BATHYPELAGIC SQUID BATHYTEUTHIS 



83 



Table VI. — Gill indices of the populations of B. abyssicola and 

 B. bacidifera ' 



1 The dimensions of gills from B. benyi 16-49 mm in ML are appended here. Gill filaments number 19-21. 

 Indices— OL : ML=43-53 (48.6); GW : ML=7.5-15.7 (12.5); GW : GL=17-30 (25.5). 



2 OL=giU length; GW=gill width; ML=mantle length. 



Significance of GiU Size 



In the order Octopoda the number of gill filaments is commonly 

 used as a taxonomic character, but in the suborder Oegopsida the size 

 of the gills has not previously been examined for taxonomic or biologi- 

 cal significance. Eobson (1925, p. 1337) presented a study of gill size 

 in the deep-sea Octopoda. He showed that, in general, the gills of deep- 

 sea octopods are more or less reduced in area, in number of filaments, 

 and by atrophy of the inner demibranch. Although Robson reached no 

 definite conclusions, he suggested that the reduction in respiratory sur- 

 face in deep-sea octopods was related to lowered metabolism in the low 

 temperatures of the depths. Voss (1967) also considered that reduced 

 gill area is due to reduced metabolic requirements. 



Differences in gill size have been recorded for several groups of meso- 

 pelagic and bathypelagic fishes. Marshall (1960) and Walters (1961) 

 have noted that the surface area of gills in bathypelagic fishes is much 

 less than in mesopelagic species. Three species of the bathypelagic 

 genus GonoHtoina exhibit a trend toward reduction in gill surface with 

 the shallowest living species having the greatest gill area. The sugges- 

 tion for these fislies is that the deeper living species tend to have lower 

 metabolisms and to lead less active lives. Walters considered that the 

 bathypelagic giganturids have a metabolic level about one-third that 

 of coastal fishes. 



Ebeling and Weed (1963) reported a clinal tendency in the length 

 of the gill filaments in three geographically distinct populations of the 

 melamphaid fish, Scopelogadus mizolepis. Gill filaments on the 'first 

 arch of S. m. mlzoleph from the Sargasso Sea were short, those of 8. nn. 

 hispinosus from the Gulf of Panama were long, and those of S. m. 

 mizoleplfi from the Indo-Pacific and off West Africa were intermediate 

 in length. Contrary to Marshall's findings in GonostoTna spp., Ebeling 



