Aratus pisonii (Milne-Edwards, 1837) - mangrove tree crab in Florida, USA (January 2016).

The crustaceans are a large group of arthropods that inhabit marine, marginal marine, freshwater, and terrestrial habitats. The crustaceans include crabs, lobsters, shrimp, crayfish, barnacles, ostracods, and other organisms. The oldest fossil crustaceans are in the Cambrian. The group experienced a significant radiation in the oceans during the Mesozoic Marine Revolution.

The mangrove tree crab shown above occupies mangrove swamp environments. It usually lives among red mangroves - Rhizophora mangle (en.wikipedia.org/wiki/Rhizophora_mangle). At low tide, the crabs are near or on the ground. During high tide, they ascend tree trunks, often to relatively high levels. Mangrove tree crabs are omnivorous - they are principally herbivores, feeding on mangrove foliage, but are also detritovores, scavengers, and predators on small invertebrates and some protists.

Classification: Animalia, Arthropoda, Crustacea, Malacostraca, Decapoda, Brachyura, Sesarmidae

Locality: tree along boardwalk to Mangrove Overlook, Ding Darling National Wildlife Refuge, Sanibel Island, southwestern Florida, USA

More info. at: en.wikipedia.org/wiki/Crustacean and