Stentor is a heterotrophic ciliate protozoa also known as, "trumpet animalcule", because they look like a miniature trumpet. The organism was name after the Greek herald known for his loud voice during the Trojan War.
There are many interesting facts about this organism. Stentors are bigger than many multicellular organisms found in freshwater, such as rotifers and water fleas. Sometimes, they reach to 2 millimeters (0.08 inch), scientists can find this creature so easily from almost everywhere. Stentor eats the organisms that are smaller than it. Stentor is the class Spirotrichea and in the phylum Ciliophora. This creature is the easiest for microscopist to study. Because of its size. Stentor is unique from other single cell organisms in feeding, excretion, digestion, respiration and reproduction. And it eats food with cilia around the anterior "bell", which sweeps the food in and helps the creature to swim. Stentor has to store water that enters by osmosis and get it back out from vacuole.
Stentor feeds on bacteria and other small creatures using a crown of fused cilia (hairlike structures). But it uses cilia to locomote when something or anything disturbs it. 
Stentor can be found in ciliate measuring from 500-2000 microns, and Stentor polymorphus is 500-1500um long. Stentor coeruleus is really big trumpet shaped, and its macronucleus's color is blue and blue-green and looks like bead, the reason that it has blue color is because of stentorin. Some stentors can be in different color, and some of them can grow to millimeters in length that makes it the largest single celled organisms. Stentor is like a stalked ciliate. A main identification feature is the existence of cilia which looks like a hair-like projections, and appears on the sides of the organism.
Their shape changes into bell-shape body when they attach to the bottom of a sea or lake. They can swim freely, and change into pear shaped when they swim. It's a very good swimmer because of the cilia. This organism has incredible regenerative powers. The very small amount of an adult Stentor can grow back to a complete organism. Some of Stentors are also very colorful, they can be green, blue, and even amethyst. There are two fiber systems that can be found in the cell cortex, and they control contraction and extension. 
Stentor uses micronucleus for reproduction. When two Stentors move and meet each other, they may seperate each other or mate with each other. Stentors reproduce asexually through binary fission. But They can also reproduce sexually via conjugation. Before the division the macronuclear nodes turns into ovoid form. The division begins where the kinetosomes appears which is located between the peristome and the holdfast, and that part is called region of stripe contrast. Just like ciliates, Stentor sustains sex through the process of conjugation. Micronuclei is passed on when they reproduce, and the macronuclei are made by the micronuclei. The population of Stentor goes high in autumn, because the leaves from the plants fall into the pond, and then, the population of bacteria increases in the pond to feed on the decaying vegetation. This causes an increase of bacteria population. So Stentor, starts feeding on bacteria. They eat, the population grows up. But in winter the population decreases as the bacteria's population decreases.
Stentor usually inhabit freshwater lakes and streams and prefer to inhabit dim and dark areas. To get away from light, Stentor coeruleus changes the direction of its ciliary beat to reverse the direction. However, there are some Stentors that like to inhabit in wastewater, they are even found in waste water treatment processes. But there are some exception. If bacteria populations and dissolved oxygen concentrations of the treatment process are higher than usual, Stentors are found in low numbers. They seem to prefer to inhabit in a stable environment like wastewater and a healthy biomass. They are usually attached to algae and other detritus. And they eat bacteria and algae while they are attached to it. 
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- Stentor Unknown. Environmental Leverage Inc.
- Stentor Unknown. Microbus.
- Micscape Article Dave Walker.Microscopy UK