Fredericella sultana through a microscope
Fredericella sultana has a typical round polyp that extends from the top of the zooid. The zooid wall is covered in diverse material, making it difficult to see through it to the internal organs. In this picture the cover is limited, making some of the internal organs visible through the zooid wall.
The next picture shows a detail of the previous one: the polyp base.
The upper side of the zooid opening clearly shows that the brownish cover is on the zooid wall and not in it.
The key reason the show this cutout is that it illustrates that the base of the tentacles are covered in a thin layer of tissue. It could be that this is for protection. It could also be that it has a role in food capture, making it more difficult for food to escape through the tentacles. Video 2 (see below) makes this point more relevant.
The next picture shows another zooid. To me it illustrates the incredible control the zooid has over the polyp and its individual tentacles. The picture shows how the tip of one tentacle can be curled up. Other pictures of the same polyp show that this is a transient effect and not a damaged polyp.
This picture shows the internal organs of a zooid. Two zooids have grown closely together (i think) and one has not extended its polyp. The gut is clearly visible. On the under side of the gut the retractor muscle can be seen that retracts the polyp into the zooid cavity.
The following series of pictures show the extension of a polyp. Pay attention to the flexibility of the zooid area around the aperture. It changes size and direction while the polyp extends. The later pictures show that tentacles can be moved individually and in various places.
The videos below are in WMV format and require a compatible player, such as windows media player, to view.
Each video is 30 to 60 seconds and 1.5 MB in size. Playing across a slow internet link may take a lot of time.
(click on the photo to start the video)
The first video (2,9 MB) shows a Fredericella sultana polyp during normal activities.
The polyp moves and the tentacles move.
The particles that move across the screen move mainly in reaction to water movement caused by moving the petri-dish that holds the colony.
This video (2,8 MB) shows what happens if a food particle must be captured. Fascinating movement of all tentacles of the polyp.
The next video (2,9 MB) shows polyp movement. The polyp is clearly busy changing its angle in an attempt to capture more food elsewhere in its environment.
The following video (4,3 MB) shows the internal organs of a Fredericella articulata zooid.
The gut movements can be clearly seen and also a particle that is swallowed.
The last video (5,7 MB) shows how a Fredericella articulata polyp extends.
F. sultana does that rapidly causing me to miss the initial part.