MARINE BRYOZOA IN THE INDO-PACIFIC REGION 393 



Equatorial Current, together with the Kuro Siwo and the Cahfornia 

 Current, forms the large circulation in the northern half. The South 

 Equatorial Current, derived from the Peruvian Current of the South 

 yVmerican coast, goes westwards to the Papuan coast embracing nume- 

 rous islands of Polynesia on its way. The Indian Ocean is also divided 

 into two parts. The South Equatorial Current, going westwards, reaches 

 the east coast of Africa and bifurcates toward north and south, the 

 southern branch descending along the South African coast. The South- 

 western Monsoon Drift, the extended part of the northern branch, goes 

 eastwards in July and westwards in January. The Malayan Current is 

 derived partly from the North Equatorial Current of the Pacific and 

 partly from the Monsoon Drift of the Indian Ocean, and runs along 

 the Chinese coast up to Japan. 



These facts suggest the probability of the following subdivision of 

 the Region: 1) Pacific coast of America and Hawaii, 2) Polynesia and 

 Australia, 3) Indian coast of Africa, 4) Arabian Sea and Bengal Bay, 

 5) Malay Archipelago and Japan. 



Navigation: The important role of the navigation and the trans- 

 plantation of organisms in the distribution of sessile Bryozoa may be 

 easily recognized. The cosmopolitan distribution of Bugula neritina, 

 Tricellaria occidentalis, Hippothoa hyalina, Watersipora cucullata are 

 adequately explained by their occurrence in fouling organisms. Many 

 of the species exhibit great adaptability to different climatic conditions^ 

 and if transported to distant regions might readily accommodate them- 

 selves to their new environment. 



Water temperature: One of the limiting factors to the physio- 

 logical functions of Bryozoa is the water temperature. The isothermal 

 of 22 °C crossing the middle part of Japan fairly agrees to the northern 

 limit of the Malayan element of Bryozoa. According to our experi- 

 mental study of Watersipora cucullata, the occurrence and settlement 

 of larvae are most active at 18-25°C, and the activity of adult suddenly 

 falls at a temperature lower than 12° C or higher than 28 °C. 



Provinces of the Indo-Pacific Region 

 Taking into consideration the above-mentioned factors that produce 

 predominant influences on the distribution and after making compa- 

 risons among the bryozoan fauna of various parts of the Region, we 

 propose here the following subdivisions of the Indo-Pacific Region on 

 the geological, oceanographical and ecological basis: 

 A. Indian Subregion. 



1 . Ethiopian Province. (East Coast of Africa, Madagascar, Red 

 Sea, Gulf of Aden, Gulf of Persia) 



