AnimaliaHighest rank in taxonomy. Groups all life into domains: Animalia, Plantae, Fungi, etc.IUCN LCInternational Union for Conservation of Nature — the world authority on species extinction risk, using standardized criteria. — Least Concern — widespread and abundant; not at immediate risk of extinction.In ProgressCurrent stage of this record in the editorial review workflow. Recent Sighting
Chironectes minimus
Water Opossum / Yapok
(Zimmermann, 1780)
Detailed Texts Multi-lang
The water opossum (Chironectes minimus) is the only truly semi-aquatic marsupial on the planet. It is a medium-sized animal with dense, short, and water-repellent fur, adorned with a striking marbled pattern of light gray and dark black stripes. It possesses exceptional aquatic adaptations: its hind feet are broad and fully webbed (interdigital membrane) like a duck's, while its front feet lack webbing but have long, agile fingers to feel for and catch prey underwater. Its tail is long, thick, furry at the base and bare for the rest, used as a rudder when swimming. It is an elusive and fascinating animal representing a marvel of convergent evolution with otters.
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Julia Trouin
TaxonomyBiological classification ranks placing this species within the tree of life, from Kingdom down to Genus.
PhylumRank below Kingdom. Groups organisms sharing a fundamental body plan (e.g., Chordata = vertebrates and some invertebrates).Chordata
ClassRank below Phylum. Subdivides by structural traits (e.g., Mammalia, Aves, Reptilia, Insecta).Mammalia
OrderRank below Class. Groups related families sharing common ancestry (e.g., Carnivora, Primates).Didelphimorphia
FamilyRank below Order. Groups closely related genera (e.g., Felidae = cats, Canidae = dogs).Didelphidae
GenusRank just above Species. The first word in the two-part binomial scientific name.Chironectes
Taxonomic AuthorityThe scientist who first formally described and published this species, followed by the year of publication.(Zimmermann, 1780)
Record Completeness
85%Coming soon
Ecology & StatusHow this species lives: habitat preferences, diet, behavior, population status, and role in its ecosystem.
OriginWhether the species is native (evolved here), endemic (found only here), or introduced by human activity.
Native
Population TrendDirection of change in population size over time: increasing, stable, decreasing, or unknown.
Decreasing
Breeding SeasonTime of year when this species typically reproduces or flowers.
Year Round
Trophic RolePosition in the food chain: producer, herbivore, carnivore, omnivore, decomposer, or parasite.
Carnivore
Recent SightingsWhether this species has been observed in the wild in Costa Rica within recent years.
Yes
Habitat SummaryOverview of the specific ecosystems and environments where this species is found in Costa Rica. Multi-lang
It is a strict specialist of freshwater habitats. It resides in rivers, clear fast-flowing streams, lakes, and wetlands of tropical and subtropical forests (both primary and mature secondary). It relies on stable, forested riverbanks where it can dig its burrows just above the water level. In Costa Rica, it is found in lowland and mid-elevation zones on both slopes, though sightings are rare due to its nocturnal habits and elusive nature.BehaviourDaily activity patterns, movement, territory use, foraging style, and seasonal behavioral changes. Multi-lang
It is a strictly nocturnal and solitary hunter. At nightfall, it emerges from its burrow to hunt in rivers and streams. It is an extraordinary and agile diver, swimming with alternating strokes of its hind legs. Its hunting method consists of swimming along the bottom, feeling stones and crevices with its agile front feet extended forward to catch crustaceans, aquatic insects, frogs, and small fish. Its fur retains air, keeping its skin dry and warm under cold water.Social ActivitySocial structure: whether the species is solitary, paired, or colonial; hierarchy and communication. Multi-lang
Strictly solitary. Sexes only meet briefly for copulation.Feeding GuildWhat the species eats, how it forages or hunts, and its role as a consumer in the food web. Multi-lang
Carnivore / Piscivore / Insectivore.Trophic Chain DetailsSpecific interactions in local food webs: prey species, predators, competitors, and scavengers. Multi-lang
Carnivore (Aquatic specialist). Apex predator of small riparian micro-ecosystems. Occasionally hunted by jaguars, ocelots, caimans, large water snakes (like anacondas or large boas), and nocturnal raptors.Reproductive BehaviourMating strategies, courtship displays, nesting or spawning behavior, and parental care. Multi-lang
Breeds year-round in tropical zones, but with a peak during the dry season. Gestation is about 12 to 14 days. The young (usually 1 to 5) are born tiny and migrate to the mother's watertight marsupium. Incredibly, they can survive without breathing for several minutes inside the closed pouch while the mother dives, thanks to their low metabolic rate and hypoxia tolerance. After 20 days they grow fur, and weeks later they open their eyes, at which point they no longer fit in the pouch and wait in the burrow while the mother hunts.Physical Measures
Length (cm)
27.0 - 32.0 cm
Weight (Grams)
600 g - 800 g
Offspring per cycleTypical number of young (live births, eggs, or seeds) produced by one adult in a single reproductive event or breeding season.1 - 5
Sexual DimorphismObservable physical differences between males and females of the same species (e.g., size, coloration, features).Yes
Lifespan
Sexual MaturityAge at which the individual becomes capable of reproducing for the first time.
10 - 12 Months
Gestation / IncubationDuration from fertilization to birth (mammals) or to hatching (egg-laying species).
12 - 14
Lifespan EstimatedExpected duration of life from birth to natural death under wild conditions.
Males2 - 3 Years
Females2 - 3 Years
Sexual DimorphismPhysical differences in size, coloration, or morphology between males and females of this species.
Males Multi-lang
Possess a non-reproductive marsupium to protect their scrotum from mechanical damage and drag while swimming.
Females Multi-lang
Possess a reproductive marsupium with strong sphincter muscles to seal it underwater.
Evolutionary AdaptationsInherited traits and behaviors that improve the species' survival and reproduction in its specific environment. Multi-lang
Watertight Marsupium (Both Sexes): Both females and males possess a marsupium. In females, a ring of strong sphincter muscles seals the pouch hermetically, creating a watertight compartment that allows the young to survive dry and oxygenated while the mother dives. In males, the pouch protects the genitals from submerged branches and rocks and reduces hydrodynamic drag when swimming.
Webbed Hind Feet and Sensory Hands: Its hind feet act as powerful paddles thanks to extensive interdigital webbing. Its front feet lack webbing, but its fingers are extremely sensitive and used to feel the bottom of muddy streams in the dark, catching crustaceans without needing to see them.
Main ThreatsDocumented pressures reducing the population: habitat loss, hunting, disease, climate change, and invasive species. Multi-lang
Water Pollution and Aquatic Alteration: They are extremely sensitive to water pollution from agrochemicals and sedimentation, which destroys their food sources (crustaceans and fish).
Riparian Deforestation: The logging of gallery forests removes the roots and logs where they build their underground burrows, leaving them without shelter.
Interesting FactsSurprising or notable facts that highlight what makes this species unique or ecologically important. Multi-lang
Unique Marsupial in the World: It is the only living marsupial where both sexes have a functional marsupium (though for different purposes).
Underground Construction: They build complex tunnels in riverbanks, where the entrance tunnel is hidden just at water level but slants upward to a dry leaf-lined chamber where they rest during the day.