Mesenterial Arrangement: The mesenteries are arranged in pairs, each consisting of two mesenteries adjacent to one another. For the most part, partners of the ordinary pairs are equally developed, but they may be of different size. The arrangement of the pairs may be six-rayed (hexamerous), eight-rayed (octamerous) or ten-rayed (decamerous) (Carlgren, 1949; p. 8). Mesenteries can be classed as incomplete (imperfect) or complete (perfect).