150 CORALS 



the world, but it has been found also in depths of 20 to 40 

 fathoms off the Maldives.^ 



The Order Stvlasterina. — The second Order of 

 Hydrozoan corals is called the Stylasterina, and it is repre- 

 sented by two common and widely distributed genera — 

 Distichopora and Stylaster — and several others of rarer 

 occurrence. 



As in Millepora, there is a massive corallum of calcium 

 carbonate which is perforated by a plexus of canals, and 

 there are two kinds of pores — the gasteropores and the 

 dactvlopores. In the common genera mentioned above, the 

 coralhuTi can easily be distinguished from that of Mille- 

 pora bv the presence of styles in the gasteropores, and by 

 the absence of tabulae. In some of the deep-sea genera, 

 however, there are no styles, and tabulae are occasionally 

 present in the gasteropores. The style is a little calcareous 

 column, usually covered with minute tubercles and spines, 

 which is situated in the centre of the pores like the columella 

 of a Madreporarian coral (Figs. 71 and 12). 



The gasterozooids of the Stylasterina resemble those of 

 Millepora, except that the endoderm is reflected over the 

 style so as to provide more digestive surface, and each 

 gasterozooid has a mouth and four short tentacles. The 

 dactylozooids, on the other hand, differ very markedly from 

 those of Millepora in being very short, in having no tentacles, 

 and in possessing a scalariform endoderm which entirely 

 blocks up the cavity. The plexus of canals which forms 

 the coenenchym is not so close as it is in Millepora, and the 

 living tissues penetrate much deeper down into the substance 

 of the corallum. The nematocysts are very small and 

 simple in structure, and are confined to the tentacles of the 

 gasterozooids and the ectoderm of the dactylozooids. There 

 are no nematocysts at the surface of the coenenchym. 



The Stylasterina do not produce free-swimming medusae, 

 but the eggs and sperms are formed in ampullae. In each 

 ampulla there may be one or more cups of folded endoderm 

 called the trophodiscs, each of which supports and nourishes 



1 J. Stanley Gardiner, Fauna and Geography of the Maldive and 

 Laccadive Archipelagoes, vol. i. part 3, p. },2^. 



