Molecular study for symbiosis of the Polycystine radiolarians

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The phylogeny of the solitary polycystinean Radiolaria, which includes Dictyocoryne profunda Ehrenberg, D. truncatum (Ehrenberg), and Spongaster tetras Ehrenberg, with skeletons of opaline silica, was examined using 18S r DNA (small-subunit rDNA) gene sequence analysis.The 18S rDNA molecular phylogeny among Radiolaria suggested that the Polycystinea was divided into at least two distinct lineages consisting of the following taxa :(1)the colonial and skeletonless Polycystinea including the Collospaeridae, Sphaerozoidae, and Thalassicollidae ; and (2) the shell-bearing solitary Polycystinea including the Spongodiscidae. The "Polycystinea" thus clearly shows a paraphyly among Haeckel's Radiolaria. Moreover, the monophyly of the clade including the Acantharea and the solitary shell-bearing "Polycystinea" was supported by relatively high bootstrap values in the NJ, MP, and ML analyzes.This lineage is characterized by having mineralized radiate skeletons though there is a difference in the chemical components between SiO2 and SrSO4. Until now, although the Acantharea and the solitary shell-bearing "Polycystinea" have not been categorized into as one group, if a new taxonomic group among Radiolaria will be established based on the monophyly of the both clades, it may claim to find out other taxonomic criteria which could be latent in these organisms. The results thus suggested that the currently used taxonomic system in Radiolaria may need serious revision.