76 



INVERTEBRATE ANIMALS. 



CHAPTEE VIII. 



SUB-CLASSES LUCEENARIDA, GRAPTOLITID^, 

 AND HYDROCOEALMN^. 



Sub-class Ltjcernarida. 



The next group of the living Hydrozoa is that of the Lucemarida, 

 under which name are included a con- 

 siderable number of forms, differing from 

 one another to a great extent in external 

 appearance. It will be sufflcient here to 

 describe one or two typical forms. 



One group of the Lncernarida is repre- 

 sented by Luaernaria itself (fig. 41), in 

 which there is a cup-shaped body of a 

 more or less gelatinous consistence, usu- 

 ally attached by its smaller extremity 

 to sea- weeds, this end of the body being 

 developed into a small sucker. Like the 

 Hydra, however, Lucernaria is not fixed, 

 but can detach itself at will, and can even 

 swim freely by means of the alternate 

 contraction and expansion of the cup- 

 shaped body (or "umbrella," as it is 

 termed). Round the margin of the cup 

 are tufts of short tentacular processes, 

 and in its centre is fixed a single polypite, 

 furnished with a four-lobed mouth. The 

 essential elements of reproduction are de- 

 veloped within the body of Lucernaria 

 itself, and it does not give off any genera- 

 tive buds, as so commonly occurs in other 

 forms. 

 Another type of the Lncernarida is represented by the organisms 



formerly termed " hidden-eyed " Medusce, and familiarly known as 



Fig. 41. — Two .(specimens of 

 jAlcermiria anrinda attached 

 to a piiif-e of sea-weed (after 

 Johnston). 



