cumacean /kjuˈmeɪ.ʃən/adjective 1noun 1forms 3 adjective1 •Relating to, characteristic of, or belonging to the Cumacea.From the second sampling campaign, two cumacean species collected at Isla D and polychaetes (suborder Terebellida, family Ampharetidae) were added to the dataset. — 2015 noun1 •Any small marine crustacean of the order Cumacea, closely related to tanaidaceans. formscumaceans · more cumacean · most cumacean