Length of Pelagic Larval Life in Marine Bottom 

 Invertebrates as Related to Larval 

 Transport by Ocean Currents 



GUNNAR THORSON 



Marine Biological Laboratory, Elsinore, Denmark 



IN 1904 Professor J. Stanley Gardiner published a most stimu- 

 lating little paper on the distribution of larvae of marine animals 

 in which he discussed the duration of pelagic larval life within 

 different animal groups and the velocity of the surface currents, 

 by which they might be transported over the oceans. He suggested 

 that there are no barriers for many crustacean larvae. He estimated 

 the maximum regular passage of larval echinoderms and entero- 

 pneusts at about 20 days, while for sipunculids, annelids, and 

 molluscs it is progressively less, not more than 4 to 5 days for 

 Miiller's larvae and "regular planulae" and probably much less in 

 many forms. Gardiner (1904, p. 409) concludes: "that in the 

 present stage of knowledge any consideration of larval distribution 

 is premature and must be inconclusive." 



Gardiner seems to have had only a few data on the duration of 

 pelagic larval life at his disposal. From rearing experiments he 

 indicated a pelagic larval life of 34 and 32 days respectively for the 

 sea urchins Strongylocentrotus and Echinus. These are the only 

 figures he gave. If Gardiner had examined all the literature 

 published up to 1904, he might have found figures for the duration 

 of pelagic larval life for 1 polychaete, 1 asteroid, 3 echinoids, 1 

 prosobranch, 1 lamellibranch, and 5 decapod crustaceans, i.e., 

 12 species in all. 



Now, 55 years later, there are fairly reliable data on the duration 

 of the pelagic larval life for some 195 species, comprising poly- 

 chaetes, asteroids, ophiurans, echinoids, holothurians, proso- 

 branchs, lamellibranchs, and decapod crustaceans, and perhaps 



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