Sessile Rotifers.
There are two pages of sessile rotifers including this one.
This page shows a variety of sessile rotifers, and page 2 is a detailed look at the rotifer Floscularia and its "brick-making" activities.
Sessile rotifers are those which spend the main part of their lives
attatched to the stems of water plants, submerged tree rootlets, filaments of algae etc. and live by capturing the algae and other food organisms bought to them by a combination of their own feeding activities and the currents in the pond or stream in which they live. They are only free-swimming when newly
hatched and in search of a place to settle, or when conditions become
adverse and they are obliged to find another home.
Almost all sessile rotifers build some kind of protective tube in which
to live. Some tubes are merely the accumulation of mucous secretion which
is compacted around the foot by their feeding current, and others are
smooth regular tubes built by the rotifer from carefully deposited
individual pellets of compacted debris.
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This rotifer of the genus Collotheca lives in a
transparent gelatinous case and has a funnel-shaped mouth surrounded by a
corona with extremely long cilia which are also extremely fine and
actually extend to the edge of the picture. Prey organisms become
entangled in the cilia and are drawn into the mouth by their contraction.
These creatures are a very impressive sight, and much better viewed live
under a microscope than as a graphic on a monitor.
Darkfield, 200X. |
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Here a Ptygura rotifer is seen feeding; its circular corona extended from
a mucilaginous case which has become coloured a characteristic red-brown
by absorption of iron from the water.
Darkfield, 400X. |
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Same Ptygura as above, but with corona contracted. The yellow oval object
is the motile alga Trachelomonas whose collision with the rotifer has just
caused the rotifer's contraction. One of two dorsal sensory antennae is seen in the plane of focus.
Darkfield, 400X. |
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An extended Ptygura in a setting of filamentous algae, decaying matter and other stuff impossible to identify with any degree of certainty.
Darkfield,200X. |
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This Ptygura is extended from its newly formed and almost invisible case
attatched to a filament of Spirogyra. A second filament in the background
gives some idea of the size of the creature.
Darkfield, 400X. |
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The sessile rotifer Floscularia builds itself a gently tapering conical
case from round pellets of compacted debris which are produced in a
special organ on the creature's dorsal side.
As each pellet is completed, the rotifer bends over to cement it on the advancing edge of the case, and straightens once more to continue with the compacting of the next pellet. Fascinating to watch if you are lucky enough to find one.
Here is a diagram of Floscularia.
Darkfield, 100X. |
