A tiny crab, not more than 4 inches/10 cm across, scuttling across Playa Langosta. Mrs. C found a bunch more on one of the lava rock formations jutting out of the water. They were wet and slippery, and I have a poor sense of balance (from creaky knees and trifocals?) so I decided to take her word for it.
Those are three tiny snails in front of the crab. I don't think it was interested in them as a snack. The crab found its way into a hole in the sand moments later. The bottom picture is a broad view of the area.