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Ron Neumeyer

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Bdelloid Rotifers - Rotifers in Aquaculture

rotifer1.jpg (32120 bytes)
Some of the cilia forming the "wheel organ" of the head are visible, frozen by the electronic flash used to take this picture. These organs, which look a bit like rotating wheels, appear only a few genera but have given the whole class its name. These cilia stroke forward and back at very high speed creating a whirlpool that draws food material toward the mouth.  (darkfield illumination)
rotifer6.jpg (14105 bytes)
A Philodina rotifer "grazing" on a group of spherical flagellates of the genus Haematococcus. The cartenoid pigments inside the flagellate created the orange-red tinge in the gut of the Philodina in the proceeding picture (both were present on the same slide). (darkfield illumination)
rotifer3.jpg (55828 bytes)
"trapper" rotifer
These animals snare their prey, rather than draw them in by means of a whirlpool. In these sessile rotifers the anterior part is markedly transformed, for the wheel organ, the mouth and the gullet have been combined into a gaping funnel whose margin may be smooth, or equipped with lobes which bear long stiff cilia (as in this case). (darkfield illumination)
rotifer4.jpg (51235 bytes)
This particular rotifer is a sessile adult that has secreted a gelatinous envelope, or "case". There is a foot, which is attached to a strand of filamentous algae by means of a secreted gelatinous "glue". (phase contrast illumination)
rotifer5.jpg (16187 bytes)
Several different types of Rotifera. The large one attached to debris in the upper left has a very pronounced wheel organ. However, a few of the others, which are highly motile, have a less pronounced organ as they rely more on encountering food while moving, or browsing the surface of particles, then on setting up whirlpools. (The wheel organ can also used for propelling the animal through the water, or along surfaces.) (darkfield illumination)
rotifer2.jpg (9186 bytes)
bdelloid rotifer
A bdelloid rotifer with a pronounced wheel organ. It is difficult to identify because it has telescoped its body. The series of  rings, which make the body appear to be segmented, are in reality zones of folding of the gelatinous cuticle. There is no true segmentation in rotifers. (darkfield illumination)
rotifer11.jpg (52196 bytes)
bdelloid rotifer
This image illustrates the extreme flexibility of the gelatinous cuticle.  Folds can be seen running in a posterior-anterior direction. When viewed live, the position and shape of the folds change continuously as the animal moves around. If one looks closely at the head region (top left) a tiny pair of pigmented "eyespots" can be seen. These resided on the lateral surface of the brain, but their function is questionable.
rotifer13.jpg (14532 bytes) A rotifer with a rigid cuticle forming an ellipsoid case in which the body resides. This rotifer has a short foot, which exhibits the pseudo-segmentation of the cuticle. The foot in this animal services to push it along as it searches for food. (darkfield illumination)