Classification and Geographic Distribution of Stylodictya-Type Radiolarians

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Abstract
A collection of 485 radiolarian Stylodictya-type shells from 17 surface sediment samples from the equatorial to Antarctic western Pacific Ocean was studied. Comparison of conventional taxonomic criteria used for the identification of the closely related taxa Stylodictya multispina (= S. validispina), S. aculeata, Porodiscus spp. and Stylochlamydium asteriscus with the results of an objective numerical analysis of 11 two-state and quantitative characters suggest that S. multispina and Porodiscus spp. are members of the same taxonomic unit which decreases in abundance from the equator to the Antarctic. S. asteriscus (predominantly warm-water) and S. aculeata (predominantly cold-water) are the other two members of this species group. Morphologic differences between these morphotypes are investigated and defined.