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Multilocular specimen, side view Collected: Aug. 1995, N Kara Sea (St.Anna Trough), 530 mwd, modern mud |
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Unilocular specimen, apertural view Collected: 16 Oct. 1987, N Barents Sea, 230 mwd, modern mud |
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Two unilocular specimens encrusting a gravel; a - aperture, g - gravel, r - remnants of a third destroyed specimen Collected: 16 Oct. 1987, N Barents Sea, 230 mwd, modern mud |
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An agglomerate of two bilocular specimens; a - aperture of the larger specimen; f -- foramen of the large specimen where broken-off earlier chambers were attached; A.c. – cross-section of an embedded Alvelophragmium crassimargo test Collected: 16 Oct. 1987, N Barents Sea, 230 mwd, modern mud |
Remarks: | Distribution. On the Barents-Kara shelf this species is restricted
to oligotrophic deep-water areas (200-600mwd) where the surface sediment
consists of the so-called "brown mud" -- up to 40-cm-thick oxidized mud
enriched in manganese oxides. Sand and gravel fractions of this sediment
are mostly composed of R. pilulifer tests, predominantly dead.
Morphology. Test unilocular or multilocular. Chambers spherical;
constrictions between chambers deep - 1/2 test width. Aperture single,
roughly circular, on slightly projecting neck. Multilocular tests are up
to 5 chambers increasing in size; axis irregularly twisted; aperture points
any direction, typically at obtuse angle to test axis. Largest unilocular
tests and largest ultimate chambers of multilocular tests average 2 mm
in diameter, max 3.5 mm. Wall thickness 0.10-0.25mm, increases with chamber
size. Test wall robust, consists of poorly sorted mineral grains hold by
small amount of cement; dimensions of larger grains match wall thickness;
no selectivity for mineral types observed; often encrusts coarse debris
(gravel and small pebbles). Embedded foraminiferal tests are common and
picked selectively: only Alvelophragmium crassimargo, Cribrostomoides
subglobosus and conspecific specimens (Rose Bengal stained A.crassimargo
and C.subglobosus observed). In multilocular specimens the cytoplasm,
if present, occupies but the ultimate chamber; foramen sealed with a matrix.
Taxonomy. The species has been obviously misidentified in the Barents-Kara region for Hormosina globulifera. The morphology of the form from the Barents-Kara shelf matches well Brady's description of Reophax pilulifer, and this identification has been confirmed by C. Schoeder-Adams. However, the morphological variability of the species provides sound evidence that it is not a hormosinid -- rather a saccamminid:
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