Stentors - some of the largest single celled organisms in the world

Stentors are trumpet shaped single celled organisms found in freshwater habitats like pods and streams. Due to their shape they are more commonly known as trumpet animalcules. Stentors are some of the largest single celled organism in the world, with the largest species reaching a size of up to two millimeters, and it is therefore possible to spot them in a water sample without a microscope. Stentors are ciliates, which mean that they move and feed with tiny hair-like projections called cilia. They have a large number of these cilia surrounding the mouth which creates a current of water carrying food particles for ingestion. In the opposite end they have a foot which is they use to adhere to a substrate.

Observe the classic trumpet shaped appearance and the clearly visible cilia surrounding the mouth.

Some species, like the S. Polymophus in the image, have a symbiotic relationship with the alga chlorella. When the stentor ingests a chlorella, the alga lives on and produces nutrients via photosynthesis which the stentor then absorbs. So, in return for the nutrients, the stentor provides protection for the algae, as well as waste products which the algae feed on. This symbiosis gives this stentor species its green color, but other species are brown, blue, transparent and even pink.

Stentors have the ability to contract rapidly when startled as a defence mechanism. Which gives them a round/oval appearance. Inside a stentor are some well defined organelles, like contractile vacuoles, their nucleus and food vacuoles. The nucleus in S. Polymorphus looks like a transparent string of beads.

Observe the clearly visible nucleus resembling a string of beads.

These organisms have incredible regenerative abilities and if the stentor gets torn apart, each segment will be able to regrow. In fact, fragments as small as 1/64 of the body is able to successfully grow back to a normally sized and shaped cell.

A video of Stentor Polymorphus seen with oblique and darkfield illumination, 10x and 20x objectives.