Selective zircon accumulation in a new benthic foraminifer, Psammophaga zirconia, sp. nov.

Abstract

Benthic foraminifera are single-celled eukaryotes that make a protective organic, agglutinated or calcareous test. Some agglutinated, single-chambered taxa, including Psammophaga Arnold, 1982, retain mineral particles in their cytoplasm, but the selective mechanism of accumulation is not clear. Here, we report the ability of a foraminiferal species to select and accumulate zircons and other heavy minerals in their cytoplasm. In particular, the use of Scanning Electron Microscope coupled with an Energy Dispersive X-ray microanalysis system (SEM-EDS) enabled a representative overview of the mineral diversity and showed that the analysed Psammophaga zirconia sp. nov. individuals contained dominantly crystals of zircon (51%), titanium oxides (27%), and ilmenite (11%) along with minor magnetite and other minerals. The studied specimens occur in the shallow central Adriatic Sea where the sediment has a content of zircon below 1% and of other heavy minerals below 4%. For that reason we hypothesize that: (i) P. zirconia may be able to chemically select minerals, specifically zircon and rutile; (ii) the chemical mechanism allowing the selection is based on electrostatic interaction, and it could work also for agglutinated foraminifera (whether for ingestion, like Xenophyophores, or incorporation in the test as in many other described taxa). In particular, this aptitude for high preferential uptake and differential ingestion or retention of zircon is reported here for the first time, together with the selection of other heavy minerals already described in members of the genus Psammophaga. They are generally counted among early foraminifera, constructing a morphologically simple test with a single chamber. Our molecular phylogenetic study confirms that P. zirconia is a new species, genetically distinctive from other Psammophaga, and occurs in the Adriatic as well as in the Black Sea.

Biologically agglutinated eukaryotic microfossil from Cryogenian cap carbonates

“…The mineral composition and sizes of grains in microfossils from the Taishir, Kakontwe and Rasthof formations, while offering little evidence to support formation of authigenic minerals around siliceous or organic‐rich walls, are consistent with those of modern agglutinating testate organisms. Modern examples of agglutinating microbes actively collect and select for specific types of mineral grains from the sediment and cement them together with silica, calcite or organic cements (Armynot du Châtelet, Guillot, Recourt, Ventalon, & Tribovillard, ; Nikolaev et al., ; Sabbatini et al., ; Šatkauskienė, ; Vohník et al., ). These organomineral associations have a high preservation potential because they retain both detrital grains and the organic component, and acquire a stronger signal of diagenetic quartz over time (McNeil et al., ).…”

“…Some of these are flat, micaceous grains with uniform sizes within a given organism (Armynot du Châtelet et al., ; Šatkauskienė, ). In fact, some modern lobose amoebae and foraminifera select for minerals that comprise only a small fraction of the bulk sediment, and may concentrate minerals such as zircons, ilmenite and titanium (Armynot du Châtelet et al., , ; Makled & Langer, ; Sabbatini et al., ). The large concentrations of minerals in tests relative to the surrounding micrite or the microbial laminae (cf.…”

“…The most distinguishing features of tests described here include blunt or curved edges or tear shapes. Indeed, round, spherical, ovoid and tear‐shaped morphologies are present in some modern lobose testate amoebae, including species of the group Arcellinida (Amoebozoa) such as Heleoperidae, Plagiopyxidae and Difflugidae (Bosak, Lahr et al., ; Bosak, Macdonald et al., ; Gomaa, Todorov, Heger, Mitchell, & Lara, ; Gomaa et al., ; Lahr & Lopes, , 2009; Vohník et al., ) as well as in some modern agglutinating foraminifera, such as saccamminids and psammosphaerids (Gooday et al., , ; Ohkawara et al., ; Rodrigues et al., ; Sabbatini et al., ). A new morphology is also present in these microfossil assemblages: round structures with concave edges, which suggest intentional formation by an organism.…”

Micro-CT 3D imaging reveals the internal structure of three abyssal xenophyophore species (Protista, Foraminifera) from the eastern equatorial Pacific Ocean

“…Some small monothalamids, notably flask-shaped saccamminids in the genus Psammophaga , also collect heavy minerals (magnetite, titaniferous magnetite, ilmenite, rutile, zircon, among others) within their cytoplasm 27 – 29 . Since the crystals are generally concentrated inside the aperture, it is possible that they serve to ballast this end of the test so that the aperture is directed towards the sediment 30 .…”

Soft-shelled foraminifera of the Black Sea and the Sea of Azov

“…В последнее десятилетие появилась информация о селективной способности мягкораковинных фораминифер рода Psammophaga Arnold, 1982 аккумулировать в цитоплазме клетки кристаллы определенных минералов (магнетита, титаномагнетита и циркона). В мелководных донных отложениях западной Антарктики обнаружены два вида рода Psammophaga, несущих в своей цитоплазме кристаллы магнетита и титаномагнетита (Pawlowski et al, 2011), а в Адриатическом море -один вид с включением в цитоплазме кристаллов циркона (51%) и окиси титана (27%) (Sabbatini et al, 2016). Подобные находки послужили основанием для названий новых видов, описанных указанными авторами: Psammophaga magnetica Pawlowski et Majewski, 2011и P. zirconia Sabbatini et al, 2016, и уточнена видовая принадлежность Allogromia crystallifera Dahlgren, 1962как P. crystallifera (Dahlgren, 1962.…”