Bathymetric Distribution of Chaetognaths' ANGELES ALVARINO

THE PRESENT REPORT on the vert ical distribu-tion of the Chaerognarha is based on a study of the collections of plankton made by the Scripps Institution of Oceanography expeditions in the Pacific ( Fig. 1) and Indian oceans. Therefore, all the data included and discussed in this paper have been obtained by the author from studies and analysis of thousands of plankton samples from those oceans; and, when other sources of information are-used in the discussion, the name and date of the corresponding authority and publication are given. The samples studied here that cover the Pacific and Indian oceans were taken at 140 m depth ( oblique hauls), and at other various depths: 270,300, 363,600, 700 or 868 m (closing nets or vertical tows), down to 3000 m deep ( mid-water trawls). The results obtained from these exped itions and from the material examined while studying the seasonal distribution of chaetognaths in the California waters, and also from previous work in the Atlantic, has made it possible to group the species of this phylum into several categories based on their distribution in depth. The correlation between the distribution in depth of the species and the conditions affecting this distribution can only be reached through a knowledge of the two-dimensional distribution of each of the species, the factors.involved in their distributional fluctuations, and the extent to which changes in those factors may affect the distributional pattern. It was found, from these observations, that each individual species of chaerognaths occurs generally at about the same levels throughout the oceans, with the particular exception of Eu-krohnia hamata (Mobius) , as will be shown later in this paper. Therefore, these species can ' Cont ributions from Scripps Institution of Ocean-ography, N ew Series. Manuscript received July 5, 196 2