YOUNG: VERTICAL DISTRIBUTION AND PHOTOSENSITIVK VESICLES 



narrower string of tiny vesicles extends ventrally 

 around the eyes and joins a rather large but ex- 

 tremely thin, loosely associated group of vesicles 

 that lies over the lateral base of the funnel. 



DISCUSSION 

 Vertical Distribution 



The numbers of cephalopod species taken in 

 different 100-m depth zones for the upper 1,400 m 

 showed a broad peak between 500 and 800 m dur- 

 ing the day (Figure 49). An abrupt increase in the 

 number of species near 400 m was obscured by the 

 method of analysis: eight species occurred for the 

 first time between depths of 375 and 450 m. To 

 indicate faunal change, the number of species 

 found for the first time in each zone (i.e., depth 

 zones containing species upper range limits) were 

 compared with zones where species found in lesser 

 depths were absent for the first time (i.e., depth 

 zones immediately below the lower range limits) 

 (Figure 49). 



The peak at 700-800 m in the summed plot of 

 species added and species lost indicates that many 

 species dropped out in the 600-700 m zone and 

 many were added in the 700-800 m zone. The chart 

 also indicates that only two species were encoun- 



tered for the first time at 800 m or below. One was 

 the poorly sampled Brachioteuthis sp. and the 

 other was deep-living Vampyroteuthis infernalis. 

 The data indicate peak species richness in the 

 upper few hundred meters with relatively little 

 change between 300 and 1,000 m during the night 

 (Figure 49). 



Numbers of individuals in different depth zones 

 in the upper 1,400 m (exclusive of young individu- 

 als, captures in oblique tows, and contaminants) 

 were also examined (Figure 50). During the day, 

 the greatest abundance of individuals occurred 

 between 400 and 700 m. This peak reflects the 

 dominance of the enoploteuthids, especially 

 Pyroteuthis and Pterygioteuthis spp. The high rate 

 of capture in the 300- to 400-m zone was due in 

 part to a few species whose upper limits extended 

 slightly above 400 m. Nevertheless, an abrupt in- 

 crease in number occurred in the 400- to 500-m 

 zone. The rates of capture below 1,000 m were 

 unreliable due to the small amount of trawling. 



The night data in the upper 400 m were lumped 

 into 50-m increments due to greater control over 

 trawling depths in near-surface waters. The 

 largest catches at night were made in the upper 

 200 m. In this region two peaks were apparent 

 (Figure 50). The peak in the 50- to 100-m zone was 

 largely due to Pterygioteuthis microlampas, the 



NO A NO L A«L TOTAL NO 



NIGHT 

 NO A NO L A' L TOTAL NO 



E 600 



200 



E- 500 



10 10 20 20 



NO SPECIES 



10 10 10 20 



NO SPECIES 



Figure 49. — Numbers of species versus depth. The histograms 

 were based on species ranges from midwater trawl data. Data 

 were lumped into 100-m depth increments and were not cor- 

 rected for unequal trawling times at different depths. Data for 

 some species were very meager. Young stages found in near- 

 surface waters that can be distinguished by an abrupt change in 

 habitat or by a metamorphosis have been eliminated from the 

 figures. No. A — number of species added (i.e., found for the first 

 time in a given depth zone). No. L. — number of species lost (i.e., 

 absent from a given depth zone but present in the shallower 

 zone). A + L — sum of two previous histograms. Total No. — total 

 number of species in each depth zone. 



-1 — I — I — I — ' — I 

 40 80 120 40 80 120 

 NO. SPECIMENS/ 1000 MIN. TRAWLING 



Figure 50.— Total catch rate of numbers of cephalopod speci- 

 mens from both trawls. 



609 



