Japanese Spider Crab (Macrocheira kaempferi): The Metazoa Explorer

Japanese Spider Crab (Macrocheira kaempferi)
Photo Credit: Eric Kilby
(CC BY-SA 2.0)

Taxonomic Definition

The Japanese spider crab (Macrocheira kaempferi) is a massive marine benthic decapod recently reclassified into its own distinct monotypic family, Macrocheiridae, diverging from the families Inachidae and Majidae based on larval and genetic analyses. It is endemic to the Pacific Ocean around the coast of Japan, typically inhabiting sandy and rocky substrates at depths ranging from 50 to 500 meters. As the largest living arthropod by leg span, it represents a unique evolutionary trajectory of extreme allometric growth within marine crustaceans.

Hoatzin (Opisthocomus hoazin): The Metazoa Explorer

Hoatzin (Opisthocomus hoazin)
Photo Credit: Charles J. Sharp
(CC BY-SA 4.0)

Taxonomic Definition

Opisthocomus hoazin is the sole extant representative of the family Opisthocomidae and the monotypic order Opisthocomiformes. It is a highly specialized, arboreal folivorous bird endemic to the riparian zones, freshwater swamps, and mangroves of the Amazon and Orinoco river basins in South America.

Vampire Squid (Vampyroteuthis infernalis): The Metazoa Explorer

Vampire Squid (Vampyroteuthis infernalis)
Image Credit: Scientific Frontline / AI generated

Taxonomic Definition

Vampyroteuthis infernalis is a marine cephalopod representing the sole extant member of the order Vampyromorphida and the family Vampyroteuthidae. It is phylogenetically positioned as a sister group to the order Octopoda within the superorder Octopodiformes. The species occupies a circumglobal range, primarily restricted to the meso- and bathypelagic zones of temperate and tropical oceans, specifically within the oxygen minimum zone (OMZ).

Fossa (Cryptoprocta ferox): The Metazoa Explorer

Fossa (Cryptoprocta ferox)
Photo Credit: Ran Kirlian
(CC BY-SA 4.0)

Taxonomic Definition

The fossa (Cryptoprocta ferox) is a carnivorous mammal endemic to Madagascar, classified within the family Eupleridae and the mammalian order Carnivora. It represents the largest extant mammalian apex predator on the island, occupying a diverse range of forested habitats from coastal lowlands to high-altitude mountainous regions.

Bare-hearted Glass Frog (Hyalinobatrachium dianae): The Metazoa Explorer

Bare-hearted Glass Frog (Hyalinobatrachium dianae)adult male.
Image Credit: Brian Kubicki Zootaxa 2015 et al.

Taxonomic Definition

Hyalinobatrachium dianae, formally described in 2015, is a neotropical amphibian classified within the order Anura and the family Centrolenidae. The species is endemic to the Caribbean foothills of Costa Rica, specifically restricted to the premontane wet forests of the Talamanca mountains. Its taxonomic defining feature is a completely transparent ventral parietal peritoneum, which leaves the internal viscera entirely visible from the ventral plane.

Blue Dragon Sea Slug (Glaucus atlanticus): The Metazoa Explorer

Blue Dragon Sea Slug (Glaucus atlanticus)
Photo Credit: Sylke Rohrlach
(CC BY-SA 2.0)

Taxonomic Definition

Glaucus atlanticus is a species of small, pelagic aeolid nudibranch classified within the family Glaucidae and the order Nudibranchia. As an obligate neustonic organism, this species is globally distributed throughout the circumtropical and temperate oceans, primarily occupying the epipelagic zone where it floats inverted at the air-water interface.

Axolotl (Ambystoma mexicanum): The Metazoa Explorer

 Axolotl (Ambystoma mexicanum)
Photo Credit: LoKiLeCh
(CC BY-SA 3.0)

Taxonomic Definition

The axolotl (Ambystoma mexicanum) is a paedomorphic amphibian belonging to the family Ambystomatidae within the order Urodela (Caudata). Historically distributed throughout the high-altitude lakes of the Valley of Mexico, its natural geographic range is currently restricted to the highly modified canal system and wetland remnants of Lake Xochimilco in southern Mexico City.

