The lancelet Asymmetron lucayanum complex was collected from subtidal (5–42 m) sandy bottom during a benthic survey designed to describe the biota of Cocos Island National Park (Parque Nacional Isla del Coco), Costa Rica, a World Heritage Site. Taxonomically significant characters of A. lucayanum (number of myotomes, gonads only on the right side of the body, shape of metapleural folds) are discussed. These lancelets were living in poorly sorted and slightly gravelly sand. Although this taxon has a circumtropical distribution, this is the first time it has been collected anywhere in the eastern Pacific.