''Miliamellus'' is a
genus of
Cenozoic
The Cenozoic ( ; ) is Earth's current geological era, representing the last 66million years of Earth's history. It is characterised by the dominance of mammals, birds and flowering plants, a cooling and drying climate, and the current configura ...
benthic foraminifera with tests made of imperforate
opaline silica. It is the only genus in the order Silicoloculinida and the family Silicoloculinidae. It is sometimes referred to by the junior synonym ''Silicoloculina''.
The family Silicoloculinidae, named by
Resig, ''et al.'', 1980, is characterized by tests that resemble those of the imperforate calcareous
Miliolidae
''Miliolidae'' is a family in the superfamily ''Miliolacea'' of miliolid foraminifera
Foraminifera (; Latin for "hole bearers"; informally called "forams") are single-celled organisms, members of a phylum or class of amoeboid protists charact ...
, or the finely agglutinated
Rzehakinidae
The Rzehakinidae is a family of Lower Cretaceous to recent formaminifera that resemble the calcareous imperforate Miliolidae
''Miliolidae'' is a family in the superfamily ''Miliolacea'' of miliolid foraminifera
Foraminifera (; Latin for "h ...
in which chambers are about half a coil in length and arranged in various planes. Resig et al. named the genus ''Silicoloculina'' for specimens recovered from below the
carbonate compensation depth
Carbonate compensation depth (CCD) is the depth in the oceans below which the rate of supply of calcite ( calcium carbonate) lags behind the rate of solvation, such that no calcite is preserved. Shells of animals therefore dissolve and carbonate ...
in the
Scotia Sea and the
Peru-Chile Trench. Loeblich and
Tappan synonymised this genus with ''Miliamellus'' in 1987.
''Miliammellus'', named by Saidova and Burmistrova, 1978, has a small ovoid test, up to 0.5 mm long with chambers arranged as in the miliolid ''
Quinqueloculina
''Quinqueloculina'' is a genus of foraminifera in the family Miliolidae.
As with all miliolids the test of ''Quinqueloculina'' is composed of imperforate, porcelaneous calcite, often giving them a yellowish tint. As with the Miliolidae, the ...
''. Chambers are slightly more than half a coil in length, resulting in successive whorls being offset, and are widest at their base, narrowing toward the aperture, a low arch at the end of the final chamber. ''Miliammellus'' has a range from the Upper Miocene to recent and has been found in the Bering Sea, Antarctic, north and central Pacific, and Indian Oceans at abyssal depths below 4,000 m. The type species is ''Miliammellus legis'' Saidova and Burmistrova, 1978.
Its test ultrastructure consists of small (5μm by 0.3μm), hollow rods of silica arranged in subparallel sheets, with an outer and inner organic membrane. The outer and inner organic layers are each approximately 0.1μm in thickness. The middle silica layer is about 19μm thick in total; it is further broken down into an outer, inner, and middle silica subunit. The outer and inner silica subunits are each approximately 0.2μm thick and consist of hollow silica rods arranged in subparallel sheets, with the elongation parallel to the surface. The middle silica subunit is approximately 18μm thick and consists of a randomly oriented lattice of hollow silica rods. No organic material is found within the open spaces between rods.
In overall shape as well as in ultrastructure, ''Miliamellus'' resembles
miliolilid foraminifera. However, the ultrastructure differs in that the rods of miliolid test walls are solid rather than hollow, smaller, and of course are made of
calcite
Calcite is a Carbonate minerals, carbonate mineral and the most stable Polymorphism (materials science), polymorph of calcium carbonate (CaCO3). It is a very common mineral, particularly as a component of limestone. Calcite defines hardness 3 on ...
.
References
* Systematics of modern foraminifera, from
Loeblich and
Tappan (1992), in Barun K. Sen Gupta 200
Modern Foraminifera* Forminiferal Genera and their Classification by Alfred R. Loeblich Jr and Helen Tappan, 1988
Miocene life
Silicoloculinida
Foraminifera genera
Silicoloculinidae
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