As larvae, horseshoe crabs swim vigorously for hours, but they adopt diurnal activity patterns as juveniles and adults. When resting, horseshoe crabs often bury themselves in shallow burrows. Crawling along the substrate is the primary means of locomotion, but horseshoe crabs sometimes swim upside-down by using the book gills for propulsion. As adults, horseshoe crabs migrate annually from deeper near-shore waters to beaches for spawning. Individuals that are flipped onto their backs use the telson to arch the body and roll over.
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