Xenophyophores (Protista, Foraminifera) from the Clarion-Clipperton Fracture Zone with description of three new species

Abstract

We describe three new and one poorly-known species of psamminid xenophyophores (giant foraminifera), all of which were found attached to polymetallic nodules in the Russian claim area of the Clarion-Clipperton Fracture Zone (CCFZ; abyssal eastern equatorial Pacific, 4,716–4,936 m water depth). Semipsammina licheniformis sp. nov. is the second species of the genus to be formally described. The test encrusts the surface of the host nodule forming a flat structure with a rounded outline and rather irregular concentric zonation. The wall comprises a single layer, composed mainly of radiolarian skeletons, covering granellare branches and stercomata strings that lie directly adjacent to the nodule surface. Psammina multiloculata sp. nov. has an approximately semi-circular, upright test with a weak concentric zonation that is attached to the nodule by a short stalk. The outer test layer comprises radiolarian fragments, sponge spicules, and mineral grains; the interior is divided into small compartments containing the stercomare and granellare. Psammina limbata sp. nov. has a plate-like, sometimes curved, semi-circular test attached to the nodule surface by basal root-like structures. The composition of the test is similar to that of P. multiloculata, but the interior is not compartmentalised. The most distinctive feature is the lighter colour of the curved outer margin compared to other parts of test. With the addition of these and other species described during recent decades, Psammina has become a rather unwieldy taxon that requires revision. Spiculammina delicata Kamenskaya 2005, previously known from a single specimen, is the most abundant species in our collection. The test exhibits considerable morphological variation, particularly in terms of the degree of branching. The new specimens confirm the placement of this species in the family Psamminidae rather than the Syringamminidae, which it superficially resembles, as well as its sessile mode of life. Two additional species in our material, Stannophyllum radiolarium Haeckel, 1889 and Stannophyllum sp., belong to the order Stannomida. Like the psamminid species, both were found attached to nodules. Xenophyophores are a dominant megafaunal taxon within the CCFZ. Although limited, our new material suggests that this region hosts many novel taxa.