Planktonic Rotifers.
These are rotifers which swim freely in the open, usually surface, waters
of the pond or stream. They are strong swimmers, and some of the larger
ones are predaceous; most often preying on smaller rotifers.
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Asplanchna can be thought of as the killer whale of the rotifer world. It grows to around a millimetre in length, is a powerful swimmer, and feeds upon smaller
rotifers by projecting its jaws forward, seizing the prey, and hauling it
inside its highly transparent body in one rapid action.
The young develop to maturity within the parent's body, and are born
live. Two mature daughters, ready for birth, can be seen (one clearly) in
the lower body area of this specimen.
Darkfield, 100X. |
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Filinia is another common planktonic rotifer, smaller than Asplanchna, with two long lateral bristles which it uses to jump rapidly backwards when threatened.
This female specimen has a single egg attatched to the rear of its
abdomen.
Darkfield, 300X. |
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Synchaeta is a fast-swimming planktonic rotifer
characterised by an extremely thin transparent cuticle and, in addition to
the corona, two "ears" or auricles bearing groups of cirri which further
aid swimming. There are usually also four sensory bristles projecting
forwards. This female specimen (no males have been observed) has a
developing egg in its lower body.
Darkfield, 300X. |
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Testudinella is a fairly sensitive creature, and can spend a good deal of
its time contracted inside its very flattened tortoise-like lorica. Like
most rotifers, they feed and swim by means of their corona, and are not
predaceous. This one has two red eyes.
Darkfield, 300X. |
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