The tropico-equatorial species of Chaetognatha and Siphonophorae in the Indian" Ocean and adjacent waters are analysed. Particular attention is devoted to the species composition in the various regions, their abundance, spatial distribution, and to the taxonomic and ecological relationships of sympatric species and with their cognates inhabiting adjacent and farther allopatric localities. These studies will attempt to analyse the relative importance of the species producing centers, and the mechanisms involved in the processes of dispersal, spatial permanence of the populations and zoogeographical boundaries.