Fig. 14

Ultrastructural details of the lining of meso- and metacoel during metamorphosis of Phoronopsis harmeri. Sagittal thin sections. First stage of metamorphosis (A, F); juvenile in 15 min after metamorphosis start (B); 1-h-old juvenile (D); 4-day-old juvenile (C, E, G). a Proliferating cell (cc) of coelomic lining. Well developed larval muscles (mc) are retained. b Presence of subperitoneal neurites (pn), which contain dense-core synaptic vesicles, under the mesocoel lining (lc2). c Completely established mesocoel lining. d Degenerated muscle cells (dnc) within cells of the mesocoel lining. e Degenerated muscle cells (dnc) within cells of the metacoel lining. f Metacoel lining: myoepithelial cells form long basal projections, which are covered by thick basal lamina (bl). g Somatopleura of the juvenile consists of myoepithelial cells, which form circular musculature (cm). Abbreviations: bc – blastocoel; bb – basal body; c2 – mesocoel; c3 – metacoel; ECM – extracellular matrix; emc – muscle cells, which form musculature of esophagus; mf – myofilaments; rer – rough endoplasmic reticulum; te – epidermis of tentacle