The digestive tract is a vital organ system; although their functions are dependent on one another, each organ has a unique structure. While the embryonic origin of the intestinal tract is similar in all vertebrates, its specific morphology varies significantly by species. Most vertebrates have elongated intestines that coil to fit inside the abdomen. In contrast, ancient fish like the skate Leucoraja erinacea exhibit a spiral-shaped intestine that is only a fraction of the animal’s body length. The compact structure is necessary because these fish have restricted abdominal cavity capacity; two large liver lobes required for buoyancy create a space limit within the abdomen. To maintain the high surface area necessary for efficient absorption of nutrients, the intestine’s primary function, the skate intestine features an internal spiral valve that forms during embryonic development. To understand how the skate intestine gets its distinctive shape, I am investigating mechanical forces as a postulated source of biological spiraling. Previous studies have indicated that mechanical forces, such as constraint or compression, play a role in the development of intestinal morphology. For example, constraint forces exerted by smooth muscle are known to contribute to the formation of villi in the chick and mouse. Additionally, previous work in the Theodosiou lab has identified a possible constrictive force surrounding the outer casing of the spiral, which may be a result of muscles differentiating in the outer casing and forming a collar around the forming spiral. To understand the role of mechanical forces in spiral formation, the goal of my research is to characterize the smooth muscle layers present in the skate intestine. Specifically, I am studying when, where, how many, and in what orientation smooth muscle layers differentiate. Immunofluorescence staining for filamentous actin and smooth muscle actin are used to investigate these questions. Results indicate that three different types of smooth muscle emerge in the developing skate intestine, named by their orientation relative to the gut tube: circular, longitudinal, and helical.