Marginal Sphincter Muscle: The circular muscles of the column may be accumulated at or near the margin and form a sphincter which either is endodermal or mesogloeal . In certain anemones, there is a transition between them, an endo-mesodermal or meso-endodermal sphincter. The primary function of this muscle is to draw the margin inwards over the tentacles during retraction (Stephenson 1928)

Sphincter Muscle Formation: Mesogleal or Endodermal

Images of Various Sphincters: (species names are linked to the Hexacorallian database)

Species: Aulactinia incubans Caption: Cross sections of circumscribed, endodermal sphincter muscles of Aulactinia incubans. (a) Palmate form; (b) pinnate form.	Species: Sagartia nutrix Caption. Cross-section of sphincter.
Species: Glyphoperidium bursa Caption: Portion d'une coupe longitudinale du sommet de la colonne, destinée à montrer le sphincter endodermique sectionné en travers.	Species: Actinioides ambonensis Caption: Sphincter.
Species: Epiactis adeliana Caption: Cross section through the sphincter of Epiactis adeliana.	Species: Carcinactis ichikawai Caption: Cross section of mesogloeal sphincter of Carcinactis ichikawai.
Species: Cribrina altifossa Caption: Sphincter of Cribrina altifossa.	Species: Amphianthus armatus Caption: Cross section through the sphincter.
Species: Calliactis algoaënsis Caption: Sphincter.	Species: Stephanauge annularis Caption: Sphincter.