Fig. 5

Ultrastructure of putative hemoblasts and other cell types in the Styela plicata intestinal submucosa. a Cell clusters in the submucosa include undifferentiated cells or putative hemoblasts, as well as other cell types in different stages of maturation. The two lateral cells (arrows) show features of undifferentiation or early stages of differentiation, including a euchromatic nuclei, and small cytoplasmic dense granules; whereas the cell in the center presents features of late differentiation, including larger dense vesicles in the cytoplasm and an irregular plasma membrane. b An elongated intestinal glandular cell type with endoplasmic reticulum (ER, white arrows) and mitochondria (m) is shown next to a putative hemoblast with a large nucleus and distinct nucleolus. c Cells at different stages of maturation in the submucosa; one granulocyte is shown (arrow) next to three smaller cells with irregular plasma membranes. d Mucosa shows a pseudostratified columnar arrangement and the cells display electron-dense granules on the apical side (black arrow). e Serosa cells show a cuboidal or squamous shape