ˌplājēˈästəˌmī noun plural
Usage: capitalized
Etymology: New Latin, from plagi- + -stomi
in some especially former classifications : a group of fishes more or less exactly equivalent to Chondrichthyes or more restrictedly an order including the existing sharks and rays as distinguished from the chimaeras and the extinct primitive groups Pleuropterygii and Ichthyotomi — compare selachii