Fig. 8.

The foot of a crawling gastropod is characterized by three distinct regions (waves, interwaves and the rim), as shown in this velocity contour map of a portion of the ventral surface of a banana slug (∼20% of the length of the animal is shown). The velocity was measured along the direction of motion of the slug and in the laboratory reference frame (zero velocity means that the animal is stationary with respect to the substrate). The waves (red d-shaped regions), interwaves (blue d-shaped regions) and rim (pale green/yellow regions flanking the waves and interwaves) can be distinguished by their distinct velocity magnitudes. Notice that the velocity dropped to zero behind each wave and increased abruptly upon reaching the wave region. The blue patch of low-velocity regions on the lower right portion of the first wave from the right was caused by hardened mucus left by the slug during previous trials.