They may have been dubbed the "imps of darkness" by a certain bearded naturalist, but there is nothing quite like watching marine iguanas chow down to bring some cheer to your hump day! 

This awesome clip was filmed in the Galápagos, of course – the only place in the world where you'll find these aquatic lizards. At first glance, marine iguanas look much like their land-loving cousins, but strong claws, flattened tails and thick hind legs make them skilled swimmers. In fact, these Godzilla-like grazers will dive up to 25 metres on a single breath in search of their favourite salty snack: seaweed. 

You'll notice this lizard has a salt-encrusted head, and that too is the result of an all-seaweed diet. Snacking on high-sodium foods can be hard on the system, so special glands connected to the iguanas' nostrils allow them to expel excess sea salt, an ingenious design that can also be seen in many "tube-nosed" sea birds. The discharge happens at the surface when the iguanas exit the water to bask, and as you can imagine, salt-sneezing is quite the spectacle:

And that's not the only adaptation that sets marine iguanas apart. Back in 2000, researchers found that when food is scarce, the animals not only get thinner, but they also get shorter. The iguanas can switch between periods of growth and shrinkage throughout their lifetimes, and they're the only adult vertebrates known to do so.

"The scale of the shrinkage (up to 20% of body length) means that it cannot simply be explained by decreases in cartilage and connective tissue, which together make up only 10% of total body length,” researchers write. When food becomes plentiful again, the lizards regain their length. Scientists believe this adaptation helps the sea-going reptiles handle El Niño years on the island. 

The Galápagos may be an equatorial paradise, but the Humboldt Current sweeping through the region means the waters around the island chain stay relatively cool. When an iguana dives in, the clock is always ticking: staying beneath the surface too long could lower its body temperature to dangerous levels. Because of this, only the largest marine iguanas take the plunge. Smaller animals lose heat too readily, and prefer to graze on algae near the surface. 

And where did these strange creatures come from? The best guess is that land-dwelling iguanas from South America drifted out to sea millions of years ago, hitching a ride on logs or other debris. These drifters eventually washed ashore on the archipelago, and today's marine iguanas rose up from those ancient ancestors.

Today, each island in the Galápagos hosts iguanas of a unique size and colour, ranging from the all-black "imps" that Darwin detested, to a vibrant blend of red, blue, grey and green. 

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Top header image: Max Westby/Flickr