The study of the digestive epithelium in Sagitta setosa, S. serratodentata, and S. pacifica revealed only a few morphological and cytological differences among the three species. The gut was divided in two main regions. The first is the cephalic region where the epithelium is composed of three distinct cell types (S1, S2, and S3), the ultrastructure of which is probably specialized either for the synthesis of mucosubstances (S1), or enzymes (S3), or both (S2). The second region of the gut extends to the trunk and is mainly composed of the intestine and a short vertical rectum. No intestinal diverticula were observed. The intestinal epithelium displayed two ciliated cell types, anteriorly, a secretory cell type (S4) containing large mucus-like granules, and a second cell type (A) predominated in the posterior part of the intestine. A-cells appear to have two main functions. Although they exhibit secretory granules, they also display typical endocytotic features in their upper half, i.e. coated vesicles, a well-developed tubulo–vesicular network and two distinct types of digestive vacuoles corresponding to an endosome–lysosome-like system. From the distribution and presumed function of the cells, the gut may be divided in two main functional units, i.e. the cephalic and trunk units.