ABSTRACT
The peripharyngeal coelom of regular echinoids forms five of each of the following: 1) pyramidal-dental cavities with dental sacs, 2) levator-pharyngeal cavities along the pharynx, 3) pyramidal sacs in the peristomial lip cavity, 4) perihaemal-peristomial cavities between the perihaemal tissue (ligament) of the radial canals and peristomial membrane; It also forms one peristomial lip cavity with five large diverticulae, five depressor-pharyngeal cavities along the depressor ligaments and the pharyngeal rods, and five interpyramidal-rotular cavities around the interpyramidal muscles. Diverticulae of the peristomial and pharyngeal lips regulate the openings between the perihaemal-peristomial cavities and the peristomial lip cavity and between perihaemal-peristomial cavities and the pharyngeal cavities. The pharyngeal rods form the oesophageal closure and the circumferential compass muscles form the closure between the haemal system and the pharyngeal-levator cavities (interambulacral).
