Before becoming full worms, Sandworms began their lives as sand plankton, then matured into the sandtrout form. In that phase the swam freely through the sand and sealed off all available water in the porous lower strata. Fremen/DE children played with sandtrout by placing them on their hands and amused watching them mold themselves to the shape; they would then shake the trout off and admire the "gloves" thus formed.