order Euphausiacea or·de·reup·hausiacea uncommon noun 1. small commonly luminescent crustaceans; important element of marine plankton: krill SynonymsEuphausiaceaorder Euphausiacea Related words Broader terms animal order Parts Malacostraca Part of krillEuphausia pacifica WordNet 2.1 (Princeton University). WordNet 2.1 Copyright Princeton University. All rights reserved.