Cardisoma

Distinguished from the related genus Discoplax (which formerly contained three species now separated from Cardisoma) by morphological and genetic characteristics. The moderate claw asymmetry separates Cardisoma from Uca, which shows extreme enlargement of one claw in males. The combination of large body size, semi-terrestrial burrowing habit, and coastal distribution distinguishes it from strictly aquatic crab genera. Juvenile coloration is distinctive but not diagnostic without geographic and habitat context.

Large-bodied crabs with a broad, domed carapace. Juveniles exhibit vivid coloration: purple-blue carapace with orange-red legs. Color intensity diminishes with age; adult coloration becomes duller, with females typically less vivid than males. One claw is markedly enlarged relative to the other, though the asymmetry is less pronounced than in fiddler crabs (genus Uca). Sexual dimorphism in size and color saturation has been documented.

Warm coastal regions with access to groundwater. Natural habitats include mangrove forests with soft, clayey substrates, hydroperiods, humid soils, and shade from mangrove species (Rhizophora mangle, Laguncularia racemosa, Avicennia germinans). Also occupies transformed environments such as pastures, provided burrows can reach the water table. Burrows are typically constructed 300 m to 5 km inland from the sea. Soil hardness negatively affects population density.

Tropical and subtropical coastal regions: southern Florida through the Caribbean to Brazil, including Caribbean islands; West Africa. In Mexico, occurs along Caribbean and Gulf of Mexico coasts (documented from 18.14°–23.78°N; 94.14°–97.90°W).

Adults active during September and October in sampled Gulf of Mexico populations. Year-round activity likely in tropical portions of range, with seasonal breeding migrations to marine habitats.

Omnivorous, with plant material as primary food source.

Semi-terrestrial adults inhabit burrows inland from the sea. Females undertake periodic migrations to marine waters to spawn. Larval stages are strictly marine and pelagic, developing in coastal waters. Early developmental stages are marine; juveniles transition to terrestrial burrow habitats.

Constructs and maintains burrows in both natural and disturbed habitats, requiring connection to groundwater for survival. Females exhibit periodic seaward migration for spawning. Burrow temperature at deepest accessible point has been recorded as a microhabitat variable.

Subject to commercial exploitation; threatened by harvesting pressure in parts of range. Juveniles collected for pet trade due to attractive coloration. Occupies both natural and anthropogenically modified landscapes, indicating some resilience to habitat transformation provided water table access is maintained.

• DiscoplaxThree species formerly classified in Cardisoma are now placed in Discoplax based on morphological and genetic revision.
• Uca (fiddler crabs)Both exhibit claw asymmetry, but Uca shows extreme enlargement of one claw (especially males) and occupies intertidal mudflat habitats rather than inland burrow systems.

• BugGuide
• Wikipedia
• GBIF taxonomy match
• iNaturalist taxon
• NCBI Taxonomy
• Catalogue of Life
• Variation in the Adult Sex Ratio and Morphological Traits of Cardisoma guanhumi (Latreille, 1828) in Contrasting Habitats in the Southwest of the Gulf of Mexico.