Peristaltic Crawling in an Oligochaete


CONTROLLING THE ANIMATION:
Wait for the animation to load completely and play through once. To stop the animation, click on the "pause" button. To see the frame that precedes the paused frame, click on the "previous" button. To see the frame that follows the paused frame, click on the "next" button. To resume the animation, click on the "play" button.

PROCEDURE:
1)
As you observe the animation, identify the head end and prostomium. Pause the animation and identify segments that are in a state of shortening. Also identify segments that are in a state of elongation (= constriction).  Make a careful and detailed tracing of the entire image for later reference.
2) Resume the animation and note that areas of segment elongation and shortening are progressively moving, in a peristaltic-fashion.  In what direction do these waves move in relation to the head end of the worm - - forward or rearward?
3) Carefully study the worm's movements near the head end and describe how the worm anchors the segments near its head end during forward crawling?
4) Pause the animation and use a millimeter ruler to measure (to the nearest mm) the length and diameter of a segment that is fully elongated. (Do not use the first 2 segments). Next, make length and diameter measurements for this same segment when it is fully shortened.  Now, calculate and compare the volume of the segment (in cubic millimeters) when it is in a fully elongated state versus a fully shortened state. Would you expect the volumes to be about the same? If so, explain in relation to the concept of a "hydrostatic skeleton."
   [NOTE: For calculations, assume that segments remain uniformly cylindrical in shape and that the volume of a cylinder = pi x radius2 x length]
5) Consult references regarding the muscle organization of the worm's body wall.  What muscle layer contracts when segments are shortened? What muscle layer contracts when segments are elongated?
6) Explain how oligochaete worms might use this form of locomotion to make burrows in the soil or sediment where they live.

Click here to see non-interactive GIF animation 
Software for controlling interactive animations was developed by TOM DREWES