Nudibranchia Syllabification: (Nu·di·bran·chi·a)Pronunciation: /ˌn(y)o͞odəˈbraNGkēə/ ZoologyDefinition of Nudibranchia an order of shell-less marine mollusks that comprises the sea slugs. Order Nudibranchia, class Gastropoda Origin:modern Latin (plural), from Latin nudus 'nude' + branchiaNudibranchia in other Oxford dictionaries Definition of Nudibranchia in the British & World English dictionary