SYSTEMATIC AND BIOLOGICAL ACCOUNT m 



by side in the Red Sea with L. subtiloides, but can at once be distinguished by the fact that there is 

 practically no stalk to its relatively shorter somatocyst. 



Lensia challenged sp.n. 



Thirty anterior nectophores of what appears to be a distinct new species of Lensia were taken by 

 Surgeon Lt. D. O. Haines, R.N. in H.M.S. 'Challenger' (Cdr. G. S. Ritchie, D.S.C., R.N.) off the 

 coast of Southern California on 21 October 1950 at Station 104, 23° 51' N, 112 59' W. The species 

 occurred also at Stations 103, 105, 106, 107, 108, 109 and 114, the first being in 2i°4i' N., iii°43' W., 

 and the last in 31 12' N., 117 31' W. At all these stations the specimens were in a layer of presumed 

 plankton located by echo-sounding. Temperatures in the layer varied from 57 to 61 ° F., and the 

 depths from 37 to 220 m. At night the presumed plankton layer was observed to remain at about 

 37-55 m. as seen on the echo-sounding recorder and by day the layer was occasionally seen on the 

 trace at about 274 m. A number of bathythermograph temperature/depth records taken at the time 

 all show a similar pattern — 80-67 F. at the surface, a degree or so less at 27-5 m., 56-5-62° (once 72°) 

 at 56 m. and 49-5-56° at 131 m. 



Captures of Lensia challenged sp.n., by H.M.S. 'Challenger' in the E/S layer of plankton off 

 S. California in October 195 1 are given in the following table. It shows the descent before sunrise. 



* The haul at this depth was probably made a few metres above the E/S layer. 



Commander Ritchie (1952) stated that migrations appear to depend on light, and not on various depth/ 

 temperature changes, though Moore (1943) makes the generalization that among Siphonophores there 

 is a tendency in the Florida Current for a change in day level in relation to temperature, the animals 

 there moving upward when cold water comes closer to the surface. Herdman (1953) too shows that 

 there appears to be a certain measure of agreement between the depths at which temperature-dis- 

 continuities occur and those of the various echoes recorded. But he adds that it is a matter of con- 

 jecture whether this connexion depends entirely on the purely physical boundaries, or on possible 

 concentrations of falling detritus or animal life checked in its fall by a sudden change in density. 

 According to Cdr. Ritchie the rate of change of depth for descent averaged about 4-26 m. per minute, the 

 movement being very regular over five days. The ascent in the evening was more ragged, small groups 

 sometimes appearing to come up ahead of others, and speeds of ascent varied from 2-74 to 0-91 m. per 

 minute. Open plankton nets were lowered into the mid-level of the E/S layer at night. No fish were 

 caught, and the fine ' texture ' of the echo-sounding record obtained led Cdr. Ritchie to believe that the 

 echoes came from a vast layer of plankton rather than from fish feeding upon that plankton. 



Lensia challengeri bears some resemblances to both L.fowleri Bigelow and L. hardy Totton. From 

 L.fowleri it can be distinguished by a projection, shaped like the peak of a cap, that is found on the 

 baso-dorsal margin of the anterior nectophore, which has the appearance in lateral view of a dorsal 



