H DISCOVERY REPORTS 



SALINITY TOLERANCE 

 Siphonophores evidently have a wide range of salinity tolerance as well as of temperature. Although 

 Bigelow (191 1 b) found that in the Eastern Tropical Pacific they are an almost negligible factor in the 

 plankton from waters with a salinity less than 35 % , and that they are entirely absent where the salinity 

 is below about 30% , in the Gulf of Aqaba with surface salinities as high as 40-8 % (Deacon, 1952), 

 the records are far from scanty. 



SIPHONOPHORES FROM THE INDIAN OCEAN 



Table 3 gives a list of species from the Indian Ocean. It will be seen from the brief summary of the 

 broad hydrographic conditions in these waters, given below, that in these regions they are living in 

 surroundings very different from those obtaining in the Red Sea and the Gulf of Aqaba. 



The penetration of water of high salinity from the Red Sea can be detected in the Indian Ocean 

 at depths of about 500 m. in latitude 8° N. to depths of 1250 m. in latitude 20 S. 



According to Sverdrup et al. (1946), the southern limit of the Indian Ocean is marked by the 

 sub-tropical convergence in approximately latitude 40 S. To the north it is closed by the land-mass 

 of Asia. The temperatures of the surface layers are uniformly high during the greater part of the 

 year, varying between 25-29 C. In August the south-west monsoon causes upwelling of cold water 

 along the East African and south-east Arabian coasts as far south as the Equator, and in February the 

 north-west monsoon brings about the same phenomenon in the Bay of Bengal. Consequently, lower 

 surface temperatures are met with in these regions in these months. Salinity values also show an 

 annual variation because of these influences, but otherwise have a sub-tropical maximum of 35'4%o. 



Below the surface-layers are three main water masses : 



(1) Indian Ocean Central water, probably formed at the subtropical convergence by sinking, and 

 having temperatures of 8-15 C. and salinities of 34-6-3 5 -5 % . 



(2) Indian Ocean Equatorial water formed by sub-surface mixing, and having temperatures of 

 4-17 C. and salinities of 34 - 9-35 , 25% . 



(3) Deep-water mass below depths of 2000 m. approximately, formed partly by antarctic inter- 

 mediate water (temperature 2-2° C. and salinity 33'8% ) and partly by antarctic bottom water (tem- 

 perature 2-0° C. and salinity 34-8 % ). Their mixing produces deep water in the Indian Ocean of 

 relatively high salinity 3476 % and temperatures about 2-5° C. 



MORPHOLOGY AND RELATIONS OF SIPHONOPHORA 



An outstanding event in the history of siphonophore literature was the publication in 1946 in the 

 Quarterly Journal of Microscopical Science by Walter Garstang of his ' Morphology and Relations 

 of the Siphonophora '. It is indeed, as John Colman has said, an admirable exercise in classical 

 comparative morphology. 1 Try as one will it is difficult to escape from Garstang's main conclusions. 

 ■Written in less than two years as the last of his great papers, it has its roots deep in his personal 

 history. He told me that he could never have tackled the larval development of the big groups 

 Tunicata, Mollusca, Crustacea and Siphonophora had it not been his duty in the early years of the 

 Plymouth Laboratory to make himself familiar with all branches of the Plymouth fauna, both as 

 regards structure and habitat, an experience which taught him to turn easily from one group to another. 

 No doubt Garstang was not familiar with more than a few Siphonophores, alive or preserved, and the 

 paper itself is really a masterly review of the literature. It is very satisfactory for one who has spent 

 more than twenty years making an intensive and fresh study of the Siphonophora, both preserved and 

 alive, to find himself so much in agreement with Garstang's main conclusions. 



1 Personal communication. 



