Topics on the spatial distributions, standing stocks, and symbiosis of living Radiolaria (Rhizaria, Protoctista)

Noritoshi Suzuki, Yoshiaki Aita

Research output: Contribution to journalArticlepeer-review

5 Citations (Scopus)


Living Radiolaria consists of five orders, Acantharia, Collodaria, Nassellaria, Spumellaria and Taxopodia, based on molecular phylogenetic analyses. Most of the Radiolaria show a similar mode of life in the ocean. However, some exhibit a rather different mode of life: such taxa as Collodaria, Nassellaria and Spumellaria are generally pelagic planktonic protoctistians, whereas Acantharia and Taxopodia are found not only in open oceans but also in enclosed waters like the Seto Inland Sea. There are no radiolarians living in brackish water, except for a nassellarian Lophophaena rioplatensis, and neither have benthic radiolarians been recorded. A few species belonging to Nassellaria and Spumellaria live in the intermediate or deeper waters. The abundance of radiolarians is also different among radiolarian Orders. Collodaria are concentrated in very shallow surface waters, Acantharia are dominant above 20-m water depths. Nassellaria and Spumellaria show abundance peaks above and below the chlorophyll maxima zone, and Taxopodia tends to be abundant around the thermocline. Most of the radiolarians in the middle to tow latitudes (except for Taxopodia) harbor algal symbionts that supply a substantial amount of nutrition to their hosts. In particular, almost all the acantharian vegetative cells and collodarian cells are associated with algal symbionts so that they are one of the dominant planktonic forms in nutrient-depleted areas. Although radiolarians are likely to be a minor component of marine protists, they are useful for understanding the oceans of the past and planktonic ecosystems because their fossil records go back to more than 500 million years ago (early Cambrian Period).

Original languageEnglish
Pages (from-to)40-48
Number of pages9
JournalBulletin of the Plankton Society of Japan
Issue number1
Publication statusPublished - 2011 Feb


  • Cytology
  • Diversity
  • Molecular phylogeny
  • Radiolaria
  • Symbiosis


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