Eyed lampreys were identified to species by dentition; ammocoetes, in which developing eyes are covered with skin, were grouped into a single category.
Kostow (1) reported outmigration of Pacific lamprey (often mixtures of ammocoetes and juveniles) during fall, winter, and spring at locations throughout the Columbia River basin.
This information is especially needed to avoid misidentification of early life stages of lampreys in the field (Mesa and Copeland, 2009), given the often incorrect assumption that all juvenile lampreys are Pacific lamprey (Kostow (1); Mesa and Copeland, 2009) and the difficulties of identifying small ammocoetes to species (Goodman et al.
Morphological diagnosis of Entosphenus and Lampetra ammocoetes (Petromyzontidae), in Washington, Oregon, and California.
Like most lampreys (family Petromyzontidae), both of these species have complex life cycles that include an extended larval stage (the ammocoete stage) and a relatively brief adult stage (Hardisty, 2006).