Why these strange, clawless crustaceans are the masters of the world's sandy beaches

Nature · Published 3 October 2026 Swipe more like this →

In short: Known as mole crabs or sand crabs, the superfamily Hippoidea has evolved a unique lifestyle. Unlike their decapod relatives, these creatures cannot walk. Instead, they have mastered the art of burrowing into sandy shores across the globe, showcasing a remarkable example of parallel evolution in the marine world.

The Hippoidea superfamily represents a distinct branch within the infraorder Anomura, which also includes hermit crabs, squat lobsters, and the hairy stone crab. Among these four groups, Hippoidea is considered the most basal, meaning it diverged earliest from their common ancestor. While the fossil record for these animals is notably sparse, evidence of their existence stretches back to the Cretaceous period, marking a long history of adaptation to coastal environments.

Physically, members of the family Hippidae are highly specialized for their subterranean life. Their bodies are almost ovoid, and they lack the claws typically found on the first pereiopods of other decapods. Instead of walking, they utilize their legs to dig into the sand with impressive efficiency. Some species have even developed the ability to swim by beating their uropods, a movement pattern that distinguishes them from their crustacean cousins. Their burrowing behavior is so pronounced that it mirrors that of raninid crabs, a striking case of parallel evolution where unrelated groups independently developed similar survival strategies.

Hippoids are found on beaches worldwide, with the notable exception of the polar regions. However, this distribution is not absolute; researchers have discovered larvae of at least one species in Antarctic waters. This discovery is particularly intriguing because the Antarctic lacks the sandy beaches these crabs typically require to thrive. This suggests that while their adult lives are tethered to specific coastal habitats, their larval stages may possess surprising dispersal capabilities, allowing them to traverse environments that would otherwise be inhospitable to the mature, burrowing adults.

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