Loxorhynchus grandis

Distinguished from other eastern Pacific spider crabs by the combination of large size, tear-shaped tuberculate carapace, and the distinctive down-curved, notched preorbital spine. Juveniles under 8 cm can be identified by their active decoration behavior—attaching algae, bryozoans, hydroids, and sponges to the exoskeleton—which adults do not exhibit. The extremely long second walking legs are diagnostic among regional majoid crabs.

Large crab with tear-shaped carapace covered in short spines (tubercles). Carapace tapers to a pointed rostrum with a sharply down-curved, deeply notched preorbital spine at the tip. Second pair of walking legs longest, exceeding carapace width and allowing overall span up to 57 cm. Exoskeleton typically reddish, brown, or blue-green in color; adults often appear green due to algal growth on the long-lived shell.

Marine coastal waters on soft and rocky bottoms, as well as artificial structures such as pilings. Depth range 6–152 meters. Seasonally migratory: occupies shallow waters during warm months and moves to deeper waters during cooler months.

Eastern Pacific Ocean from Cordell Bank, California (USA) south to Punta San Bartolome, Baja California (Mexico).

Adults migrate seasonally: shallow waters (warmer months), deeper waters 6–152 m (cooler months). Brooding females observed year-round, indicating no strong seasonal peak in reproduction.

Scavenger-generalist: consumes algae, mussels, sea stars, small crabs (including juveniles of conspecifics and northern kelp crabs Pugettia producta), and dead fish.

Gonochoric (separate sexes). Internal fertilization; females store sperm and brood 125,000–500,000 eggs glued to abdomen. Egg development indicated by color change: orange (fresh), red (intermediate), brown (eyed, ready to hatch). Larvae are planktonic; settle at approximately 1 cm carapace width. Growth via periodic molting until terminal molt at sexual maturity, after which growth and limb regeneration cease. Minimum lifespan at least 3 years; maximum unknown.

Forms aggregations of dozens to hundreds of adults, hypothesized to function in mate-finding through pheromone concentration. Typically solitary outside aggregations. Mobile forager achieving speeds up to 0.4 km/h. Juveniles actively decorate exoskeleton with organisms for camouflage; adults cease decoration above 8 cm size. Adults may develop algal coating on exoskeleton due to long inter-molt period.

Predator and scavenger on benthic communities; prey item for diverse marine predators including sea otters, cabezon, California sheephead, octopus, sharks, bat rays, California sea lions, and larger conspecifics. Juvenile decoration behavior may facilitate transport of sessile organisms.

Subject to commercial fishery in California since late 1970s, with markets for male claws and whole crabs. Landings peaked in 1988 (96,000 lb claws, 108,000 lb whole crabs). Fishery declined significantly after 1990 California ballot initiative banned gill nets and trammel nets. 2018 landings: 503 lb claws, 74,863 lb whole crabs. Taken as bycatch (1.29%) in California spiny lobster fishery.

• Pugettia producta (Northern Kelp Crab)Overlapping range and habitat; distinguished by smaller maximum size, different carapace shape, and absence of the notched preorbital spine characteristic of L. grandis. Preyed upon by adult sheep crabs.

• BugGuide
• Wikipedia
• GBIF taxonomy match
• iNaturalist taxon
• NCBI Taxonomy
• Catalogue of Life
• Guest Blog Post: Researchers split the birdcatcher trees (genus Pisonia) into three | Blog
• Bug Eric: Wasp Wednesday: Western Cicada Killer
• Nomenclatural changes in Phymatodes | Beetles In The Bush