Papers in Marine Biology and Oceanography. Suppl. to vol. } of Deep-Sea Researcn. pp. 239-241. 



Development and metamorphosis of the larva of 

 Agalma elegans (Sars) (Siphonophora Physonectae) 



By A. K. ToTTON 

 British Museum (Natural History) 



Although Fewkes (1885) published a detailed and illustrated account of the holo- 

 blastic segmentation of the eggs of Agalma elegans, and of the subsequent develop- 

 ment of the larva till it surfaces at the age of about seven days, he did not follow its 

 metamorphosis into the adult. He had previously, however, given (1881, pi. IX, 

 Figs. 1, 2) rather inadequate figures of a post-larval Athorybia stage, and a later one 

 that he called the Physophora stage. The last is perhaps better called the '* Necialia " 

 stage, as I have suggested (1954, p. 62). 



Metchnikoff (1874) had, before Fewkes, watched segmenting eggs of this species 

 without figuring them. He also gave an account, though not so good a one as Fewkes, 

 of the development of the larva and the initial stage of its metamorphosis. But it is 

 difficult to interpret Metchnikoff's later figures and to discriminate between the 

 categories of buds that he figured. 



Haeckel (1869) had been the first to describe the development of an Agalmid, 

 after he had artificially raised about 60 larvae (one of them to the 27th day) of Agalma 

 okenii {Crystallodes rigidum) at Lanzarote. He did not recognize the first gastrozooid 

 or protozooid as such. It is labelled " d " (Dotter) and " dc " (Dolterhole) in all his 

 figures, whilst his Magen-polyp (" p ") is really the second gastrozooid. He did not 

 figure a larval tentacle for the protozooid, and I have never seen one either in Agalma 

 okenii. In my Discovery report (1954, p. 66) I noted that the terminal gastrozooid— 

 the primary zooid or protozooid — was smaller in Agalma okenii than its successors, 

 and had a reduced basigaster. On page 69, however, 1 made the erroneous statement 

 that such a protozooid was not formed. The sentence (lines 1 1-14) " The explanation 

 . . . okenii " should be deleted. 



Reduction of the protozooid in Agalma okenii has gone further than in Agalma 

 elegans, whilst evolution of the bracts has progressed, giving the whole bud-colony 



a character of its own. 



Adult specimens of Agalma elegans were not available except on one day during three 

 visits that I have paid to Villefranche, and I was not able to secure any of the very 

 youngest larvae, either by attempts at breeding or in the tow-net; but I did colloci 

 large numbers of post-larvae in various stages of development, and can now complete 

 the account of growth and metamorphosis. 



The fate of the larval bracts of the Athorybia-V±Q stage has been unknown. Gar- 

 STANG (1946) several times suggested that they are dropped at metamorphosis. As a 

 fact they, or at any rate the last-developed ones, are retained through life in their 

 original very restricted position surrounding the proximal sides of the first and second 

 gastrozooids to appear, where they can be seen figured by Fewkes (1881, pi. IX. Fig. 1) 

 and by Totton (1954, frontispiece. Figs. A, D). But because of the secondary elonga- 

 tion of the area between the budding zone (blastocrene) of the siphosome and the 



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