We defined three distinct pre-ancestrula stages based on the anatomy of the developing polypide and the overall morphology of pre-ancestrula.
Yue Him Wong, Hao Wang, Timothy Ravasi, Pei-Yuan Qian 2012, 'Involvement of Wnt Signaling Pathways in the Metamorphosis of the Bryozoan Bugulaneritina', PLoS ONE10.1371/journal.pone.0033323. Retrieved from PLOS CC BY 4.0 (https://creativecommons.org/licenses/by-sa/4.0/legalcode)