Crab
Guides
Armases
square-back American marsh crabs
Armases is a genus of sesarmid crabs comprising approximately 13 described species distributed across tropical and subtropical coastal regions of the Americas. These semi-terrestrial crabs inhabit salt marshes, mangroves, and estuarine environments, with some species exhibiting notable movement between marine and terrestrial habitats. Several species have been extensively studied for their larval development, metabolic ecology, and role in ecosystem energy transfer. The genus includes both species with larval export strategies to continental shelves and those breeding in supratidal rock pools.
Armases cinereum
squareback marsh crab, wharf crab
Armases cinereum is a small, dark brown crab native to Atlantic and Gulf coasts of North America. It inhabits intertidal zones from salt marshes to mangrove swamps, often found under rocks and debris. The species is highly omnivorous, consuming detritus, plant material, and small invertebrates. It is notable for extensive mobility between marsh and upland habitats, with females exhibiting wider ranging movements that may transport energy between ecosystems.
Calappidae
Box Crabs
Calappidae is a family of marine crabs commonly known as box crabs, comprising approximately 16 genera including both extant and fossil taxa. Seven genera are known only from the fossil record, with calappid fossils documented from the Cretaceous to Recent (66.043 Ma to present) across Europe, the United States, Mexico, Central America, Australia, and Japan. The family is characterized by a distinctive box-like carapace morphology and is distributed in tropical and temperate marine waters worldwide.
Cancer
Edible Crabs
Cancer is a genus of marine crabs in the family Cancridae, comprising eight extant species and three extinct species. The genus includes economically and ecologically important species such as the European edible crab (Cancer pagurus), Jonah crab (Cancer borealis), and red rock crab (Cancer productus). These crabs inhabit littoral and sublittoral zones of temperate and cold-temperate seas, primarily in the Atlantic and Pacific Oceans. The genus is thought to have evolved from related Pacific Ocean genera during the Miocene epoch.
Cancer gracilis
Cancer gracilis is a species of true crab in the family Cancridae, originally described by Dana in 1852. It is currently recognized as a synonym of Metacarcinus gracilis. The species belongs to the diverse group of decapod crustaceans characterized by a hard carapace and ten walking legs. Like other members of the genus, it is a marine crab found in coastal waters.
Carcinus
Green crabs
Carcinus is a genus of crabs in the family Carcinidae, comprising two recognized species: C. maenas (the European green crab or shore crab) and C. aestuarii (the Mediterranean shore crab). The genus is notable for containing one of the world's most successful marine invasive species, C. maenas, which has established populations across temperate coastlines on multiple continents. Both species share similar ecological roles as opportunistic predators in coastal marine systems. C. aestuarii is endemic to the Mediterranean Sea and has been implicated in at least one invasion event in Japan.
Dyspanopeus sayi
Say's mud crab, small mud crab
Dyspanopeus sayi is a small mud crab native to the western Atlantic coast of North America, ranging from eastern Canada to Florida. It has become a successful invasive species in European waters, first detected in Wales in 1960 and subsequently spreading to the Mediterranean Sea, North Sea, Black Sea, and most recently the Sea of Azov. The species inhabits muddy bottoms from the intertidal zone to depths of 46 meters and is an active predator of bivalve molluscs and barnacles. It reaches sexual maturity within one year and has a maximum lifespan of approximately two years.
Grapsus grapsus
Sally Lightfoot Crab, Red Rock Crab, Abuete Negro
Grapsus grapsus is a common intertidal crab native to the Pacific and Atlantic coasts of the Americas. Adults display highly variable coloration ranging from brownish-red to mottled yellow and pink, while juveniles are darkly colored for camouflage on volcanic substrates. The species is renowned for its agility and rapid escape response, making it difficult to capture. It occupies rocky shorelines just above the spray zone and has been documented engaging in cleaning symbiosis with marine iguanas in the Galápagos.
Hemigrapsus
Hemigrapsus is a genus of varunid crabs containing fifteen recognized species. The genus is naturally distributed almost exclusively in the Pacific Ocean, with one species endemic to the Atlantic coast of South America. Two species—H. sanguineus and H. takanoi—have been introduced from East Asia to the North Atlantic region, where they have established invasive populations along European coasts and the eastern United States. One species, H. estellinensis, is considered extinct; it was endemic to a hypersaline spring in the Texas Panhandle.
Hemigrapsus nudus
Purple Shore Crab
The purple shore crab (Hemigrapsus nudus) is a small intertidal crab native to the Pacific coast of North America. It shelters under rocks in the mid to high intertidal zone and feeds primarily on green algae, particularly sea lettuce. The species is distinguished from similar shore crabs by its purple coloration and smooth carapace lacking prominent teeth or spines between the eyes.
Leucosiidae
Purse Crabs
Leucosiidae is a family of marine crabs commonly known as purse crabs. The family contains three subfamilies and several genera of uncertain placement. Members are characterized by their rounded, often smooth carapaces that resemble small purses or pebbles. The family was established by George Samouelle in 1819.
Ocypode
Ghost Crabs
Ocypode is a genus of ghost crabs comprising 21 species distributed across tropical and subtropical sandy shores worldwide. Members are characterized by deep box-like bodies, elongated eyestalks often tipped with horn-like projections in several species, and pronounced claw asymmetry with one cheliped substantially larger than the other. They construct deep burrows in intertidal sandy or muddy substrates and exhibit primarily nocturnal activity patterns. The genus was established in 1795 and remained the sole genus in subfamily Ocypodinae until 2013, when Hoplocypode was segregated based on gonopod morphology.
Ovalipes ocellatus
Lady Crab, Ocellated Crab, Calico Crab, Leopard Crab, Atlantic Leopard Crab
Ovalipes ocellatus, commonly known as the Lady Crab, is a medium-sized crab species native to the western Atlantic coast of North America. The species is distinguished by its yellow-grey to light purplish carapace adorned with distinctive leopard-like clusters of purple spots, which provide limited iridescence for signaling. It is primarily nocturnal and often buries itself in sandy substrates. The species has been described as notably aggressive toward humans, with documented instances of pinching waders.
Persephona
mottled purse crab (for P. mediterranea)
Persephona is a genus of true crabs in the family Leucosiidae, established by Leach in 1817. The genus contains approximately five described species, including the mottled purse crab (P. mediterranea). These crabs belong to the purse crab family, characterized by their rounded, often box-like carapaces. Species in this genus are found in marine environments, with records from the Atlantic and Mediterranean regions.