Radial Expansion Favors the Burrowing Behavior of Urechis unicinctus

Figure 1

The burrowing behavior of Urechis unicinctus under the sand. (a) Urechis unicinctus can advance in sands by peristaltic motion. (b) The radial expansion and the advancement of the head are carried out alternately. (c) The trajectory of one sand particle near the head shows that the radial expansion can make the sands flow.

(a)

(b)

(c)