FMRF-amide-like and alpha-tubulin-like immunoreactive elements in competent larvae of Phoronopsis harmeri . In all images, the apical is at the top, except in H where the apical is to the upper left corner; the ventral side is to the right (B, C, G, J). Z-projections after mono- and double staining with FMRF-amide (green), phalloidin (blue), and alpha-tubulin (cyan). (A) Whole larva viewed from the right. (B) The part of tentacular neurite bundle (tn) passing under the tentacles and immunoreactive mediofrontal neurite bundle (mf) in the tentacle. (C) The apical organ with two types of perikarya; one type contacts the surface of the epidermis (cp) and the other does not (ncp). (D) The distal part of the median neurite bundle with the enlarged portion (fo) of the median branch. (E) Distal portion of the proctodaeum with the anal nerve ring (open arrowheads). (F) Ventral view of the middle portion of the anterior part of the larva with median neurite bundle (mn) and esophageal neurites (es). (G) Lateral view of the metasomal sac (ms). (H) Ventral view of the anterior portion of the larva stained with alpha-tubulin. (I) Lateral view of the anterior portion of the larva stained for alpha-tubulin. (J) Several tentacles viewed from frontal and lateral sides. (K) The lower part of the stomach (st) and the midgut with immunoreactive perikarya (closed arrowheads) and neurites (nmg). Abbreviations: am – anterior marginal neurite bundle; ao – apical organ; cp – ciliated perikarya; fo – frontal organ (the enlarged portion of the median branch of the median neurite bundle); int – intestine; la – lateroabfrontal neurite bundle in the tentacle; lf – laterofrontal neurite bundle in the tentacle; m – mouth; mn – median neurite bundle; mnr – minor nerve ring; ncp – non-ciliated perikarya; oms – opening of the metasomal sac; pm – posterior marginal neurite bundle; vlb – ventrolateral branch.