STYLASTERINA. 



All the recent genera of this order whose anatomy has been adequately investigated 

 are closely related and may justly be included in one family the Sty laster idae. The only genus 

 that is at all divergent is Steganopora described in this monograph, but as our knowledge of 

 its anatomy is still very incomplete it may provisionnally be included in the same family. 



The characters of the order may be summarised as follows : 



Order STYLASTERINA. 



Hydrophytum arborescent, perforated to a considerable depth by the gastrozooids, 

 dactylozooids and nutritive canals of the living colony. Gastropores usually provided with a 

 conical calcareous projection at the base called the "style". Nematocysts of two kinds, large 

 and small but quite distinct in character from the nematocysts of Millepora. Dactylozooids 

 devoid of tentacles, with solid scalariform endoderm. Gonophores enclosed in ampullae. Female 

 gonads provided with a special nutritive organ the trophodisc. Ova large and centrolecithal. 

 Embryos escape from the ampullae in the form of solid planulae (sterrulae). 



The description given above is modified and abbreviated from that given by Moseley. 

 A few comments are necessary to explain the changes that have been made. In Millepora the 

 living parts of the coral are confined to a very thin lamina at the surface, and to this there 

 is no exception. In the Stylasterina on the other hand the living nutritive canals usually penetrate 

 to the axis of the smaller branches and it is only the main stem and some of the older 

 branches that show any dead supporting coral. The only exception to this general rule is to 

 be found in Sporadopora, in which genus, according to Moseley, "only a comparatively thin 

 layer on the surface of the coral is occupied by living soft structures". A reference to Moseley's 

 description and figure shows however that this layer must be relatively much thicker than it 

 is in Millepora and the difference between the Stylasterina and Milleporina in this respect is 

 a very real one. 



The structure of the nematocysts is an important one in the consideration of the affinities 

 of Coelenterata, because they are organs which show very little variation within the limits 

 of a species. 



