Occultammina
Occultammina is a genus of xenophyophorean foraminifera known from the Atlantic and Pacific oceans. It is notable for being the first known infaunal xenophyophore as well as for being a possible identity for the enigmatic trace fossil Paleodictyon.
Like all other known xenophyophores, Occultammina is found in the deep ocean; the first known specimen was first discovered in 1980 at a depth of 8,260 m (27,100 ft) in the Ogasawara Trench, off the coast of Japan and described in 1982 by a joint research team from the University of Copenhagen and the University of Tokyo.[1] Further specimens referred to Occultammina sp. have been found at a depth of 4,844 m (15,892 ft) in the Porcupine Abyssal Plain, in the North Atlantic.[2] Further studies have expanded its geographical and bathymetric range from 3,000 and 8,260 metres (9,840 and 27,100 ft) in the Ogasawara Trench and from 4,500 to 4,800 metres (14,800 to 15,700 ft) in the North Atlantic, and also recorded its presence at 6,440 m (21,130 ft) in the Japan trench.[2] Occultammina sp. has also been recovered at a depth of about 4,050 metres (13,290 ft) near the Clipperton Fracture Zone, off the coast of western Mexico.[3]
Occultammina is infaunal; it typically is found at a depth of 6 cm (2.4 in) or less below the sediment's surface.[2] It was the first known infaunal xenophyophore.[4]
Occultammina is an exceptionally large single-celled organism; like other xenophyophores it constructs a complex, single-chambered shell or "test" from sediment particles. It grows in a net-like shape, the test consisting of hollow tubes that branch or form loose polygons. It is typically flattened compared to other xenophyophores.[1] It also has vertically ascending tubular outlets.[2] Occultammina tubes are similar to those of Tendalia in general shape, though the test structure differs.[5]
The test wall typically ranges from 70-120μm in thickness; it is poorly cemented and consists of two layers. The outermost is 15-30μm in thickness and composed primarily from clay; the inner layer is 50-90μm thick and composed of silt and radiolarian tests. The interior of the test lining has between one and four ridges separating the stercomares, or waste masses.
Individual Occultammina tubes are between 0.38 and 1 cm (0.15 and 0.39 in) in diameter.[1][4] Networks of Occultammina sized 5–10 cm (2.0–3.9 in) across have been found at the Ogasawara trench.[2]
