Fine structure of the coelomic epithelium of Sagitta elegans (Chaetognatha)

Summary The coelomic space in the trunk of the arrow worm Sagitta elegans is lined by a thin epithelium, which may be termed coelomic epithelium. The visceral part of this epithelium is composed of flat cells characterized by thin and thick myofilaments, which constitute the circular musculature of the gut. In addition mitochondria, rough ER, and smooth walled cisterns, as well as vesicular and granular inclusions occur; the apical and basal plasma membranes exhibit no particular specializations. The parietal epithelium is exceedingly thin and covers the muscle cells of the body wall. In the lateral fields columnar ciliated cells are to be found which are rich in rough ER cisterns and which apparently are also coelomic epithelial cells.