80 



U.S. NATIONAL MUSEUM BULLETIN 291 



Number Gill 

 Filaments 



« •> 



* '»o 



<fe 



• B. bacidifcrg 

 B. obYHicola 

 O Antarctic 

 # E. Pocific or Atlonti 



Figure 18. — Number of gill filaments in Bathyteuthis bacidifera and B. abyssicola plotted 



against mantle length. 



increase in number of gill filaments up to about 30 mm ML; above 30 

 mm the points level off at an apparently maximum nmnber of fila- 

 ments (20-23). The three populations of abyssicola overlap in number 

 of gill filaments and are not divisible into separate components. 



The plot for hacidifera rises sharply in the first 12 mm of ML ; be- 

 tween 17 and 37 mm the increase in numbers is gradual, rising from 23 

 to 26 filaments. 



Specimens of hacidifera of 9-12 mm ML have 20-23 filaments; 

 abyssicola, does not attain 20 filaments until a mantle length of about 

 22 mm, and only two specimens had 23 filaments (31 and 55 mm ML). 

 In any size group there is a difference of 2-3 filaments between the 

 minimum number in hacidifera and the maximum in abyssicola. East- 

 ern Pacfiic abyssicola is inseparable from other populations of this 

 species in number of gill filaments, and no apparent overlap of values 

 exists between the two species. 



2. Gill length 



Figure 196 shows gill length against mantle length. The points for 

 abyssicola from the Antarctic fall well below those for hacidifera. 

 while the points for abyssicola from the Atlantic and eastern Pacific 

 lie between these values. Atlantic specimens have gills nearly the same 

 length as Antarctic specimens, but eastern Pacific specimens have gills 

 intermediate in length between Antarctic specimens and bacidifera. 

 Figure 20a plots the mean of the gill length to mantle length indices 

 of the four populations. The gills of Antarctic and Atlantic abyssicola 

 are about one-third as long as the mantle and gills of eastern Pacific 

 abyssicola are just over 40% as long; B. bacidifera has gills nearly 

 one-half as long as the mantle. 



