246 



MARINE ANIMALS 



annelid Spirorbis. The most frequent hydroids are Clytia and Lao- 

 medea. A small sessile ascidian (Diplosoma) is present. The nudi- 

 branch, Scyllaea pelagica, creeps over the weed, and the weak swim- 

 ming crab, Planes minutus, uses 

 it as a resting place. The Sargasso 

 fish Pterophryne makes a nest 

 among the "leaves" by tying them 

 together with mucus. The weed 

 is yellowish brown, spotted with 

 white by the Membranipora and 

 Spirorbis. Many of the Sargasso 

 animals are similarly white- 

 spotted on a yellowish brown 

 ground color; they may have re- 

 markable weed-like appendages. 

 This is especially true of the fishes 

 (pipefish and sea horse, besides 

 Pterophryne) and the nudibranch, 

 as well as certain crustaceans. 46 

 The enemies against which this 

 coloration may protect them are 

 doubtless the sharp-sighted 

 birds. 43 



A number of unexplained 

 faunal parallels exist between the 

 fauna of this area and that of the 

 Mediterranean, such as similar 

 compositions of the nannoplank- 

 ton, similar radiolarians, with 

 Lithoptera fenestrata known only 

 from these two regions; other 

 species with similar distribution 

 include the annelid Alciopa con- 

 trainii, and the copepod Copilia 

 mediterranea. 



For the rest, the Sargasso Sea 

 is characterized by poverty of 

 plankton. Its water is remarkably clear; the Seechi disk is visible to 

 66 m. depth as compared with 33 m. in the Mediterranean, 20 m. in the 

 North Sea, and 13 m. in the Baltic. Among the few abundant forms 

 are the water flea, Evadne spinijera, and the larvae of the forms 

 living on the weed. The high temperature of the water at considerable 



Fig. 62. — Floating piece of sarga?- 

 sum, covered with the hydroids Aqlao- 

 phenia and Clytia, the bryozoan Mem- 

 branipora, and the tube building worm 



Spirorbis. After Hentschel. 



