Taxonomy and species diversity of holocene pylonioid radiolarians from surface sediments of the Northeastern Indian ocean

Pylonioid radiolarians show high species diversity in surface sediments of the northeastern Indian Ocean. They can be applied as important oceanographic indices in tropical and subtropical oceans, but pylonioid radiolarian identification has presented challenges because of major change in the appearances of specimens in different orientations. Examination of their internal structures for precise identification has been considered, but this method is not realistic for examining thousands pylonioid specimens embedded on microscopic slides. Therefore, we have developed practical methods for pylonioid radiolarian identification under transmitted light microscopy with mounted slides. This procedure begins with confirming the orientations of specimens with respect to the shadow of the central combination. After orientations were determined under both absolute (Type 1) and relative (Type 2) coordinate systems, morphological groups were identified based on differences in appearance. Taxonomic names were allocated to these morphological groups with consideration given to morphological variations, ontogenetic changes, and most importantly, whether the holotypes and relevant specimens could be included within these morphological groups. Our study yielded a total of 10 genera and 34 species/subspecies, including three new genera (Sphaeropylolena n. gen., Sphaerolarnacillium n. gen. and Qiuripylolena n. gen.) and 20 new species/subspecies in the superfamily Pylonioidea (Larcospira teres n. sp., L. tetragonicentrum n. sp., Larcopyle buetschlii chenmuhongi n. subsp., L. buetschlii orion n. subsp., L. molle n. sp., L. eccentricanoides n. sp., L. pulchella n. sp., Sphaeropylolena laxa n. sp., S. tenellispinosa n. sp., Phorticium itakii n. sp., P. scitulum n. sp., Sphaerolarnacillium cochleatum n. sp., S. exactum n. sp., S. tanzhiyuani n. sp., Qiuripylolena chikuchik n. sp., Q. pompon n. sp., Q.? multiconcentrica n. sp., Circodiscus biorbiculus n. sp., C. pseudomicroporus n. sp., and Tholomura pilula n. sp.). Following this taxonomic scheme, we confirmed the limited geographic distribution of many pylonioid species.