While finning around a sand and algae bottom not far from where the Rocio del Mar swings at anchor in the Gulf of California, we come face to face with a monster living in a hole. We’ve seen the silver-dollar-size burrows before in Caribbean sea-grass meadows, but because they appeared uninhabited, we passed them by.

Today is different: From several feet away, we catch a glimpse of the hairy forebody and massive claws of a ferocious-looking crustacean. Anything that looks that menacing must be a meat eater, we assume, so on the next dive we return with a shrimp from the galley and place it by the burrow. Nothing.

Later, while watching from a distance, we see a claw shoot up and snag a piece of floating sargassum weed. So Anna pinches off a branch and places it over the burrow; the offering vanishes, and we begin luring our quarry into view with algae. No matter how much we proffer, the little glutton never tires of the largesse.

Later we learn that our minimonster is a lobster shrimp, a poorly-studied group with members that store vast amounts of vegetation in chambers of their U-shaped burrows. Teir cupboards not only stockpile food, but also help retain significant amounts of nutrients in the habitat.

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