E, Section through a dividing calicle of Mussa, showing the union of two septa in the plane of division, and the origin of new septa at right angles to them.
When fully extended, the upper part of the zooid projects for some distance out of the calicle, and its wall is reflected for some distance over the lip of the latter, forming a fold of soft tissue extending to a greater or less distance over the theca, and containing in most cases a cavity continuous over the lip of the calicle with the coelenteron.
The whole system of dissepiments in any given calicle is often called endotheca.
Tabulae are stout horizontal partitions traversing the centre of the calicle and dividing it into as many superimposed chambers.
Thus in the family Stauridae there are four chief septa whose inner ends unite in the middle of the calicle to form a false columella, and in the Zaphrentidae there are many instances of an arrangement, such as that depicted in fig.
In this coral the calicle is divided into quadrants by four principal septa, the main septum, counter septum, and two alar septa.
The cavities both of the calices and coenenchymal tubes of Heliopora are closed below by horizontal partitions or tabulae, hence the genus was formerly included in the group Tabulata, and was supposed to belong to the madreporarian corals, both because of its lamellar skeleton, which resembles that of a Ma.drepore, and because each calicle has from twelve to fifteen radial partitions or septa projecting into its cavity.