A xenophyophore found just below the surface of a box core of modern deep-sea sediment from the Japan Trench has a threadlike plasma body that extends through horizontal, anastomosing networks of organically bound sediment tubes (the organism's test). The tubes resemble somne of the polygonal networks of the trace fossil Paleodictyon. Such xenophyophores may be the makers of Paleodictyon, and the complex, regular geometry of Paleodictyon may be determined by the xenophyophore's anastomosing body shape.