Nulariidae, Syringoporidae, B, Diagrammatic longitudinal section Tubi oridae and Favosi- of a corallite, showing two platforms, t i dae In the first-named p,and simple and cup-shaped tabulae, t.
In the Tubiporidae the spicules of the proximal part of the body-wall are fused together to form a firm tube, the corallite, into which the distal part of the zooid can be retracted.
The corallites are connected at intervals by horizontal platforms containing solenia, and at the level of each platform the cavity of the corallite is divided by a transverse calcareous partition, either flat or cup-shaped, called a tabula.
- Portion of a colony of Coral- of the corallite, give it the lium rubrum, showing expanded and appearance of a madreporcontracted zooids.
Thus the architecture of the Helioporid colony differs entirely from such forms as Tubipora or Favosites, in which each corallite has its own distinct and proper wall.
As the buds develop the canal system becomes much extended, and calcareous tissue is deposited between the network of canals, the confluent edgezones of mother zooid and bud forming a coenosarc. As the process continues a number of calicles are formed, imbedded in a spongy tissue in which the canals ramify, and it is impossible to say where the theca of one corallite ends and that of another begins.
After division the corallites continue to grow upwards, and their zooids may remain united by a bridge of soft tissue or coenosarc. But in some cases, as they grow farther apart, this continuity is broken, each corallite has its own edge-zone, and internal continuity is also broken by the formation of dissepiments within each calicle, all organic connexion between the two zooids being eventually lost.