Limnogale mergulus
aquatic tenrec

L. mergulus is found only in eastern Madagascar's high altitude stream and marsh regions.

L. mergulus is found only in regions of fast-flowing streams on steep sloping cliffs and highlands. These regions may either be forested or not. Currently, there are only ten known sites that have supported this species; however, it may have disappeared from two due to habitat destruction.

The fur is short, dense, and soft, with a texture similar to that of an otter. L. mergulus is brown in color, but also has hairs of red and black appearance interspersed. The underbelly is pale yellowish gray. The skin of this species is black on the dorsal surface and gray on the ventral surface. The head is small and broad compared to the body, and it has a flattened appearance. The slightly blunt muzzle is covered in short vibrissae that are a very effective sense organ. The eyes and ears are also small. In fact, the fur nearly covers the ears, perhaps as an aquatic adaptation. L. mergulus also has webbed toes (thus its common name) and a thick powerful tail to aid in swimming. It has recently been observed that the hind feet are the primary mode of propulsion with the tail acting as a rudder. The tail is approximately 61-119 mm long, accounting for almost half the length of the animal, and has a square shape. The fringed forefeet are used mostly to hold captured prey for consumption. L. mergulus has a true cloaca and it has also been noted that the testes of the male never descend from the body into a scrotum, instead remaining in the abdominal cavity. The dental formula is 3/3,1/1,3/3,3/3.

While there has been little research, breeding is thought to take place in December and January, resulting in an approximate litter size of three. Females possess six mammae. The gestation period is unknown.

L. mergulus is strictly nocturnal and does not utilize the predictable foraging and movement patterns of other aquatic mammals, such as desmans. Time of activity and level of activity, as well as extent and direction of movement, are unpredictable. A possible explanation of this unpredictability is that this species has no need to defend a territory as a result of low species population density. While the movement of this species is unpredictable, it is always nocturnal and limits itself to certain stream networks. These networks are their only means of dispersal. The distance traveled on any night varies widely from individual to individual and from night to night, averaging 800-1000m, but depending on the length of the stream channel. Movement may be both upstream and downstream and also follows no predictable pattern. During the day, members of this species sleep in streamside burrows. Each individual has a permanent burrow that it returns to after each night of foraging. Excavation of one burrow showed that it was horizontally dug into the bank of a steam above the water line. Carpeted with sticks and grass, the burrow was approximately 17cm deep and 10cm in diameter. L .mergulus has been observed to lick and groom.

L. mergulus is a stictly nocturnal, aquatic forager, using its vibrissae and sweeping motions of the head to search the stream bed for prey. After prey are captured using the mouth, they are brought to the surface, where L. mergulus rolls on its back and kicks the prey into submission using its hind feet. Prey are then brought to shore or to a rock, grasped with the forefeet and consumed in bites. Insects, both larval and adult, are the dominate prey; however, diet varies by stream. They also eat larval anurans (small frogs), and crayfish.

L. mergulus may be important in the control of certain insect populations.

L. mergulus feeds on insect larvae that may act as pests to humans.

The endangered status of L.mergulus is as a result of loss of habitat due to human expansion. It is thought that by protecting new and existing sites, we can protect the food source of this species, thereby protecting the species itself.