New species of the xenophyophore genus Aschemonella (Rhizaria: Foraminifera) from areas of the abyssal eastern Pacific licensed for polymetallic nodule exploration

Abstract

We describe Aschemonella monile Gooday and Holzmann sp. nov. from the Clarion-Clipperton Zone (CCZ, abyssal eastern equatorial Pacific), a region characterized by commercially significant concentrations of polymetallic nodules. The new species is the most abundant xenophyophore (giant agglutinated foraminifera) in our main sampling area (12-14°N; 116°30′-117°26′W). Additional specimens originate from the central CCZ, and from a third area, ∼900 km NW of the main area, where A. monile numerically dominates the megabenthos in photographic surveys of the seafloor (average densities 1.54 individuals/m 2; peak densities > 3 individuals/m 2). Aschemonella monile is much larger (≥ 7 cm in length) than previously described species of the genus, with a test comprising an irregular sequence of self-contained, partly overlapping 'segments', creating a multichambered structure. A similar, much rarer species from the main study area, described here as Aschemonella aspera Gooday and Holzmann sp. nov., has an unsegmented test with a very rough, coarsely agglutinated wall. Genetic data suggest that A. monile is distinct from A. aspera and most closely related to a group comprising Rhizammina algaeformis and Aschemonella ramuliformis. Both new species have delicate tests that are often attached to nodule surfaces, making them particularly vulnerable to seafloor disturbances.