bipinnarial UK /ˌbaɪ.pɪˈnɛəɹi.əl/US /ˌbaɪ.pɪˈnɛɹi.əl/ adjective1 •Relating to bipinnariaExpression was then evident in the tips of archenterons of the gastrulae and then in coelomic pouches until the late bipinnarial stage was attained (Fig 2L–2N ). — 2016