Strings of periwinkles, tiny rock-dwelling gastropods, take advantage of low tide to make a crossing.
Here, they glide, en masse, from the tip of rock in the lower left, to new grounds on the rock stretching across the top. Pioneers mark the crossing with mucus. Less adventurous gastropodestrians follow along, single file.
But not all the winkles are on the move. Nearby, some stay put, feasting.
