Portunidae
Guides
Achelous
Achelous is a genus of swimming crabs in the family Portunidae, established by De Haan in 1833. These marine brachyuran crabs are characterized by their flattened, streamlined bodies and modified fifth pereiopods adapted for swimming. The genus includes commercially significant species such as A. spinimanus, a fishery resource in southeastern Brazil, and A. hastatus, distributed across the Atlantic-Mediterranean region. Species within this genus exhibit habitat preferences related to sediment type and depth, with some showing age and sexual segregation patterns typical of portunid crabs.
Achelous spinimanus
Blotched Swimming Crab
Achelous spinimanus is a swimming crab native to the Western Atlantic, ranging from the USA to Brazil. It inhabits coastal marine environments from shallow waters to 90 m depth, with distinct depth preferences between life stages: juveniles occur at 5–35 m while adults are most abundant at 25 m and range to 40 m. The species exhibits continuous year-round reproduction with ovigerous females present in all seasons, and shows seasonal migration patterns in response to water temperature and salinity changes. It is an emerging fishery resource in Brazil, where it has become a target species following declines in more traditional catches.
Portunus sayi
Sargassum Swimming Crab
Portunus sayi is a pelagic swimming crab endemic to floating Sargassum seaweed mats in the western Atlantic Ocean and Caribbean Sea. It exhibits specialized adaptations for swimming, including paddle-shaped fourth legs that enable rapid sideways movement. The species relies on chemical, visual, and tactile cues to locate and select host Sargassum patches, demonstrating strong host fidelity. Recent records from the Amazon continental shelf represent the northernmost observation in Brazilian waters, expanding its known range.