Recent Arborescent Dendrophryid Foraminifera Found On Upper Pleistocene Cold-water Corals from the Inner Sea of the Maldives

Abstract

Abstract Recent specimens of Spiculidendron were found on Late Pleistocene (21,400–22,500 BP) cold-water corals from the sea floor at 457 m depth of the inter-atoll Kardiva Channel of the eastern row of the Maldives archipelago. Spiculidendron and other dendrophryid foraminifera (Rhizammina-like forms) exclusively colonized specimens of the genus Enallopsammia, which was characterized by a phosphatic-stain surface. The Spiculidendron wall was composed of sponge spicules, elongated diatom frustules, tests of juvenile benthic and planktic foraminifera, and calcareous nannoplankton, among other materials. Sponge spicules and elongated diatom frustules were arranged longitudinally, with foraminiferal tests and other bioclasts packed in between, indicating that the agglutination process of Spiculidendron is selective with respect to the manner of growth. In the most distal parts of the branches, only sponge spicules and elongated diatom frustules were present, working as guides for the test construction, prior to the agglutination of juvenile foraminiferal tests and other bioclasts. Moreover, in the sediment associated with the coral fragments, 94 species of benthic foraminifera were identified, an assemblage distinct from the taxa incorporated into the agglutinated Spiculidendron tests. The process of wall growth is complex and ordered. This foraminifer, as well as the Rhizammina-like specimens, tolerates dysoxic conditions (0.896 ml/l) and low temperature (12°C). This observation represents a new record of Spiculidendron from the Indian Ocean and from deeper (aphotic) environments than previously reported from the shallow waters of the Caribbean. A cryptobiontic habitat is interpreted for Spiculidendron.