86 



DISCOVERY REPORTS 



Nectopyramis spinosa Sears, 1952. (Plate V, fig. 1.) 

 ? = Hippopodius cuspidatus Moser, 1925. 



During a period of many years I have picked out from 'Discovery' catches three very curious 

 Prayid nectophores, which I think may be what Moser (1925) described and rather inadequately 

 figured as ? Hippopodius cuspidatus. A fourth was taken in a closing net fished from 1000 to 250 m. 

 by ' Scotia' in 1951 to the west of Ireland in W. long. 17 03', and a fifth also by ' Scotia' in 54 15' N., 

 1 4 32' W. at the same depth. The nectophores are of two kinds, and there are three of the first and 

 two of the second. The first has a very minute obsolescent nectosac (Text-figs. 40 A, B) and the second 

 a much larger functional nectosac (Text-fig. 40 C). In both kinds the radial canals arise separately 

 as in Nectopyramis thetis. 



v^r-s 



~ "iy^Cradd. 



Rbuc Nsobs 



Text-fig. 40. Nectopyramis spinosa Sears. A, dorsal view ; B, lateral view of nectophore of first type, with obsolescent nectosac, 

 'Scotia' 195 1 Cruise, St. 363 ; C, lateral view of nectophore of second type, with functional nectosac, 'Discovery II' St. 1639. 

 *9-5- 



Although there is some variation in the arrangement of spinose ridges in the first group of three 

 nectophores with obsolescent nectosac, there are elements in their arrangement that can be compared 

 with that in the second group of two nectophores with the larger nectosac. For instance we find the 

 same dorsal-median and what I will call ' buccal ' ridge in both groups ; but more material is needed 

 to complete the morphological account. Nectopyramis (including Archisoma) is the only Prayid genus 

 known in which the nectophores bear ridges. 



We may have here, in the existence of two types of nectophore, a phenomenon similar to that 

 found in Amphicaryon, where one nectophore has an obsolescent nectosac. This would be of special 

 interest seeing that other species of Nectopyramis have only one nectophore as far as we know, though 

 presumably their ancestor had more. It is possible that one type of nectophore represents a caducous 

 larval, and the other the definitive nectophore. In favour of this interpretation is the fact that the 

 somatocyst or pallial canal is extended well beyond the obsolescent nectosac in the first group of necto- 

 phores. This extension is characteristic of larval Prayid nectophores. In the second group the pallial 

 canal stops short at the ventral radial canal of the nectosac, just as it does at the pedicular canal in 

 definitive nectophores of Prayids. 



Since I wrote this note Dr Mary Sears has published (1952) a note on this siphonophore, of which 

 ' Dana ' took six specimens — one with the large and five with the obsolescent nectosac. Three were 

 taken in the Indian Ocean, two in the South Pacific and one in the Tropical Atlantic. In none of them 

 were the stem or appendages preserved. Dr Sears regards it as a new species, and in the light of the 



