Figure 9

Histology and fine structure of the 1 gill slit stage of Saccoglossus kowalevskii (~ 132 h pf). (A) Slightly oblique sagittal section displaying the opening of the mouth (mo) and the left gill pore (gp). (B) Pharyngeal lining cells. Inset: The slender microvilli (mv) produce a glycokalyx (gx) covering the cells. (C) Duct of the gill pore. Cilia (ci) and microvilli are projecting into the lumen of the duct. (D) High mag of the apical cell surfaces of the cells lining the intestinal region. The entire surface area is enlarged to form microvilli. E The cells lining the duct of the gill pores are interconnected by zonulae adherentes (za). The apical cytoplasm contains numerous centrioles (ct). Inset: The duct lining cells are developing into multicilated cells. (F) The proximal (pmt) and distal (dmt) cells of the metacoel constitute flattened epithelial cells. (G) Epithelial cells constituting the mesocoelic lining. (H) Cross section of the mesocoelic lining cells (msc). Blood vessels (bv) are situated between the basement membranes (arrowheads, bm). Inset: The mesocoelic cells contain myofilaments (myo) within the very basal portions of the cytoplasm. P ac accessory centriole, cr ciliary rootlet, ep epidermis, i intestine, lu lumen, mi mitochondrion, ms mesocoel, mt metacoel, nn nerve net, nu nucleus, pc protocoel, ph pharynx, yo yolk.