The reniculate kidney is a multilobed

kidney In humans, the kidneys are two reddish-brown bean-shaped blood-filtering organ (anatomy), organs that are a multilobar, multipapillary form of mammalian kidneys, usually without signs of external lobulation. They are located on the left and rig ...

found in marine and

aquatic mammal Aquatic mammals and semiaquatic mammals are a diverse group of mammals that dwell partly or entirely in body of water, bodies of water. They include the various ''marine mammals'' who dwell in oceans, as well as various freshwater species, such a ...

s such as

pinniped Pinnipeds (pronounced ), commonly known as seals, are a widely range (biology), distributed and diverse clade of carnivorous, fin-footed, semiaquatic, mostly marine mammals. They comprise the extant taxon, extant families Odobenidae (whose onl ...

s ( seals,

sea lion Sea lions are pinnipeds characterized by external ear flaps, long foreflippers, the ability to walk on all fours, short and thick hair, and a big chest and belly. Together with the fur seals, they make up the family Otariidae, eared seals. ...

s and

walrus The walrus (''Odobenus rosmarus'') is a large pinniped marine mammal with discontinuous distribution about the North Pole in the Arctic Ocean and subarctic seas of the Northern Hemisphere. It is the only extant species in the family Odobeni ...

es) and

cetacean Cetacea (; , ) is an infraorder of aquatic mammals belonging to the order Artiodactyla that includes whales, dolphins and porpoises. Key characteristics are their fully aquatic lifestyle, streamlined body shape, often large size and exclusively c ...

s (

dolphin A dolphin is an aquatic mammal in the cetacean clade Odontoceti (toothed whale). Dolphins belong to the families Delphinidae (the oceanic dolphins), Platanistidae (the Indian river dolphins), Iniidae (the New World river dolphins), Pontopori ...

s and

whale Whales are a widely distributed and diverse group of fully Aquatic animal, aquatic placental mammal, placental marine mammals. As an informal and Colloquialism, colloquial grouping, they correspond to large members of the infraorder Cetacea ...

s) but absent in terrestrial mammals except

bear Bears are carnivoran mammals of the family (biology), family Ursidae (). They are classified as caniforms, or doglike carnivorans. Although only eight species of bears are extant, they are widespread, appearing in a wide variety of habitats ...

s. Kidneys of this morphology have increased surface area for removing toxins from the body more efficiently than a non-lobed kidney. The reniculate structure in cetaceans and pinnipeds does not result in a greater concentrating ability. While many marine mammals can concentrate their urine beyond the concentration of sea water, only

sirenians The Sirenia (), commonly referred to as sea cows or sirenians, are an order (biology), order of fully aquatic, herbivorous mammals that inhabit swamps, rivers, estuaries, marine wetlands, and coastal marine waters. The extant Sirenia comprise tw ...

and

otters Otters are carnivorous mammals in the Rank (zoology), subfamily Lutrinae. The 13 extant otter species are all semiaquatic, aquatic animal, aquatic, or Marine ecology, marine. Lutrinae is a branch of the Mustelidae Family (biology), family, whi ...

can reach levels of Na⁺ and Cl⁻ concentrations similar to sea water, making it possible for them to consume salt water without losing fresh water. However, pinnipeds and cetaceans typically regulate their water balance by metabolism and only drink sea water occasionally to maintain salt balance. In contrast, sea otters and manatees often drink sea and fresh water.

References

{{reflist Mammal anatomy Urinary system