The type of escape response depends on the region of the crayfish that is stimulated but all forms require abdominal contractions. When a strong, unpleasant tactile stimulus is presented, such as a burst of water or the prod of a probe, a stereotyped behavior occurs in which the muscular tail and wide tail fan region of the telson are used like a paddle to propel the crustacean away from harm using a powerful abdominal flexions. The entire process occurs in a fraction of a second as movements are generated within two hundredths of a second (20 milliseconds) from the original trigger stimulus and the period of latency after a flexion is a hundredth of a second (10 milliseconds). Finally, the caridoid escape reflex requires that neurons be able to complete the arduous task of synchronizing the flexion of several abdominal segments. The speed, coordination, and decisiveness of the process seem to be the main attributes to its success. Like other decapod crustaceans, the crayfish possesses a hard, segmented exoskeleton that reflects muscular and neural segmentation. The anterior portion of the crayfish is the cephalothorax region. The region rostral to the cephalic grove, which separates the head and thorax region, is characterized by the presence of eyes, antennae and claws while the region caudal contains four pairs of walking legs. This is the crayfish's primary mode of locomotion. The abdominal section of the crayfish is divided into seven segments. These segments are flexibly interconnected, forming the tail. Normally, the tail is held in an extended position to aid in maneuvering and balancing. The first five segments are similar and the two terminal segments are modified into a tail fan, a region with high surface area that acts as the blade of a paddle in the escape response. This region contains the telson. The abdominal segments contain swimmerets, which aid in swimming. The anterior five segments of the crayfish house the massive flexor and extensor muscles. Six abdominal ganglia run down the entire length of the abdomen and communicate with one another through projections. The first five abdominal segments each have their own ganglion, that contains three roots with outward projections. The first has mixed sensory and motor nerves innervating swimmerets while the second has sensory and motor neurons that innervate the extensor muscles, while the third root contains only motor neuron projections that extend into the flexor muscles. The last segment contains the fusion of two ganglia.