Tasmanian devil (Sarcophilus harrisii): The Metazoa Explorer

Tasmanian devil (Sarcophilus harrisii)
Photo Credit: JJ Harrison
(CC BY-SA 3.0)

Taxonomic Definition

The Tasmanian devil (Sarcophilus harrisii) is a carnivorous marsupial belonging to the family Dasyuridae within the order Dasyuromorphia. It represents the largest extant carnivorous marsupial globally following the extinction of the thylacine (Thylacinus cynocephalus). Historically distributed across the Australian mainland, its current natural geographic range is strictly endemic to the island state of Tasmania.

American woodcock (Scolopax minor): The Metazoa Explorer

The American woodcock (Scolopax minor)
Photo Credit: Rhododendrites
(CC BY-SA 4.0)

Taxonomic Definition

The American woodcock (Scolopax minor) is a species of wading bird classified within the family Scolopacidae and the order Charadriiformes. Despite its taxonomic placement among shorebirds, it is primarily an upland species endemic to the eastern half of North America. Its geographical range spans from the boreal forests of southern Canada to the Gulf Coast of the United States, predominantly occupying early successional habitats, young forests, and moist woodlands.

Sandhill Cranes (Antigone canadensis)

Sandhill Cranes (Antigone canadensis)
Photo Credit: Frank Schulenburg
(CC BY-SA 4.0)

Taxonomic Definition

Antigone canadensis is a large, terrestrial avian species belonging to the family Gruidae within the order Gruiformes. While historically classified under the genus Grus, comprehensive molecular DNA analyses revealed a distinct evolutionary clade, prompting its reclassification into the genus Antigone alongside species such as the Sarus and White-naped Cranes. The species maintains a vast geographical distribution across North America, with breeding populations extending into northeastern Siberia and isolated, non-migratory populations situated in the southeastern United States and Cuba.

Wild red-tailed bumblebees (Bombus lapidarius): The Metazoa Explorer

Wild red-tailed bumblebees (Bombus lapidarius)
Left queen | Right drone
Photo Credit: Ivar Leidus
Changes made: Combined images
(CC BY-SA 4.0)

Taxonomic Definition

Bombus lapidarius is a species of eusocial bumblebee classified within the order Hymenoptera, the family Apidae, and the subgenus Melanobombus. Its primary geographical range encompasses the Palearctic realm, widely distributed across temperate regions of Europe and extending into Western Asia and parts of Northern Africa.

Mediterranean monk seal (Monachus monachus): The Metazoa Explorer

Mediterranean monk seal (Monachus monachus)
Photo Credit: Marinko Babić
(CC BY-SA 4.0)
Changes made: Enhanced color and sharpness

Taxonomic Definition

The Mediterranean monk seal (Monachus monachus) is a marine mammal belonging to the family Phocidae (earless seals) within the order Carnivora. Once distributed widely throughout the Mediterranean Sea, the Black Sea, and the North Atlantic coast of Africa, its extant geographical range is now severely restricted and fragmented. Current demographics are largely confined to isolated populations in the eastern Mediterranean basin, the Cabo Blanco peninsula on the Atlantic coast of Africa, and the Madeira archipelago.

Muskrat (Ondatra zibethicus): The Metazoa Explorer

Muskrat (Ondatra zibethicus)
Photo Credit: D. Gordon E. Robertson
(CC BY-SA 3.0)

Taxonomic Definition

The muskrat (Ondatra zibethicus) is a medium-sized, semiaquatic rodent classified within the order Rodentia and the family Cricetidae, belonging specifically to the subfamily Arvicolinae alongside voles and lemmings. It is the sole extant member of the genus Ondatra and is endemic to a vast geographical range across North America, spanning from the Canadian treeline to the northern border of Mexico. Due to historical fur-trade introductions, it has also established extensive, often invasive, populations throughout the riparian and wetland ecosystems of Europe, Asia, and South America.

