SIPHONOPHORA OF THE INDIAN OCEAN 



TOGETHER WITH SYSTEMATIC AND BIOLOGICAL 



NOTES ON RELATED SPECIMENS FROM 



OTHER OCEANS 



By A. K. Totton 



British Museum (Natural History) 

 With a frontispiece, chart, 12 plates, and 83 text-figures 



INTRODUCTION 



The original object of this report, based primarily on the very rich collections made by R.R.S. 

 'Discovery II ', was to investigate the Siphonophore fauna of the Indian Ocean, which, by com- 

 parison with that of the Atlantic and Pacific, was little known. It soon became apparent that, as 

 Bigelow had long suspected, members of the group have very wide distributions, and that it was, 

 indeed, doubtful if any species is either confined to or excluded from some part of the Indian Ocean, 

 except those few species that are confined to antarctic waters. The chief result then of the study of 

 the collections has been to advance our knowledge of the morphology of many of the species con- 

 cerned; and accordingly use has been made, in the systematic account, of some new and critical 

 specimens taken in other waters, not only by ships of the Discovery Committee, but by other 

 expedition ships as well. 



Our knowledge of the Siphonophora does not increase as rapidly as it might, because the systematist 

 can only, with few exceptions, obtain the material needed for study by laboriously picking it out of 

 plankton hauls. Unfortunately man-power is insufficient for sorting. For this reason there are still 

 some thousands of plankton net hauls among the Discovery Collections alone that have not been 

 examined for Siphonophora, all of which are holoplanktonic animals ; no one can tell what treasures 

 these jars of plankton may contain. One may search for a very long time before being lucky enough to 

 find a really well-preserved specimen, or a larval or other much desired stage, of some particular 

 species, especially if it is a deep-water one. Chuniphyes moserae may be cited as an example. The 

 rarely seen Nectopyramis spinosa, N. [Archisoma] natans and the Rhodaliids, of which I have never 

 found a specimen, are others. There is also the inherent difficulty of dealing with fragmentary 

 specimens. Again, many of the species occur in two phases, since the stems of most Calycophores 

 eventually break up into free-swimming groups of buds called eudoxids, the successive gonophores 

 of which in their turn may break away and swim as free medusae. I have been lucky enough to 

 secure, anaesthetize and preserve for comparison with the fragments secured by nets, fairly complete 

 specimens of Forskalia edwardsii, Apolemia uvaria, Agalma elegans, Nanomia bijuga and Stephanomia 

 rubra — all of them available at times at Villefranche, some in large numbers. 



The polygastric stages of Diphyiinae and most of their eudoxids, especially those which occur near 

 the surface, as well as the polygastric and eudoxid stages of the Abylopsinae are now well known. 

 The Prayidae are less well known; also the Physonectae, which are the most difficult to determine 

 because they fall to pieces in the nets or in the bottles of plankton, and no one except Bigelow has 

 had the patience to describe and figure accurately more than a few of the pieces. This is regrettable 

 because the nectophores, bracts, gastrozooids and tentacles, siphons and gonophores, both individually 



