ii8 



THE SEAS 



are noteworthy for possessing solid skeletons on which their 

 protoplasm is supported. Although these skeletons are so 

 minute, they are fashioned m the most beautiful and 

 symmetrical patterns. Almost every conceivable shape is 

 to be found among them, and a few forms from bottom 

 deposits are figured in Plate 21. 



Another unicellular animal that is very commonly found 

 is the Globigerina, which builds a calcareous shell made up of 

 a number of connecting compartments (Plate 21). 



So abundant are these two groups, the Radiolarians and 

 the Globigerinas, in certain parts of the ocean, that when 

 they die their skeletons, sinking 

 to the bottom, form characteristic 

 deposits. These are the Radio- 

 larian and Globigerina Oozes 

 mentioned in Chapter III ; in 

 certain localities also Diatom 

 Oozes are formed from the rain of 

 siliceous frustules, the skeletons 

 of the dead diatoms. 



Enough has been said of the 

 most important members of the 

 animal plankton. Let us now 

 consider some of the more 

 grotesque and unusual forms. 

 Ordinary shellfish or molluscs are heavy lumbering 

 creatures ; yet there are some members of this group of 

 animals that are delicate enough to drift about in the water 

 layers amongst the plankton community without fear of 

 sinking rapidly to the bottota. They are the sea butter- 

 flies, a most fascinating group of marine organisms. 

 Perfectly transparent, some carrying a delicate paper-like 

 shell, they move through the water by the rapid flapping 

 of what appear to be wings. These wings are in reality 



Fig. 23. 

 Pteropods or Sea butterflies. 



1. Creseis acicula. 



2. Clio pyrimadata. 



3. Limacina retroversa. 



