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 a po ...
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 extant taxon, living and fossil organisms as well as Virus classification#ICTV classification, viruses. In the hierarchy of biological classification, genus com ...
, ''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
Semiaquatic animals include:
* Verte ...
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 include ...
streams and lakes from Mexico through Central and South America to Argentina and is the most
aquatic living marsupial (the
lutrine opossum 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 Tasman ...
, 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, craniate, gill-bearing animals that lack limbs with digits. Included in this definition are the living hagfish, lampreys, and cartilaginous and bony fish as well as various extinct related groups. Approximately 95% of li ...
,
crustacean
Crustaceans (Crustacea, ) form a large, diverse arthropod taxon which includes such animals as decapods, seed shrimp, branchiopods, fish lice, krill, remipedes, isopods, barnacles, copepods, amphipods and mantis shrimp. The crustacean group ...
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 France, French Overseas departments of France, overseas department of French Guiana and the Brazilian States of Brazil, state of Amapá. ...
in
French Guiana
French Guiana ( or ; french: link=no, Guyane ; gcr, label=French Guianese Creole, Lagwiyann ) is an overseas departments and regions of France, overseas department/region and single territorial collectivity of France on the northern Atlantic ...
.
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, a ...
.
[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.
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 2.58[Holocene
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 togethe ...](_blank)
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 GaWC a ...
, 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 (literally ...
, 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 2.58[Entre 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 ( ...](_blank)
, 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