Alveolar Mesogleal Sphincter Muscle: : In cross-section, the mesogleal sphincter muscle of many sea anemones is composed of numerous small, more or less spherical holes surrounded by muscle fibers. A sphincter in which the alveoli are scattered is termed alveolar. When the alveoli are so close together that the reduced strands of mesoglea between them form a network, the sphincter muscle is termed reticular. The distribution of the alveoli can be taxonomically important.