About Varanus mertensi Glauert, 1951
Mertens' water monitor (Varanus mertensi) reaches a total length including the tail of about 2.0 meters (6.6 feet). Its dorsal side is dark brown to black, marked with numerous cream to yellow spots. Its underparts are paler, ranging from white to yellowish, with grey mottling on the throat and blue-grey bars across the chest. Its tail is strongly laterally compressed, has a high median dorsal keel, and is approximately 1.5 times the length of the head and body combined. Among all monitor species, including the water monitors of the subgenus Soterosaurus, Mertens' water monitor is the most morphologically adapted to an aquatic lifestyle. It can close its upward-facing nostrils to seal them when underwater. This species is able to swallow prey underwater, an ability that has only been reported in one other monitor species: the Borneo earless monitor (Lanthanotus borneensis). It is also the only monitor species that has been reported to use its sense of smell to locate and capture prey while underwater. Mertens' water monitor inhabits coastal and inland waters across most of northern Australia. Its range extends from the Kimberley region of Western Australia, across the Top End of the Northern Territory and the Gulf Country, to the western side of Cape York Peninsula in Far North Queensland.
