American Pebble Crab, Daira americana

American Pebble Crab, Daira americana. Underwater photographs taken in Zihuatanejo Bay, Guerrero, January 2022. Photographs and identifications courtesy of Ron Woheau, Zihuatanejo, Guerrero. Identification courtesy of Daniel Eisenhauer.

General information: The American Pebble Crab, Daira americana (Stimpson, 1860), is a member of the Dairidae Family of Brachyuran Crabs, and are known in Mexico as Cangrejo Piedra Americano and Cangrejo Yeti Oriental. There are three Genera in the Dairidae Family and fourteen species in the Daira Genus. They are highly territorial animals, defending their space by attacking or waving their claws.

Identification: The American Pebble Crab has an oval profile and has a tan shell or carapace with dark brown round lumps with purple tinges around the eyes and mouth.  The carapace has a granulated texture setae between the dense tubercles with smaller lumps on the anterior margin Their claws are large and highly tuberculate with a unique bumpy structure and a medium brown. The carapace are 2.5 cm (1.0 inch) in width and 1.7 cm (0.7 inches) in depth. The American Pebble Crab can be easily confused with the Lumpy Claw Crab, Eriphia squamata (very tuberculae claws with fewer lumps on the carapace with eriphiid sharp anterolateral teeth).

Habitat and Range: The American Pebble Crab are dominant animals found in abundance in rocky and coral intertidal (between the high and low tide) regions. They shelter during daylight hours among coral rubble, under rock, and within reef crevices where surge and wave action are moderate. The American Pebble Crab is found in all Mexican waters of the Pacific Ocean.

Diet: The American Pebble Crab are nocturnal predator’s being omnivorous reef scavengers and grazers, feeding on algae, small invertebrates, and organic detritus that they scrap from hard surfaces.

Conservation Status: The American Pebble Crab has not been formally evaluated from a conservation status. However, they are common and of limited interest to most and should be considered to be of Least Concern. Caution: The American Pebble Crab is reported to be toxic to humans.