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

marsupial Marsupials are a diverse group of mammals belonging to the infraclass Marsupialia. They are natively found in Australasia, Wallacea, and the Americas. One of marsupials' unique features is their reproductive strategy: the young are born in a r ...

of the family Didelphidae.* It is the only

monotypic In biology, a monotypic taxon is a taxonomic group (taxon) that contains only one immediately subordinate taxon. A monotypic species is one that does not include subspecies or smaller, infraspecific taxa. In the case of genera, the term "unisp ...

species of its

genus Genus (; : genera ) is a taxonomic rank above species and below family (taxonomy), family as used in the biological classification of extant taxon, living and fossil organisms as well as Virus classification#ICTV classification, viruses. In bino ...

, ''Chironectes''. This

semiaquatic In biology, being semi-aquatic refers to various macroorganisms that live regularly in both aquatic and terrestrial environments. When referring to animals, the term describes those that actively spend part of their daily time in water (in ...

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. The term excludes seawater and brackish water, but it does include non-salty mi ...

streams and lakes from

Mexico Mexico, officially the United Mexican States, is a country in North America. It is the northernmost country in Latin America, and borders the United States to the north, and Guatemala and Belize to the southeast; while having maritime boundar ...

through Central and

South America South America is a continent entirely in the Western Hemisphere and mostly in the Southern Hemisphere, with a considerably smaller portion in the Northern Hemisphere. It can also be described as the southern Subregion#Americas, subregion o ...

Argentina Argentina, officially the Argentine Republic, is a country in the southern half of South America. It covers an area of , making it the List of South American countries by area, second-largest country in South America after Brazil, the fourt ...

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 is ...

also has semiaquatic habits). It is also the only extant marsupial species in which both sexes have a pouch. The now extinct

thylacine The thylacine (; binomial name ''Thylacinus cynocephalus''), also commonly known as the Tasmanian tiger or Tasmanian wolf, was a carnivorous marsupial that was native to the Mainland Australia, Australian mainland and the islands of Tasmani ...

, commonly referred to as the Tasmanian tiger, also exhibited this trait. The local name for the water opossum, "yapok", may come from the name of the

Oyapock 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 Guyane in French, is an Overseas departments and regions of France, overseas department and region of France located on the northern coast of South America in the Guianas and the West Indies. Bordered by Suriname to the west ...

Physical appearance

The water opossum is small, measuring long, with a 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 hairless. 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 hind feet 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 A cloaca ( ), : cloacae ( or ), or vent, is the rear orifice that serves as the only opening for the digestive (rectum), reproductive, and urinary tracts (if present) of many vertebrate animals. All amphibians, reptiles, birds, cartilagin ...

.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 hind feet 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 A sex organ, also known as a reproductive organ, is a part of an organism that is involved in sexual reproduction. Sex organs constitute the primary sex characteristics of an organism. Sex organs are responsible for producing and transporting ...

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 (geology), epoch in the geologic time scale that extends from 5.33 to 2.58Holocene The Holocene () is the current geologic time scale, geological epoch, beginning approximately 11,700 years ago. It follows the Last Glacial Period, which concluded with the Holocene glacial retreat. The Holocene and the preceding Pleistocene to ...

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

São Paulo São Paulo (; ; Portuguese for 'Paul the Apostle, Saint Paul') is the capital of the São Paulo (state), state of São Paulo, as well as the List of cities in Brazil by population, most populous city in Brazil, the List of largest cities in the ...

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

Pleistocene The Pleistocene ( ; referred to colloquially as the ''ice age, Ice Age'') is the geological epoch (geology), epoch that lasted from to 11,700 years ago, spanning the Earth's most recent period of repeated glaciations. Before a change was fin ...

–recent cave deposits in

Minas Gerais Minas Gerais () is one of the 27 federative units of Brazil, being the fourth largest state by area and the second largest in number of inhabitants with a population of 20,539,989 according to the 2022 Brazilian census, 2022 census. Located in ...

, Brazil, as well as from the late

Pliocene The Pliocene ( ; also Pleiocene) is the epoch (geology), epoch in the geologic time scale that extends from 5.33 to 2.58Entre Ríos Province Entre Ríos (, "Between Rivers") is a Center Region, Argentina, central provinces of Argentina, province of Argentina, located in the Mesopotamia, Argentina, Mesopotamia region. It borders the provinces of Buenos Aires Province, Buenos Aires (so ...

, Argentina.

Subspecies

*''Chironectes minimus argyrodytes'' Dickey, 1928 - southern

Belize Belize is a country on the north-eastern coast of Central America. It is bordered by Mexico to the north, the Caribbean Sea to the east, and Guatemala to the west and south. It also shares a maritime boundary with Honduras to the southeast. P ...

