The water opossum (''Chironectes minimus''), also locally known as the yapok (), is a

marsupial Marsupials are any members of the mammalian infraclass Marsupialia. All extant marsupials are endemic to Australasia, Wallacea and the Americas. A distinctive characteristic common to most of these species is that the young are carried in ...

of the family Didelphidae.* It is the only living member of its

genus Genus ( plural genera ) is a taxonomic rank used in the biological classification of living and fossil organisms as well as viruses. In the hierarchy of biological classification, genus comes above species and below family. In binomial nom ...

, ''Chironectes''. This

semiaquatic In biology, semiaquatic can refer to various types of animals that spend part of their time in water, or plants that naturally grow partially submerged in water. Examples are given below. Semiaquatic animals Semi aquatic animals include: * Ve ...

creature is found in and near

freshwater Fresh water or freshwater is any naturally occurring liquid or frozen water containing low concentrations of dissolved salts and other total dissolved solids. Although the term specifically excludes seawater and brackish water, it does incl ...

streams and lakes from Mexico through Central and South America to Argentina and is the most aquatic living marsupial (the

lutrine opossum ''Lutreolina'' is a genus of opossum found in South America. Both extant species in this genus are known as lutrine opossums. They have an otter-like body plan and occasionally semiaquatic tendencies, hence the genus name ''Lutreolina'', which i ...

also has semiaquatic habits). It is also the only living marsupial in which both sexes have a pouch. The

thylacine The thylacine ( , or , also ) (''Thylacinus cynocephalus'') is an extinct carnivorous marsupial that was native to the Australian mainland and the islands of Tasmania and New Guinea. The last known live animal was captured in 1930 in Tasma ...

, commonly referred to as the Tasmanian tiger, also exhibited this trait, but it is now extinct. The water opossum lives in bankside burrows, emerging after dusk to swim and search for

fish Fish are Aquatic animal, aquatic, craniate, gill-bearing animals that lack Limb (anatomy), limbs with Digit (anatomy), digits. Included in this definition are the living hagfish, lampreys, and Chondrichthyes, cartilaginous and bony fish as we ...

crustacean Crustaceans (Crustacea, ) form a large, diverse arthropod taxon which includes such animals as decapoda, decapods, ostracoda, seed shrimp, branchiopoda, branchiopods, argulidae, fish lice, krill, remipedes, isopoda, isopods, barnacles, copepods, ...

s and other aquatic animals, which it eats on the bank.

Origin of the name

The local name for the water opossum, "yapok", probably comes from the name of the

Oyapok River The Oyapock or Oiapoque (; ; ) is a long river in South America that forms most of the border between the French overseas department of French Guiana and the Brazilian state of Amapá. Course The Oyapock runs through the Guianan moist for ...

French Guiana French Guiana ( or ; french: link=no, Guyane ; gcr, label= French Guianese Creole, Lagwiyann ) is an overseas department/region and single territorial collectivity of France on the northern Atlantic coast of South America in the Guianas ...

Physical appearance

The water opossum is a small opossum, 27-32.5 cm long, with a 36–40 cm long tail. The fur is in a marbled grey and black pattern, while the muzzle, eyestripe, and crown are all black. A light band runs across the forehead anterior to the ears, which are rounded and naked. There are sensory facial bristles in tufts above each eye, as well as whiskers. The water opossum's tail, furred and black at the base, is yellow or white at its end. The hindfeet of the water opossum are webbed, while the forefeet ("hands") are not. The forefeet can be used to feel for and grab prey as the animal swims, propelled by its tail and webbed back feet.Fernandez, Fernando Antonio dos Santos, et al.
Natural history of the water opossum Chironectes minimus: a review
" Oecologia Australis 19.1 (2015). Unlike other didelphids, the water opossum does not have a

cloaca In animal anatomy, a cloaca ( ), plural cloacae ( or ), is the posterior orifice that serves as the only opening for the digestive, reproductive, and urinary tracts (if present) of many vertebrate animals. All amphibians, reptiles and birds, ...

