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What will happen when the food first comes from the left (twice) and then suddenly from the right?


In these three clips a female Eucalanus pileatus is viewed head on. The food, algae, are introduced to the feeding current on left side. The animal modifies the feeding current to attract the water from the left. And when algae are within the feeding current, they are captured with an ease.


The first clip (on the right) shows the capture when the mouthparts responsible for the food handling are not in motion. Note the precise food handling when the alga appears.
This second clip shows the food handling when the mouthparts are already busy with the first alga. Note that there is no difference in motion when compared to the motion of the clip above.


The animal has the ability to create the feeding current with some of the mouthparts (see the Generation of the Feeding Current) and while generating the current also stirs food particles close to the capture area, and to handle captured particles with the mouthparts closer to the mouth opening. For a good example, see the Handling of a glass particle.
Now, the question arises, what will happen if there is an alga on the right? If the animal does not react to that alga, the alga will by-pass the animal, just like the dye stream does. Good food may be lost!


In the third clip an alga approaches from the right. The animal redirects the feeding current in order to get the alga passing through the capture area. And captures the alga.


We can count the frames between the change in the feeding current and the arrival of the alga and then can estimate that the animal got aware of the alga on the right side when the alga was 2 animal body lengths away from the capture area.
These observation lead to Koehl & Strickler 1981
Clips from 16 mm movies at 500 frames per second
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