Patagium is a unique structure found in some spumellarian Radiolaria and has been considered to be a diagnostic criterion at the generic level in the generally accepted scheme of classification. A continuous variation in degree of preservation and (or) developmental stages of this structure from complete to absent has been found in genera such as Hymeniastrum-Dictyastrum and Euchitonia-Rhoparastrum from northeast Pacific Ocean bottom sediments. The study of a rich radiolarian fauna in core samples from Java, Mindanao, and Mariana trenches reveals similar features and indicates that such a complete sequence of variation is neither a rare phenomenon nor biogeographically significant.

The taxonomic value of Patagium, therefore, needs critical reconsideration. The degree of development or preservation of Patagium found in a specimen seems to be unrelated to radiolarian ontogeny, although its real significance can not now be determined.

Fragments of the diatom Ethmodiscus rex (Wallich) Hendey also are found abundantly and consistently in the middle and lower parts of the Mindanao trench subsurface section, whereas only a few sporadic occurrences are found in the Java and Mariana trench samples.

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