84 U.S. NATIONAL MUSEUM BULLETIN 291 



and Weed were unable to correlate differences in gill area in Scofelog- 

 gadus with depth of capture. However, there was a correlation between 

 gill size and the oxygen content in the areas where the subspecies live. 

 Oxygen concentration in the Sargasso Sea habitat of S. m. mizolepis 

 with short, filaments is relatively high, ranging 3-6 ml/L, while the 

 oxygen content of the eastern tropical Pacific habitat of S. m.. hispino- 

 osus with long filaments is very low, from less than 0.1 to 2 ml/L; 

 much of the 200-2000 m depth range of S. m. hlspinosus corresponds to 

 the oxygen minimum layer. Specimens of another melamphaid, Poro- 

 mitra megalops^ also from the oxygen-poor tropical eastern Pacific, 

 have a greater gill surface area than do specimens from the North 

 Atlantic. Ebeling and Weed suggested that the increase in gill surface 

 is an adaptation toward more efficient utilization of oxygen in regions 

 of low oxygen concentration. 



An interesting parallel exists between Scoiyelogadus and Bathyteu- 

 fhis. B. hacidifera has gills with greater dimensions and more filaments 

 than ahyssicola. The only specimens of hacidifera that are available to 

 this study come from the eastern tropical Pacific within the boundaries 

 of the oxygen-poor eastern Pacific Equatorial Water Mass. Oxygen 

 concentrations were determined at each station so an accurate estimate 

 of oxygen values at depths of capture is available (Table VII). The 

 oxygen values range from 0.47 ml/L at 750 m to 1.47 ml/L at 1550 m, 

 and they correspond to the midportion of the oxygen minimum layer 

 which has its lowest values somewhat shallower (200-700 m). Large 

 gill size in hacidifera^ therefore, may well be an adaptation to these 

 very low oxygen concentrations. 



The various populations of abyssicola show differences in gill size 

 also. B. abyssicola has the smallest gills in the Antarctic ; it has larger 

 gills in the eastern Pacific; it has intermediate-sized gills in the At- 

 lantic. Oxygen content of Antarctic waters is very high, ranging from 

 4.0 to 5.0 ml/L in the depth range that abyssicola inhabits; oxygen 



Table VII. — Oxygen, temperature, salinity, and sigma-t values at Bathyteuthis 

 stations in the eastern tropical Pacific (circa 07° N 80° W) 



