Stentor

Stentor is a genus of filter-feeding ciliates. They are usually horn-shaped, and reaching lengths of 2 millimeters, they are among the biggest known unicellular organisms.

Stentor
Stentor roeselii
Scientific classification
Unrecognized taxon (fix):	Stentor
Species
Stentor amethystinus Stentor araucanus Stentor baicalius (syn. Stentor pygmaeus) Stentor barretti Stentor caudatus Stentor coeruleus Stentor cornutus Stentor elegans Stentor fuliginosus Stentor igneus Stentor introversus Stentor katashimai Stentor loricatus Stentor magnus Stentor muelleri (syn. Stentor felici) Stentor multiformis (syn. Stentor gallinulus, =Stentor nanus) Stentor multimicronucleatus Stentor niger Stentor polymorphus (syn. Stentor pediculatus) Stentor pyriformis Stentor roeselii

They are a type of protist ciliate in the heterotrich class. The old-fashioned name for them was trumpet animalcules.

The body is horn-shaped, with a ring of prominent cilia around the anterior "bell" that sweeps in food and helps swimming. Some reach several millimeters in length, making them among the largest single celled organisms. As in many freshwater protozoans, Stentor has a contractile vacuole. Because the concentration of salt inside the cell and in the surrounding freshwater is different, Stentor must store water that enters it by osmosis and then discharge it from the vacuole. They can regenerate, and small fragments can grow into full organisms. Each cell has one (often elongated) macronucleus and several micronuclei. Having two types of nuclei is charcteristic of ciliates.