Pterotrachea coronata is a carnivorous gastropod slowly swimming in the open sea all its life. Since P. coronata ingests prey without mastication, the whole bodies of the ingested organisms are often recognizable through the transparent body. The present study described fine structures of epithelial cells along the alimentary canal to elucidate functional adaptations to this digestion mode. The alimentary canal is a simple tube; the epithelial cells lining the tube always have microvilli and are basally underlain by a muscular layer. The structure of the epidermis was different in each organ, i.e., buccal mass, esophagus, intestine, and visceral nucleus, with differences in cell shape, microvilli length and density, and muscle layer thickness. Additionally, a cuticular layer overlies the epithelia in the buccal cavity and the alimentary epithelial cells are multi-ciliated in the visceral nucleus where absorption of digested material and formation of fecal pellets proceed. The long esophagus and intestine of P. coronata are probably suitable to retain ingested materials for the slow digestion process, without mastication. While the intestine occupied most of the alimentary canal, the epithelium was thin and had short, sparse microvilli. This poorly developed but large, transparent intestine in P. coronata is one of the major characteristics of this animal. Slow digestion with retention of prey in the large intestine would be an adaptation for the floating life of this transparent carnivore, allowing it to survive in the epipelagic layers where there are limited chances to obtain prey organisms, especially during the day.