Invertebrate Gallery of the Indian Museum. 31 



or gonozooids), while the others are specially modified to 

 perform only nut:itive functions (nutritive zooids or gas- 

 trozooids). 



The Antipatharia usually encrust rocky bottoms at 

 moderate depths, — 30-60 fathoms. The few deep-sea forms 

 are also rock livers. 



b. ANTHOZOA ALCYONIOMORPHA. 



[Cases 4—6]. 



This sub-Class consists of marine reef-living animals 

 very commonly in the form of branching tree-like colo- 

 nies or of encrusting moss-like or fungus-like colonies, 

 the constituent units or " persons" of which have the typical 

 polyp shape and structure. 



Each polyp usually has eight tentacles, instead of six 

 or a multiple of six tentacles, as in the Actiniomorpha. 

 The possession of eight tentacles and eight septa is in short 

 the principal constar^i, character of the Alcyoniomorpha. 

 The tentacles, moreover, are pinnate. 



The Alcyoniomorpha, like most of the Actiniomorpha^ 

 secrete a firm supporting skeleton or coral, which, however, 

 differs from that of the Actiniomorpha, not merely in 

 being less stony and rigid, but often in important points 

 of development. 



The skeleton or "coral" of the Alcyoniomorpha (i) 

 is sometimes formed entirely by the mesoderm, in which 

 calcareous spicules are deposited to finally fuse together 

 into a hard solid wall : such a mesodermal coral is seen in 

 the specimens of Tubipora musica (the organ-pipe coral) 

 and of Telesto arborea ; but (2) is most often formed by 

 both ectoderm and mesoderm, the mesodermal element, 

 however, greatly preponderating. la this case the polyp, 

 at the point where it attaches itself to the ground, secretes 

 between its ectoderm or outside layer and the ground a 

 layer of horny matter, and as the polyp-stalk grows up- 

 wards this horny mass follows, until it forms a central 

 horny core or axis which follows the polyp-stalk in all its 



