Entry 1 sense Webster, 1913 Leptostraca /(lĕp*tŏs"trȧ*kȧ)/ · Lep·tos·tra·ca · IPA 01 n. pl. An order of Crustacea, including Nebalia and allied forms. 1. An order of Crustacea, including Nebalia and allied forms.(Zool.)