller and contains information necessary for the formation of the macronucleus and is essential for the process of conjugation. Macronuclear shape is diverse in Stentor, with many species having moniliform (bead like), variform (tube like), and condensed (resembling an enlarged single nucleus) macronuclei. Conjugation is relatively rare, with most organisms dividing asexually by fission. File:Mikrofoto.de-Stentor-1.jpg|Stentor polymorphus with algal symbionts File:Mikrofoto.de-Stentor-4.jpg|Stentor polymorphus with algal symbionts File:Dwa stentory.jpg|Stentors settled on water milfoil leaf File:Stentor coeruleus.png|Stentor coeruleus digesting Blepharisma sp. ==Ecology==

Although certain species of Stentor (S. multiformis) have been shown to live in marine and terrestrial habitats, the genus primarily lives within bodies of freshwater. However, many species are also found in more dystrophic or brackish freshwater environments. This is most frequent in the smaller and commonly planktonic species, which bear a stronger association with endosymbiotic algae. The blooming Stentor will cover the surface of a lake or pond giving it the coloured appearance of the species' cortical granules. The limiting nutrient that causes Stentor blooms is not commonly known, although certain cases have been studied and found to correlate with increased rainfall which can provide vitamin B12 producing bacteria or increased phosphorus. Although Stentor blooms have shown some evidence of damage to fish life and water purity, they are considerably less toxic than more typical algal blooms. == Practical importance ==

Although their large size and robust endoplasm make Stentor good subjects of study, their difficulty to culture and low sex frequency has kept them from being more widely studied. The strength of Stentor as a model for research lies with its remarkable regenerative abilities. Stentor can therefore provide insight into cellular specificity at multiple levels. The regenerative properties of Stentor can also be usefully applied to larger models of healing in order to understand the origin and cellular mechanisms behind healing in animals. ==Systematics==

Stentor was first described by the influential Genevan naturalist Abraham Trembley in 1744. Trembley initially misidentified the organism as a type of freshwater Hydra and in a letter addressed to the Royal Society described it as "Polypus", a "minute water animal". This initial description of the organism focused on its trumpet shape (with descriptions of both the buccal cavity and holdfast), circular like movement of its oral cilia, partial planktonic behaviour, and vortex feeding. The first use of the name "Stentor" was by German naturalist Lorenz Oken in 1815, although it referred to a much larger taxonomically unspecific group compared to today's genus. The first major organization of the genus was done by another German naturalist, Christian Gottfried Ehrenberg in 1831. He focused on characters not covered in the Foissner and Wölfl review, such as the characteristics of the oral pouch, orientation of stiff (somatic) cilia, and grafting experiments. Finally in 2006, Ying-Chun Gong constructed a clade using small subunit ribosomal rRNA from three Stentor species, indicating they are sister to the genus Blepharisma. ==Video gallery==