Paolo Burighel, Carlo Brena, Gian Bruno Martinucci, Francesca Cima

Invertebrate Biology, 120: 278-293. doi:10.1111/j.1744-7410.2001.tb00038.x

Gut ultrastructure of the appendicularian Oikopleura dioica (Tunicata)

“We propose the following hypothesis for food processing in the alimentary canal. Absorption of material digested by the enzymes of the gastric band begins in the left lobe of the stomach. In the globular cells, endocytosis of macromolecules may occur, followed by intracellular digestion. Absorption continues in the right lobe of the stomach, where the ciliated microvillar cells store material in the form of lipid droplets. In the stomach, food is wrapped in a peritrophic membrane secreted by the epithelium, and fecal pellets form in the vertical intestine. These pellets advance through the intestine, while absorption continues in the ciliated microvillar and rectal globular cells; proteins are stored in the rectum. The gut epithelium might also be involved in ion and liquid transport for absorption and/or osmoregulation of internal fluid.”