PALEOECOLOGY AND ECOLOGY OF XENOPHYOPHORES

Xenophyophores are large (several mm to 25 cm diameter), agglutinating protozoans, found primarily in the deep sea. Tests range from simple fans, discs or mudballs, to elaborately folded or reticulated forms, and often contain specific particle types or sizes. Xenophyophore densities are highest on sloped sediments associated with seamounts, continental slopes, canyons and trenches, and beneath productive surface waters. Most forms live as epibenthos on hard or soft substrates, feeding on surface deposits and suspended particles, but one endobenthic genus has been described. Modern xenophyophores enhance particle flux to the seabed, creating local regions of intense radiotracer and metazoan activity. Features key to xenophyophore identification in the fossil record include distinct test morphologies that sometimes involve incorporation of globigerinacean tests, sandwich-like structure in cross section, concentrations of barite (found within the protoplasm), and the presence of fecal strands containing many 10 to 20 mm fecal pellets having enhanced Pb contents. While xenophyophores have no confirmed fossil record, modern structures resembling the ichnogenus Paleodictyon are made by endobenthic xenophyophores in the genus Occultammina. Parallel distributions, morphologies and behaviors have been proposed for some graphoglyptid trace fossils, and for some xenophyophores in the families Syringamminidae and Reticulamminidae. Both occur in the deep sea, have regular or irregular network morphologies, and have been proposed to garden bacteria, trap meiofauna, or suspension feed. Fossils previously regarded as phylloid and fucoid algae, and several species of Aschemonella, previously regarded as foraminiferids, have lifestyles and morphologies consistent with those of modern epibenthic xenophyophores. Confirmation of xenophyophore presence in stratigraphic sequences could provide paleohabitat information and help elucidate the origins of this protozoan group.