Underwater Cornucopias

What am I looking at?

This image shows three stentors (Stentor coeruleus) in a free-swimming form. The animal’s tapered body is called a cortex. Its flat front, the peristome (1), is surrounded by oral cilia (2) that sweep food particles into its oral pouch (3), which is located near an indentation at the edge of the peristome. The colored spheres inside the cortex are the nodes of its segmented macronucleus (4).

Stentors are known to utilize a single protein, tubulin, to produce structures like long cables (5), which give shape to their bodies; short cilia for locomotion (6) – these are visible particularly clearly in the specimen in the middle; and longer cilia for feeding (2). The cilia in this image were visualized using an antibody against acetylated tubulin and are shown in hues ranging from white to orange.

Biology in the background

The horn-like form that a stentor assumes when it’s fully extended gave rise to the name of its genus, as the shape is evocative of Stentor, the Greek herald in Homer’s Iliad. The members of the Stentor genus are protozoans – single-celled aquatic organisms covered in hair-like organelles called cilia; in fact, another name for such protozoans is ciliates. Although perhaps not as iconic a protozoan as a paramecium, a stentor is readily recognizable by even an amateur biologist thanks to its conical body.

A Stentor coeruleus is a so-called filter-feeder, sweeping up and ingesting decaying organic matter, particles, bacteria, other ciliates, and even multicellular microfauna like rotifers. Stentors form a symbiotic relationship with algae that gives them a greenish-blue color. The algae feed on stentors’ waste products while sharing some nutrients with their host.  

Stentors reproduce asexually by splitting themselves into two. In addition, they can regenerate parts of themselves if they’re damaged. If a cell is cut into several pieces, for example, each piece has the potential to grow into an entirely new organism. Like other ciliates, they have an elongated nucleus, but in this species it consists of linked nodes, giving it the appearance of beads on a string. They also have a tiny micronucleus containing a copy of their entire genome; though it’s transcriptionally inactive, it is used in sexual reproduction.

Stentors are among the larger single-celled animals in the world; they can grow up to 2 millimeters long when they’re fully extended, or roughly 10 times smaller than the width of a human thumbnail. The stentors in this image are about 300 micrometers long, or roughly four times the width of a human hair.

Technique

These images were created using confocal microscopy.