Why the Majoidea superfamily includes the world's largest and most peculiar crab species

Nature · Published 3 October 2026 Swipe more like this →

In short: The Majoidea superfamily, encompassing both spider and decorator crabs, represents a diverse group of crustaceans found across global oceans. From the massive Japanese spider crab dwelling on the Pacific floor to the social, clambering crabs of Tasmania, these arthropods exhibit fascinating behaviors and physical adaptations that define their unique evolutionary lineage.

The Majoidea superfamily is a complex taxonomic group that has undergone significant classification revisions over time. While early studies, such as those by De Grave and colleagues, initially organized these crabs into six distinct families, modern understanding has evolved. Recent taxonomic shifts include the elevation of the subfamilies Epialtinae and Mithracinae to full family status, while the group Hymenosomatidae was relocated to its own separate superfamily, refining our grasp of their biological relationships.

Among the most notable members of this group is the Japanese spider crab, Macrocheira kaempferi. Recognized as the largest living crab species, it inhabits the depths of the Pacific Ocean. In contrast, other members occupy vastly different environments. For instance, the portly spider crab, Libinia emarginata, thrives in the estuarine habitats along the North American east coast, while the great spider crab, Hyas araneus, is found throughout the Atlantic and North Sea regions.

Beyond their physical size and distribution, these crabs display intriguing behavioral patterns. Australian spider crabs, for example, are known for their social stacking behavior, where faster individuals climb over slower ones, creating dense piles. The fossil record also provides glimpses into their history, such as the Priscinachidae family, which is represented by the single species Priscinachus elongatus, discovered in the Cenomanian deposits of France. These varied characteristics highlight the adaptability of the Majoidea, which includes the 'true' spider crabs of the family Majidae, first described by Samouelle in 1819.

The study of these creatures remains a dynamic field, as researchers continue to clarify the boundaries of the superfamily. Whether it is the European spider crab, Maja squinado, or the specialized decorator crabs, each species contributes to our understanding of decapod evolution. By examining both extant species and ancient fossil records, scientists are better able to map the complex history of these marine arthropods, ensuring that our classification systems reflect the true diversity found within the world's oceans.

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