Bilby (Macrotis): The Metazoa Explorer

Taxonomic Definition

The genus Macrotis, commonly known as bilbies, represents a distinct lineage of desert-dwelling marsupial omnivores classified within the family Thylacomyidae and the order Peramelemorphia. Historically distributed across roughly 70% of the Australian landmass, their primary geographical range is now severely restricted to isolated, arid and semi-arid patches in the Northern Territory, Western Australia, and southwestern Queensland.

Wolverine (Gulo gulo): The Metazoa Explorer

Wolverine (Gulo gulo)
Photo Credit: Spencer Wright
(CC BY 2.0)

Taxonomic Definition

Gulo gulo is a terrestrial carnivorous mammal belonging to the family Mustelidae within the order Carnivora, representing the largest land-dwelling species of its family. Its geographic distribution encompasses the boreal forests, taiga, and alpine tundra regions of the Northern Hemisphere, spanning North America, Europe, and Asia.

Arabian fat-tailed scorpion (Androctonus crassicauda): The Metazoa Explorer

Arabian fat-tailed scorpion (Androctonus crassicauda)
Photo Credit: Per-Anders Olsson
(CC BY-SA 4.0)
Changes made: Enhanced and enlarged by Scientific Frontline

Taxonomic Definition

The Arabian fat-tailed scorpion (Androctonus crassicauda) is a highly venomous arachnid classified within the family Buthidae and the order Scorpiones. As a generalist desert species, its primary geographical range encompasses the Palearctic region, spanning across the Middle East—including Saudi Arabia, Iran, Iraq, Israel, Syria, Jordan, and Turkey—as well as the Sinai Peninsula in North Africa.

Siberian crane (Leucogeranus leucogeranus): The Metazoa Explorer

Siberian crane (Leucogeranus leucogeranus)

Taxonomic Definition

The Siberian crane (Leucogeranus leucogeranus) is a large, critically endangered avian species belonging to the family Gruidae within the order Gruiformes. It represents a monotypic lineage, functioning as the sole extant member of the genus Leucogeranus. Its primary geographical range spans vast migratory corridors across Eurasia, with breeding grounds restricted to the Arctic tundra of Russia and principal wintering grounds localized in the middle and lower Yangtze River Basin in China, alongside a relic wintering site in Iran.

Blue-sided leaf frog (Agalychnis annae): The Metazoa Explorer

Blue-sided leaf frog (Agalychnis annae)
Photo Credit: Charles J. Sharp
(CC BY-SA 4.0)

Taxonomic Definition

Agalychnis annae is a nocturnal arboreal anuran belonging to the family Phyllomedusidae and the order Anura. Endemic to Costa Rica, its primary distribution is restricted to the Central Valley and the adjacent slopes of the Cordillera de Talamanca and Cordillera Central, where it inhabits premontane moist forests and, increasingly, anthropogenic environments.

Eastern Hercules beetle (Dynastes tityus): The Metazoa Explorer

Eastern Hercules beetle (Dynastes tityus) Male
Photo Credit: David Hill
(CC BY 4.0)

Female
Photo Credit: Fredlyfish4
(CC BY 4.0)

Taxonomic Definition

Dynastes tityus is a coleopteran arthropod belonging to the family Scarabaeidae and the subfamily Dynastinae (rhinoceros beetles). It is the heaviest and one of the largest beetles native to the United States, with a distribution primarily confined to the deciduous forests of the eastern and southeastern United States, ranging from New York to Florida and west to Texas.

Shoebill Stork (Balaeniceps rex): The Metazoa Explorer

Shoebill Stork (Balaeniceps rex)
Photo Credit: Hans Hillewaert
(CC BY-SA 3.0)

Taxonomic Definition

Balaeniceps rex is a large, monotypic avian species comprising the sole extant member of the family Balaenicipitidae. Historically classified within Ciconiiformes (storks), modern molecular phylogenetics places it within the order Pelecaniformes, closely allied with pelicans and hamerkops. Its range is strictly limited to the freshwater swamps and extensive papyrus wetlands of East-Central Africa, primarily in South Sudan, Uganda, western Tanzania, and northern Zambia.