English Etymology From translingual Hydrozoa + -an. Noun hydrozoan (plural hydrozoa or hydrozoans) Any of many colonial coelenterates, of the class Hydrozoa, including the hydras, hydroids, hydrocorals, and siphonophores. Translations colonial coelenterates of the class Hydrozoa Catalan: hidrozou m Chinese: Mandarin: 水螅蟲類 / 水螅虫类 (shuǐxī chónglèi) Finnish: polyyppieläin (fi) Japanese: ヒドロ虫類 (hidorochūrui) Polish: stułbiopław m Russian: гидрозо́й (ru) m (gidrozój) Wikiwand - on Seamless Wikipedia browsing. On steroids.