Morphologic analysis of the spiral intestine during development in Leucoraja erinacea

Most vertebrates with high protein diets compensate for the need for large absorptive surface area via long, looped villi covered intestines. In contrast, cartilaginous fish have unique spiral intestines. The spiral structure allows for increased surface area in enclosed, short length of intestine. Spiral intestines are present in all cartilaginous fish, with species specific number of spiral turns. Here, we define the progressive turns (pitch and helical angles) of the spiral during development in little skate, L. erinacea. The spiral begins as a single fold and increases to 8 spiral turns. Using microCT-scanned images of developing embryos, we analyzed the dorsal and ventral pitches of the spiral from developmental stages 25 to 34. Pitch decreases from the rostral to  caudal end of the spiral. To determine the extent the spiral folding varies throughout the gut tube, we measured the helical angles. Parabolic trends appear in earlier stages where the spiral folds are steep near the stomach, decline midway, and incline in the caudal end. At later stages, we observe third degree polynomial trends, with alternating dips and rises of the steepness of the folds, that overall decline down the spiral as the valves’ geometry become more linear.  The characterization of such features of the intestine provides avenues to understanding the morphological changes that occur during development and how a malrotation, as seen in the human gut development, could have detrimental consequences.