88 HISTORY OF THE OCEANS 



how the majority of described organisms should be classified. It is 

 reasonable to assume with Dougherty and Allen (1959) that the 

 red algae are the most primitive group of higher organisms, and 

 that the Cryptomonadineae relate them to the rest of the Protista. 

 From some ancestral unicellular biflagellate that must have been 

 near the ancestor of the existing Chrysomonadina a large number 

 of lines have presumably radiated, giving rise to the brown algae, 

 dinoflagellates, diatoms, aquatic fungi, and through the zoo- 

 flagellate groups, the animal protista. From some group or groups 

 in the last the multicellular animal forms have originated. The 

 green algae and all the terrestrial green plants presumably come 

 from isokont green flagellates whose relationship with the other 

 plant flagellate groups is problematical. 



When we consider the various lines, or to use Huxley's con- 

 venient term, clades of the higher organisms, from the standpoint 

 of what I have termed evolutionary euryhalinity, the results are 

 striking and very interesting. 



In the red algae, in the lower class, the Bangioideae, and in the 

 Nemalionales, the lowest order of the higher class of Florideae, we 

 find a mixture of salt water, freshwater, and euryhaline forms 

 living both in water and soils. In the higher orders of the Florideae, 

 with the single exception of one or two members of the genus 

 Hildenhrantia, all the species are marine. The lower red algae are 

 thus ecologically comparable to the Monera in exhibiting con- 

 siderable evolutionary euryhalinity, whereas practically all the 

 higher forms are stenohaline. 



In the Cryptomonadineae there is evidently much evolutionary 

 euryhalinity. Rhodomonas has both fresh and salt water species. 

 The same is true of the motile Chrysophyceae. From somewhere 

 near the latter the brown algae must have evolved, and in so 

 doing followed the pattern set by the red. The lowest order, the 

 Ectocarpales, have both marine and freshwater members, but all 

 the higher forms are marine. Much evolutionary euryhalinity is 

 retained by many genera of diatoms, but others have become 

 specialized to particular ranges of chemical composition, salt or 

 fresh, acid or alkaline. The Dinoflagellates are largely but of 

 course not exclusively marine ; they seem to spring from a primitive 



