When zoologist Terry Gosliner saw a carpet of sea slugs covering the coral rubble of Puerto Galera in the Philippines, he couldn’t believe his eyes. “It was like an underwater Easter egg hunt,” he says. As part of a California Academy of Sciences marine expedition from March to May, Gosliner and his team discovered more than 40 new species of nudibranchs—brightly colored, poisonous sea slugs with frequent applications in biomedical research (shown above). The expedition, a joint American-Filipino effort, found about 100 “likely” new species including barnacles, urchins, and the nudibranchs. At one point, divers—who canvassed everything from shallow coral reefs to the dimly lit depths of the reef’s “twilight zone”—were finding at least 10 unknown species per hour. The Philippines possesses unusual marine biodiversity, Gosliner says, because of the high nutrient content of cold and warm waters that mix in its Verde Island passage. He says most of the new species had never been found before because of technological limitations during past expeditions. The team hopes its discoveries will encourage coral reef preservation in the Philippines by showcasing the richness and utility of the region’s marine life.