Strange-looking sea monsters dart past as I snorkel close to the beach. I imagine I've somehow gatecrashed a chilling scene in a Japanese horror movie. But, fortunately, these weird dinosaur-like creatures are totally harmless.
Marine iguanas are found only in the Galapagos Islands, an all-year tourist destination for viewing some of the world's most unusual creatures.
Without realising it, marine iguanas help make this offshore Ecuadoran territory a major location for seeing strictly protected wildlife.
The islands are best known for giant tortoises, which have become their symbol. In fact, tortoises gave the islands their name - "galapago" means saddle in Spanish after the animals with a shell that resembles a saddle.
Marine iguanas, meanwhile, are strong swimmers and divide their time between the sea (where they eat ocean algae) and the land (where they bask on rocks and beaches). Because they blend so well against their backgrounds, visitors are warned not to step on them.
Male marine iguanas, growing to 1.5m and far outnumbered by their harems, often appear asleep. But they dare not relax.