Guatemala Guatemala, officially the Republic of Guatemala, is a country in Central America. It is bordered to the north and west by Mexico, to the northeast by Belize, to the east by Honduras, and to the southeast by El Salvador. It is hydrologically b ...

El Salvador El Salvador, officially the Republic of El Salvador, is a country in Central America. It is bordered on the northeast by Honduras, on the northwest by Guatemala, and on the south by the Pacific Ocean. El Salvador's capital and largest city is S ...

Honduras Honduras, officially the Republic of Honduras, is a country in Central America. It is bordered to the west by Guatemala, to the southwest by El Salvador, to the southeast by Nicaragua, to the south by the Pacific Ocean at the Gulf of Fonseca, ...

, and northern

Nicaragua Nicaragua, officially the Republic of Nicaragua, is the geographically largest Sovereign state, country in Central America, comprising . With a population of 7,142,529 as of 2024, it is the third-most populous country in Central America aft ...

*''Chironectes minimus paraguensis'' (

Kerr Kerr may refer to: People *Kerr (surname) *Kerr (given name) Places ;United States *Kerr Township, Champaign County, Illinois *Kerr, Montana, A US census-designated place *Kerr, Ohio, an unincorporated community *Kerr County, Texas Kerr Co ...

, 1792) - southeastern

Brazil Brazil, officially the Federative Republic of Brazil, is the largest country in South America. It is the world's List of countries and dependencies by area, fifth-largest country by area and the List of countries and dependencies by population ...

, eastern

Paraguay Paraguay, officially the Republic of Paraguay, is a landlocked country in South America. It is bordered by Argentina to the Argentina–Paraguay border, south and southwest, Brazil to the Brazil–Paraguay border, east and northeast, and Boli ...

, northern

Uruguay Uruguay, officially the Oriental Republic of Uruguay, is a country in South America. It shares borders with Argentina to its west and southwest and Brazil to its north and northeast, while bordering the Río de la Plata to the south and the A ...

, and northeastern

*''Chironectes minimus minimus'' Zimmermann, 1780) - southern

Colombia Colombia, officially the Republic of Colombia, is a country primarily located in South America with Insular region of Colombia, insular regions in North America. The Colombian mainland is bordered by the Caribbean Sea to the north, Venezuel ...

, southern

Venezuela Venezuela, officially the Bolivarian Republic of Venezuela, is a country on the northern coast of South America, consisting of a continental landmass and many Federal Dependencies of Venezuela, islands and islets in the Caribbean Sea. It com ...

Guyana Guyana, officially the Co-operative Republic of Guyana, is a country on the northern coast of South America, part of the historic British West Indies. entry "Guyana" Georgetown, Guyana, Georgetown is the capital of Guyana and is also the co ...

Suriname Suriname, officially the Republic of Suriname, is a country in northern South America, also considered as part of the Caribbean and the West Indies. It is a developing country with a Human Development Index, high level of human development; i ...

, northern and western

, much of

Peru Peru, officially the Republic of Peru, is a country in western South America. It is bordered in the north by Ecuador and Colombia, in the east by Brazil, in the southeast by Bolivia, in the south by Chile, and in the south and west by the Pac ...

, and western

Bolivia Bolivia, officially the Plurinational State of Bolivia, is a landlocked country located in central South America. The country features diverse geography, including vast Amazonian plains, tropical lowlands, mountains, the Gran Chaco Province, w ...

*''Chironectes minimus panamensis'' Goldman, 1914 - southern

Costa Rica Costa Rica, officially the Republic of Costa Rica, is a country in Central America. It borders Nicaragua to the north, the Caribbean Sea to the northeast, Panama to the southeast, and the Pacific Ocean to the southwest, as well as Maritime bo ...

Panama Panama, officially the Republic of Panama, is a country in Latin America at the southern end of Central America, bordering South America. It is bordered by Costa Rica to the west, Colombia to the southeast, the Caribbean Sea to the north, and ...

, northern and western

, northern

, western

Ecuador Ecuador, officially the Republic of Ecuador, is a country in northwestern South America, bordered by Colombia on the north, Peru on the east and south, and the Pacific Ocean on the west. It also includes the Galápagos Province which contain ...

, and northwestern

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 Argentina Marsupials of Bolivia Marsupials of Brazil Marsupials of Colombia Vertebrates of Costa Rica Marsupials of Ecuador Vertebrates of El Salvador Mammals of French Guiana Vertebrates of Guatemala Mammals of Guyana Vertebrates of Honduras Mammals of Mexico Vertebrates of Nicaragua Vertebrates of Panama Mammals of Paraguay Marsupials of Peru Mammals of Suriname Marsupials of Venezuela Mammals of the Caribbean Mammals described in 1780 Extant Pliocene first appearances Taxa named by Eberhard August Wilhelm von Zimmermann