CCELENTERATA — CORALS 



Sub-class 2. Alcyonaria 



135 



Tentacles hollow, pinnate, always eight in number as are 

 likewise the mesenteries. 



A calcareous skeleton is apparently present in all ; it is usually 

 composed of separate spicules which develop in the ectoderm 

 but often pass into the mesogloea. These forms may have in 

 addition a horny skeleton. They occur from the Ordovician to 

 the present. 



Super-order a, Odocoralla 



Usually composite corals ; skeleton calcareous, or horny, or 

 apparently absent (name from Greek odo, eight, in allusion to 

 the eight tentacles). Ordovician to present. 

 Tubipora. Living. 



This red coral is composed of parallel tubes, — the corallites 

 (whence the name from Latin tubus, a tube, + porus, a pore). 

 During the life of the colony each corallite lodges a polyp. The 

 polyps are connected with one another by horizontal platforms 

 which branch out from the level of the tabulae and from which 

 new polyps arise by budding. The skeleton is formed by the 

 union of the spicules scattered throughout the mesogloea. 



1. Sketch (a) top view, (b) side view. Label corallites, 

 platform, solenia tubes. 



2. How do new^ corallites arise in the colony? 



3. What are the solenia? 



Gorgonia. ' Living. 



Compound coral, tree-like, but branching in one plane, and 

 all branches united to their tips by cross branches. The up- 

 bending of the ectoderm of the base forms a branched horny 

 axis extending throughout the colony. The calcareous spicules 

 present in the mesogloea form a coating upon this axis in the dried 

 specimen (whence the name from Latin Gorgonia, Gorgon-like, 

 in allusion to its hardening in the air, just as the Gorgon, or 



