CHAPTER 6 



The plaiihtoiiic larvae 



The survival of the results of reproduction, whether they are seeds, eggs 

 or youngsters is all important in maintaining the species, and the dispersal 

 of large numhers in the hopes that at least some will find favourable con- 

 ditions is one of the ways of ensuring this. In the sea what better means of 

 dispersal are there than the movements of the water itself, especially as 

 life there can be a prolonged one because the environment is already ade- 

 quately provided with a good food supply? A planktonic stage in the life 

 history of so many marine organisms is thus to be expected and indeed is 

 found over a wide range, from the spores of the attached seaweeds to the 

 eggs and larvae of the fish themselves. In this chapter some of this great 

 variety of forms will be considered, but the fish will be dealt with in 

 Chapter 7. 



The spores of the major seaweeds are liberated into the sea and form, 

 for the time being, part of the nanoplankton (p. 30) and would be 

 assessed as such in any estimation of productivity. They would, of course, 

 be far more abundant in inshore than in offshore waters but only their life 

 history would readily separate them from the true planktonic flagellates, 

 because they settle down to grow into seaweeds whereas the true flagellates 

 continue to reproduce as such. 



There are marine representatives of almost every class of invertebrate 

 living attached or freely moving on the bottom. To describe all their 

 planktonic larvae is far beyond the scope of this book, and indeed as yet 

 beyond the scope of any marine biologist for the details of so many of 

 them are still unknown. We can, within limits, make sensible comparisons 

 and so make guesses about the kind of larvae some adults will have; 

 we find larvae of these kinds in the plankton which we cannot yet link 

 with certainty to an adult. Sometimes because of times of spawning and 

 the localities in which they are found we can guess which arc which, but 

 often the overlap is too big. It is only a question of time until someone has 

 the opportunity to breed them in aquaria and publish the results, and indeed 

 it is amazing how many thousands of species have already been associated 

 with their larvae — but there are plenty of others yet to be done. 



A glance through the figures illustrating this chapter will give an idea of 

 the range of forms found, and an idea of the types of larvae belonging to 

 the different classes. The text will merely be devoted to certain aspects of 

 interest and will not attempt any descriptions aimed at specific separations. 



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