. Text-fig. 46. Filaments from the second gill arch of (a) Neoceralias spinifer; (b) Melanocetns murrayi; (c) Danaphryne sp. (a, X40; B, X20; c, X40.) may be found in Foxton's (1956) paper. Reference to his table 7 will show that in tropical and sub- tropical waters the mean volume of zooplankton between the surface and 150 m. is more than twenty- times that between 1000 and 1500 m. In the Kurile-Kamchatka area, the biomass () of plankton between the surface and 100 m. is about forty times the value measured between 1000 and 2000 m., (and about ninety times greater than that between 200
. Text-fig. 46. Filaments from the second gill arch of (a) Neoceralias spinifer; (b) Melanocetns murrayi; (c) Danaphryne sp. (a, X40; B, X20; c, X40.) may be found in Foxton's (1956) paper. Reference to his table 7 will show that in tropical and sub- tropical waters the mean volume of zooplankton between the surface and 150 m. is more than twenty- times that between 1000 and 1500 m. In the Kurile-Kamchatka area, the biomass () of plankton between the surface and 100 m. is about forty times the value measured between 1000 and 2000 m., (and about ninety times greater than that between 2000 and 4000 m.) (Zenkevitch and Birstein, 1956). Extra data on the biomass of zooplankton in the North-western Pacific are given by Bogorov (1958). In the surface-zone (0-200 m.) the biomass is 1000 or more, while in the 'transition zone' (200-500 m.), which is generally richer in species than the surface-zone, the biomass falls to about 350 Below this comes a 'deep-sea zone' (500-6000 m.) in which the biomass varies from 2-64 to 78 Between 6000 m. and the deep-sea floor the zooplankton-content is less than 1 Finally some indication of the paucity of life in deeper waters is also given by measure- ments of the oxygen consumption and phosphate regeneration (Riley, 1951). Over the Atlantic (between 450 N. and 540 S.) the curves of oxygen consumption () fall sharply below depths ranging from about 250 to 800 m. (see Riley's fig. 25) and Text-fig. 47 of this Report. 1 The Giganturoidea could also be placed in this assemblage. Nearly all the sizeable specimens in the Dana collections have been taken by nets fishing below a depth of 1000 m., and, apart from their large tubular eyes, they have a low level of tissue development, much like that described under the Lyomeri and Ceratioidea. The giganturoids also have very small kidneys.
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