Figure 12

Histology and fine structure of the juvenile of Saccoglossus kowalevskii at the 2 gill slit stage (~ 432 h pf). (A) Histological section, (B-H) Transmission electron micrographs. (A) Sagittal section showing internal structures. The proboscis stalk is flanked by elongations of the mesocoelic cavity, which are filled with longitudinal muscle strands (lm) completely. (B) Cells lining the roof of the mouth cavity. Glandular mucus cells (glc) are interspersed. (C) Vacuolated cells lining the ventrolateral regions of the anterior pharynx. (D) The stomochord is oval in cross sections and its vacuolated cells surround a central lumen (lu). (E) Horizontal section of the gill pore (gp). The proximal duct of the gill pore is extremely high ciliated. Inset: high mag of the cilia (ci) and their associated basal structures. (F) The intestinal lining is composed of columnar cells. (G,H) special intestinal cells containing zymogen-like granules (zg) or distended amount of rough endoplasmatic reticulum (dER). cr ciliary rootlet, epc epidermal cell, hg hindgut, mo mouth opening, mi mitochondrion, ms mesocoel, mt metacoel, muc mucus cell, mv microvilli, ne neurites, nu nucleus, pc protocoel, ph pharynx, skr skeletal rod, va vacuole, vs vesicles, za zonula adherens.