THE PELAGIAL 



227 



only a small excess of weight in this manner and it is especially effec- 

 tive only for small animals, which have an intrinsically high value of 

 the surface-weight proportion. The simplest means of enlarging the 

 ventral surface lies in the flattening of the body. Leptodiscus, the light- 

 producing flagellate, most Hydromedusae and Scyphomedusae, the 

 turbellarian Haplodiscus, the pelagic nemertines, the crustacean larva 



Fig. 51 



Fig. 52 



Fig. 51. — Hastigerina digitata, a pelagic foraminifer. After Rhumbler. 

 Fig. 52. — Globigerina bulloides, a pelagic foraminifer. After Ziegler. 



Phyllosoma (Fig. 53d), the copepod Sapphirina, and many others are 

 thus flattened. Lateral projections, which may be branched in addi- 

 tion, often occur. Such apparatus is most developed among the radio- 

 larians and Foraminifera, in which the long pseudopodia are supple- 

 mented by spines of the test. Such "suspensory bristles" are notable 

 in Hastigerina (Fig. 51) and Globigerina (Fig. 52). This means of 

 support is less developed among the Metazoa; some of the most 

 conspicuous examples, including annelid worms, their larvae, mollusks, 

 crustaceans, and a fish larva, are shown in Fig. 53. Young transformed 

 starfishes and sea urchins (Fig. 54) have relatively long tentacles and 



