Occlusor muscle - its double origin (i.) is derived from the is shown.
The posterior occlusor muscles lie in a special closed space which Blochmann also regards as coelomic. The posterior end of the intestine is similarly surrounded by a closed coelomic space known as the peri-anal sinus in which the rectum lies freely, unsupported by mesenteries.
Anterior occlusor muscle.
Posterior occlusor muscle.
The operculum of the normal zooecium has become the mandible, while the occlusor muscles have become enormous.