The Web-footed Tenrec (Microgale mergulus), also known as the aquatic tenrec or otter shrew , is the only known semiaquatic Malagasy tenrec (the related African otter shrews have similar habits), and is found in eastern Madagascar, especially in and around Ranomafana National Park. It grows to between 25 and 39 cm, and was once thought to be extinct. It feeds on crabs, water insects, and crayfish. It weighs between 40 and 60 grams, and the population is considered vulnerable. It was formerly placed in the monotypic genus Limnogale, but has been moved to Microgale based on molecular data showing it to be deeply nested within the latter.
It is strictly nocturnal, spending the day in stream side burrows, only emerging at night to hunt. Nocturnal movements appear to be restricted to waterways but include movements away from burrows and diving. Radio collar tracking has shown that some individuals are known to utilize stream channels as much as 1160 meters in length, while others may only patrol 500 meters. In one night a web-footed tenrec may travel 1550 meters along channels in search of food.
The web-footed tenrec is only known to inhabit stream habitats in eastern Madagascar. Lypotyphlan is a term which has been used to group small, insectivorous mammals. While this term is no longer used in phylogenetics, it can still be used to accurately signify the diet of the web-footed tenrec. The bulk of its diet consists of aquatic insects and larvae, with crustaceans like crayfish and small fish making up the rest. The larvae of insects in the orders Ephemeroptera, Odonata and Trichoptera being favorites. Diets of individuals inhabiting zero-canopy steams appears to be the same as those living in forested streams.