Fig. 4

Remodeling of body cavities during metamorphosis of Phoronopsis harmeri. Histological sagittal sections of animals at consecutive stages of metamorphosis. Color code: red – blastocoel, which partly gives rise to the blood system; cyan – protocoel; blue – mesocoel; green – metacoel. a First step of metamorphosis: larva with everted metasomal sac. Stage about 1 min after the onset of metamorphosis. Larval apical organ is at the right; telotroch is at the left; metasomal sac is to the down. b Stage of eating of the preoral lobe; about 10 min after the onset of metamorphosis. Degenerated apical organ is well visible at this stage. c Stage of eating of the postoral ciliated band: stage about 12–15 min after the onset of metamorphosis. d 9-day-old juvenile completely acquired definitive body plan. Abbreviations: ao – apical organ; bc – blastocoel; c1 – protocoel; c2 – mesocoel; c3 – metacoel; es – esophagus; lv – lophophoral blood vessel; m – mouth; mg – midgut; mv – median blood vessel; pl – preoral lobe; pr – proctodaeum; st – stomach; tt – telotroch; vv – ventral vessel