Pacific Arrow Crab, Stenorhynchus debilis

Pacific Arrow Crab, Stenorhynchus debilus.  Collected from a tidal pool at Km 17, El Tule, Baja California Sur, February 2007. Size: 1.0 cm (0.4 inches) x 2.0 cm (0.8 inches).

Pacific Arrow Crab, Stenorhynchus debilus.  Regurgitated by a 30 cm Goldspotted Sand Bass caught in coastal waters off Loreto, Baja California Sur, August 2024. Wing Span: 20 cm (7.9 inches).

Pacific Arrow Crab, Stenorhynchus debilus. Underwater photograph taken in Zihuatanejo Bay, Guerrero, March 2018. Photograph courtesy of Ron Woheau, Zihuatanejo.

Pacific Arrow Crab, Stenorhynchus debilus. Underwater photographs taken in Zihuatanejo Bay, Guerrero, December 2019 and March 2022. Photographs courtesy of Maude Jette, Dive Zihuatanejo, www.Divezihuatanejo.com.

General information: The Pacific Arrow Crab, Stenorhynchus debilus, is common decapod (with ten legs) that is found in most tropical waters and is a member of the Inachidae Family of Arrow Crabs. They are known in Mexico as congrejo flecha.

Identification: The Pacific Arrow Crab is characterized by triangular carapace (shell) and very long spider-like arms and legs with the rostrum as long or longer than the carapace lined with short defensive spikes. The rostrum and carapace resemble a large teardrop.  The shells reach a maximum of 2.5 cm (1.0 inch) in length and they can reach a full 10 cm (3.9 inches) across when the legs are extended. They can be found with a pink to reddish brown carapace but have been known to sport a bright green both with bright yellow/gold steaks. the fingers of the chelae are reddish as well.

Habitat and Range: The Pacific Arrow Crabs are found in rocky, intertidal (between the high and low tide) regions in and near reef crevices, but are often found in deeper waters up to 60 m (200 feet) by scuba or trawling. They are found in all Mexican waters of the Pacific including throughout the Sea of Cortez and south to Chile and the Galapagos islands; during years with El Niño’s they can be found in the coastal waters of southern California.

Diet: The Pacific Arrow Crab is an nocturnal omnivore they preys predominately on algae and small gastropods (mostly snails).

Conservation Status: The Pacific Arrow Crab has not been formally evaluated from a conservation status.  However, they are common, small in stature and of limited interest to most and should be considered to be of Least Concern.

Synonyms:  Leptopodia debilis and Leptopodia sagittaria