.Nogueira, José Carlos, et al.
Morphology of the male genital system of Chironectes minimus and comparison to other didelphid marsupials.
Journal of mammalogy 85.5 (2004): 834-841. Schwimmbeutler-drawing

Aquatic adaptations

The water opossum has several adaptations for its watery lifestyle. It has short, dense fur, which is water-repellent. The broad hindfeet are webbed and are used for propulsion through water, moving with alternate strokes. They are symmetrical as well, which distributes force equally along both borders of the webbing; this increases the efficiency of the water opossum's movement through the water. The water opossum's long tail also aids in swimming. Being a marsupial and at the same time an aquatic animal, the water opossum has evolved a way to protect its young while swimming. A strong ring of muscle makes the pouch (which opens to the rear) watertight, so the young remain dry, even when the mother is totally immersed in water. The male also has a pouch (although not as watertight as the female's), where he places his genitalia before swimming. This is thought to prevent them from becoming entangled in aquatic vegetation and is probably helpful in streamlining the animal as well.

Reproduction

Water opossums mate in December and a litter of 1-5 young is born 12 to 14 days later in the nest. By 22 days the offspring are beginning to show some fur, and by 40 days or so their eyes are open, their bodies protruding from the mother's pouch. At 48 days of age, the young opossums detach from the nipples, but they still nurse and sleep with the mother.

Fossil record

The water opossum seems to have a history dating as far back as to the

Pliocene The Pliocene ( ; also Pleiocene) is the epoch in the geologic time scale that extends from 5.333 million to 2.58Holocene The Holocene ( ) is the current geological epoch. It began approximately 11,650 cal years Before Present (), after the Last Glacial Period, which concluded with the Holocene glacial retreat. The Holocene and the preceding Pleistocene togeth ...

subfossil fragments of ''Chironectes'' have been discovered in

São Paulo São Paulo (, ; Portuguese for ' Saint Paul') is the most populous city in Brazil, and is the capital of the state of São Paulo, the most populous and wealthiest Brazilian state, located in the country's Southeast Region. Listed by the GaW ...

, Brazil. Also, there are fossil specimens from the late

Pleistocene The Pleistocene ( , often referred to as the ''Ice age'') is the geological Epoch (geology), epoch that lasted from about 2,580,000 to 11,700 years ago, spanning the Earth's most recent period of repeated glaciations. Before a change was fina ...

-Recent cave deposits in

Minas Gerais Minas Gerais () is a state in Southeastern Brazil. It ranks as the second most populous, the third by gross domestic product (GDP), and the fourth largest by area in the country. The state's capital and largest city, Belo Horizonte (literall ...

, Brazil, as well as from the late

Pliocene The Pliocene ( ; also Pleiocene) is the epoch in the geologic time scale that extends from 5.333 million to 2.58Entre Ríos Province Entre Ríos (, "Between Rivers") is a central province of Argentina, located in the Mesopotamia region. It borders the provinces of Buenos Aires (south), Corrientes (north) and Santa Fe (west), and Uruguay in the east. Its capital is Paraná ...

, Argentina.

Subspecies

*''Chironectes minimus argyrodytes'' *''Chironectes minimus langsdorffi'' *''Chironectes minimus minimus'' *''Chironectes minimus panamensis''

References

Footnotes

Bibliography

* *

External links

*
Oxford University Press, Journal of Mammalogy, Volume 90, Issue 1, 18 February 2009, Pages 93–103
* {{Taxonbar, from=Q660423 Opossums Aquatic mammals Marsupials of North America Marsupials of Central America Marsupials of South America Mammals of Argentina Mammals of Bolivia Mammals of Brazil Mammals of Colombia Mammals of Ecuador Mammals of French Guiana Mammals of Guyana Mammals of Mexico Mammals of Paraguay Mammals of Peru Mammals of Suriname Mammals of Venezuela Mammals of Trinidad and Tobago Mammals of the Caribbean Mammals described in 1780 Taxa named by Eberhard August Wilhelm von Zimmermann