Fig. 1

Development and staging of a Botryllus schlosseri colony. The staging of the animals was performed after Lauzon [63]. The secondary bud develops as thickening of the peribranchial epithelium and the epidermis (stages A1, A2), which evaginates and closes forming a double monolayered vesicle (stages B1, B2). The inner vesicle undergoes morphogenesis and is subdivided into three chambers (stages C1, C2). During “takeover” (stage D), the adult degenerate and get resorbed, the primary buds become adult, the secondary buds become the primary buds and start to bud again a new secondary bud, so a new blastogenetic cycle begins for the next secondary bud (A1) [32, 34]