Phaeodaria: Diverse Marine Cercozoans of World-Wide Distribution

Abstract

Phaeodarians are unicellular marine protists characterized by the "central capsule" containing the nucleus, the "phaeodium", or mass of brown particles, and a siliceous skeleton called the "scleracoma". Phaeodaria have long been classifi ed as a member of the Radiolaria; however, this protist group now belongs to the phylum Cercozoa. The ancestor of phaeodarians is thought to have appeared in the upper Triassic Epoch according to the fossil record. They reproduce by cell division and swarmer production. These plankton are heterotrophic, and they presumably feed on organic materials suspended in the water column or capture other plankton. Although this group is widely distributed in the world ocean from the surface to deep waters, they have attracted little attention from marine researchers partly because their abundance has long been underestimated. Recent study, however, revealed that phaeodarians are more numerous than expected, and their high abundance is sometimes reported. Considering their occasional high biomass and the fact that their scleracoma is made chiefl y from silica, this plankton group plays an important role in local ecosystems and has a large impact in the silica cycle of the ocean. Knowledge of phaeodarian is indispensable for future oceanography; therefore the hitherto-known information on this marine protist is comprehensively reviewed in this chapter.

Optics-based surveys of large unicellular zooplankton: a case study on radiolarians and phaeodarians

“…Although the precise vertical distributions of radiolarians and phaeodarians have not been well-clarified, the present results reflect the prevailing assumption that radiolarians with algal symbionts occur mainly in the layers shallower than the zones where phaeodarians live (Takahashi & Anderson 2002, Nakamura & Suzuki 2015a. Future studies should collect more optics-based data and further clarify the vertical distribution patterns of these unicellular zooplankton.…”

“…The skeleton of this family possesses several long branch-like extensions called styles (Nakamura & Suzuki 2015a), by which 2-3 individuals are occasionally connected together forming a colony (Fig. 2R, Swanberg et al 1986, Extended Data Figure 2c in Biard et al 2016).…”

“…Large phaeodarians have been reported to comprise up to 22.3% of the total zooplankton biovolume in the Sea of Japan (Nakamura et al 2013), and 2.7-13.7% in the western North Pacific (Steinberg et al 2008). It is, therefore, suggested that these unicellular zooplankton can play an important role in the silica cycle and the ecosystem in the oceans (Riemann 1989, Lampitt et al 2009, Nakamura & Suzuki 2015a. Phaeodarians and collodarians are the most important contributors to the biomass of Rhizaria, which has been estimated to comprise 33% of the total zooplankton abundance worldwide (Biard et al 2016).…”

An exploratory study of heterotrophic protists of the mesopelagic Mediterranean Sea

“…For the phaeogromida phaeodarian radiolarians (i.e. Challengerids, Medusettids, Lirellids) the works consulted were Kling and Boltovskoy (1999), Nakamura and Suzuki (2015), and Borgert (1906Borgert ( , 1911. For the Amphisolenid dinoflagellates (species of Amphisolenia and Triplosolenia) works consulted were Kofoid (1906), Kofoid and Skogsberg (1928), and Taylor (1976).…”

“…Pheodarian radiolarians of the order Phaeogromidae (e.g. Challengarids) are generally considered to be deep-water residents (Anderson, 1983;Kling and Boltovskoy, 1999;Nakamura and Suzuki, 2015) largely feeding on sinking organic aggregates (Gowing and Bentham, 1994;Nothing and Gowing, 1991). Heterotrophic dinoflagellates of the family Amphisoleniaceae group species of the enigmatic genera Amphisolenia and Triplosolenia, species of which lack chloroplasts but host endosymbionts.…”