Figure 2

Serotonin-like immunoreactive nervous system in Phoronopsis harmeri during the first stages of metamorphosis. (A-G) Animals at one of the first stages of metamorphosis (the “hood-eating stage”). (H-J) Animals at the stage when the postoral ciliated band is ingested. In all images, the apical is at the top, and the oral side is to the right. Z-projections (B, D, E, G, H) of animals after mono- and double staining for serotonin (yellow) and phalloidin (blue). (A) Whole animal viewed from the top; SEM. (B) Anterior portion of the body. The intertentacular branches are indicated by opened arrowheads. (C) Sagittal semithin section of the anterior portion of the body. (D) Optical sagittal section of the anterior part of the body. The serotonin-like immunoreactive cells in the esophagus are indicated by closed arrowheads. The nerve ring around the anus is indicated by arrows. (E) The portion of tentacular (main) nerve ring with intertentacular branches (arrowheads). (F) Middle part of the body with nerve plexus and nonsensory perikarya (double close arrowheads). (G) Whole anterior part of the body. (H) Anterior part of the body; SEM. (I) Whole anterior part of the animal. The main nerve ring is indicated by double arrowheads. (J) Part of the main nerve ring and lateroabfrontal neurites. The intertentacular branches are indicated by open arrowheads. Abbreviations: ao – apical organ; bc – blastocoel; c3 – trunk coelom; es – esophagus; gp – groups of perikarya; m – mouth; la – lateroabfrontal neurite bundles; of – oral field; p – proctodaeum; pl – preoral lobe; po – postoral ciliated band; pp – remnant of the hood; pt – posterior part of the larval body with the telotroch; sg – neurites of the second group; st – stomach; t – tentacle; tn – tentacular (main) nerve ring; tt – telotroch; yt – youngest tentacles.