The marine iguana (Amblyrhynchus cristatus) is an iguana found only on the Galápagos Islands that has the ability, unique among modern lizards, to forage in the sea, making it a marine reptile. The iguana can dive over 9 m (30 ft) into the water. It has spread to all the islands in the archipelago, and is sometimes called the Galápagos marine iguana. It mainly lives on the rocky Galápagos shore to warm from the comparably cold water, but can also be spotted in marshes and mangrove beaches.

On his visit to the islands, despite making extensive observations on the creatures, Charles Darwinwas revolted by the animals’ appearance, writing:

The black Lava rocks on the beach are frequented by large (2–3 ft [60–90 cm]), disgusting clumsy Lizards. They are as black as the porous rocks over which they crawl & seek their prey from the Sea. I call them ‘imps of darkness’. They assuredly well become the land they inhabit.^[3]

Marine iguanas are medium-sized lizards (200–340 mm, adult snout–vent length) and are unique as they are marine reptiles due to their foraging on inter- and subtidal algae only. These iguanas forage exclusively in the cold sea, which leads them to behavioral adaptations for thermoregulation.^[4]

Amblyrhynchus cristatus is not always black; the young have a lighter coloured dorsal stripe, and some adult specimens are grey, and adult males vary in colour with the season. Dark tones allow the lizards to rapidly absorb heat to minimize the period of lethargy after emerging from the water. The marine iguana lacks agility on land but is a graceful swimmer. Its laterally flattened tail and spiky dorsal fin aid in propulsion, while its long, sharp claws allow it to hold onto rocks in strong currents.^[5]

(From Wikipedia, April 2015)