7 4 DISCOVERY REPORTS 



Quite recently, in June 195 1, I was able to identify such larvae of a Hippopodiid and a Prayid from 

 the Antarctic ice-edge. But we know only one Antarctic species of each family, so that after seriation 

 of growth stages we can reasonably assume that these ice-edge larvae are those of Vogtia serrata and 

 Rosacea plicata. These last grow to a considerable size, a diameter of 12 mm. The larvae of Vogtia 

 serrata and Rosacea plicata can be separated by the shape of the somatocysts. Without attempting to 

 go into detail it may be stated that in larvae of R. plicata the somatocyst is ovate or globular, whilst 

 in Vogtia serrata it is elongated. There appears to be a much more pronounced angle in the dorsal 

 wall of the hydroecium of the larval nectophore in Rosacea plicata than in Vogtia serrata. Both have 

 comparatively straight lateral subumbral canals, those of Rosacea plicata being somewhat sigmoid 

 in shape. The post-larva of R. plicata was recorded by Bigelow (19110) as Hippopodius hippopus in 

 his report on Biscayan Siphonophores. I have re-examined some of these ' larvae ' from ' Research ' 

 Station 36K. One is an eudoxid, and three are post-larvae of Rosacea plicata (Text-fig. 32). 



Som 



Cradlat 



Som 



Gz- 



Text-fig. 32. Rosacea plicata. Larva from 'Research' (1900) St. 36^, Bay of Biscay. A, lateral view of whole larva, x6; 

 B, larval nectophore, x 24 ; C, view of nectophore from aboral end, x 22. 



Thanks to the generosity of Dr Tregouboff, Director of the Station Zoologique at Villefranche, 

 where so much of the pioneer work on Siphonophores was carried out, I have been able to examine 

 a very well-preserved post-larva of Vogtia glabra (PI. IV, fig. 2 ; Text-fig. 33). It is identifiable because 

 within the hydroecium of the larval nectophore is a young, definitive, heteromorph nectophore 

 characteristic of the species. 1 Its identification is important because the larval nectosac shows clearly 

 that only dorsal and ventral radial canals are developed at this stage in V. glabra, if my identification 

 is correct. Both types of shed larval nectophores, i.e. with two and with four radial subumbral canals, 

 have been found from time to time in plankton samples, and would constitute distributional records 

 for the species concerned. In Chun's (18886) figures of Naples larvae he omitted the dorsal canal 

 (inserted by Moser in a copy, 1925). 



R.R.S. 'Discovery II' has taken many dozens of post-larvae of Rosacea plicata measuring up to 

 12 mm. in length. There is a clear discontinuity between these and the smallest definitive nectophores. 

 From this fact I deduce that the larval nectophore of R. plicata is caducous, as in Hippopodius. 



Moser (19240) figured larval nectophores of Rosacea cymbiformis, Vogtia serrata and V.pentacantha. 

 The subjects of her plates (pi. 1, fig. 3 ; pi. 11, fig. 5 ; and pi. in, fig. 4) contained a young definitive 

 nectophore, but the last two cannot be identified with much certainty. 



1 Only two prominences are present above the nectosac and not four. In the larva from Orotava, attributed by Chun 

 (i888«) to Hippopodius hippopus, he did not mention the number of prominences, but figured what looked like one of a pair 

 only. But Chun's larva had four radial subumbral canals. 



