Identification Photos: Sand Swim Crab, Arenaeus mexicanus: The Sand Swim Crab is characterized by having nine tooth-like extensions, or spikes, along the side of its shell that commence at the eyes and run about halfway back on the shell or carapace. The last of these “teeth” is very long with some curvature.

The Sand Swim Crab has a unique claw shape with a characteristic and identifying spike present just behind the base. Its reaches a maximum size of 3 inches and is normally found up to 200 feet deep in the water column.

In Mexico, the Sand Swim Crab is found in the lower two-thirds of the Sea of Cortez, from Magdalena Bay south along the Pacific side of the Baja California peninsula, along the coast of the mainland south to Guatemala and around the oceanic islands. The Sand Swim Crab can be easily confused with the Giant Swim Crab, Callinectes toxotes (unique “tooth” pattern between the eyes), and the Rough Swim Crab, Portunus asper (straight ninth “tooth”).

The Sand Swim Crab is a member of the Portunidae Family of Swimming Crabs, known in Mexico as Jaibas. They have been classified into 13 Genuses of which five with 16 individual species are found in Mexican waters. They consume clams, fish, snails, worms and other crustaceans.

The commercially important Blue Crab, Callinectes sapidus, is a member of this family. They are decapods with ten limbs.

Swim Crabs are colorful and active crabs that are among the few crabs that are swift and agile swimmers. They swim sideways utilizing their paddle-like fifth pair of (dactyl) legs that rotate like propeller blades when they swim. However, they are essentially bottom dwellers. They have a streamlined profile that allows for rapid swimming and long pincers armed with sharp spines to snag food.

Sand Swim Crab, Arenaeus mexicanus: Male (upper two photos) and female (lower two photos). Shows up when one purchases a “scoop of bait.” Caught in the surf zone, La Playita, San Jose del Cabo, Baja California Sur, Mexico, during the month of July with water temperatures around 83 degrees, early morning in 5 to 10 foot deep water utilizing a cast net by panguero bait salesmen. Size approximately 3 inches and they “bite like hell!” Not viewed by locals to be of great value. Does survive a panga “bait tank” at a high level. Worth sending “down deep” to see what materializes. Description and photos courtesy John Snow.