Fig. 1

Diagram of developmental stages of P. californiensis. a Invagination stage, covered with large epidermal cells. b Late-invagination stage, in which anterior invaginations have bifurcated. c Early-rudiment stage. d Late-rudiment stage, in which epidermal cells are shed in chains. e Vermicular stage. ap apical organ, pb proboscis, gt gut, pc posterior cirrus, ai anterior invagination, pi posterior invagination, cg cerebral ganglia, oc ocellus, lnc lateral nerve cord. a′–eʹ Confocal projections of phalloidin-labeled larvae modified from Hiebert et al. [13]. a′ A 30-μm-thick sub-stack of frontal sections of invagination-stage larva. b′ A 29-μm-thick sub-stack of frontal sections of late-invagination-stage larva. c′ A 15-μm frontal sub-stack of an early-rudiment-stage larva. d′ A 5-μm sub-stack of frontal sections of a late-rudiment-stage larva. e′ An 8-μm sub-stack of frontal sections of a vermicular-stage larva. Scale bars 25 µm.