Fig. (7) Specimen burrowed into coarse-grained (A-B) or layered (C-D) carbonate sand. A) The initial shape of the burrow formed in coarse-grained sand is a lop-sided U. B) Later, the specimen’s body contracted into a more symmetrical U shape. C) When encountering interbedded medium- and coarse-grained sand, the holothurian penetrated the medium-grained surface layer but did not fully penetrate the underlying coarse-grained layer. Medium-grained sand is transported downward by the burrowing animal. D) When disturbed at the surface, the specimen pushes downward through the coarse-grained layer. The dashed line outlines the burrow.