ALBERT

Description: Foraminiferal evidence from the eastern equatorial Pacific and from the North Atlantic indicates that the dissolution of deep-sea carbonates was intensified during interglacials rather than during glacials, in contrast to widespread opinion. Pleistoccne dissolution cycles introduce a systematic bias into the Interpretation of calcareous fossil assemblages near and below the lysocline zone.

Description: Three closely related species ( A. beccarii (Linn.), A. batava (Hofker) and A. tepida (Cushman) have been studied. Each possesses a multilaminate “chitinoid” endoskeleton, the outermost lamina possessing imperforate pustulae of shape characteristic for the species. The pustulae are fused to segmented tubules of organically-bound carbonate granules; these tubules line the canaliculi linking the inner and outer perforations of the test wall, and differ only in length between the three species. The calcareous wall is essentially granular in internal morphology, and is built upon an organic framework in which the tubules play a significant part. The apertural structures are described, and it is confirmed that the toothplate is structurally continuous with the septal (“rotalid”) flap and the basal calcareous lamella of the test. The distribution of intrathalamous and extrathalamous cytoplasm in A. tepida is described, and the first sequential photographs of cytoplasmic extrusion are presented for Ammonia. The relationship between the organic skeleton, the calcareous exo- and endo-skeletons, and the cell, is discussed.

Description: Morphological characters, interrelations, evolutionary trends, synonymies, Stratigraphie and paleogeographic distribution of 15 species here included in Globigerinatheka are discussed and illustrated by line drawings and SEM mircographs. In order to stress their interrelations, all taxa—with the exception of G. semiinvoluta—are given subspecific rank in a trinomial System. Holotypes and some additional types of the taxa discussed, which originally were published at widely varying magnifications, are reproduced at a uniform scale to facilitate their comparison. By this procedure alone the four species subconglobata, indes, mexicana and semiinvoluta become clearly distinct. The final chamber/bulla problem, of some importance in the genus, is discussed and illustrated. Evidence is given that G. semiinvoluta is a valid species, and not a synonym of G. mexicana mexicana. Its variability is demonstrated by a series of SEM micrographs. One subspecies, G. subconglobata luterbacheri, is described as new.

Description: Planktonic foraminifera were collected from an oceanic front off Baja California, Mexico, during April and May, 1965, in connection with studies of the physical oceanography of the front. Four major water masses were present: Southern Surface Water at approximately 0-50 m, Northern Surface Water, forming a submerged intermediate layer between about 150-50 m, Southern Deep Water below 150 m, and Northern Deep Water deeper than 250 m. Planktonic organisms smaller than 2 mm were concentrated in the surface waters, suggesting that food for foraminifera was most abundant there. Organisms larger than 2 mm, considered a measure of potential predators of foraminifera, were abundant in both surface and intermediate waters. Most foraminiferal concentrations were from 1 to 100 specimens per m :J, with the largest concentrations in Southern Surface Water above the front and in deep water along the front. Lowest concentrations were in intermediate water, except in the frontal mixing zone, and at depths below 450 m. Empty shell concentrations were about one-tenth of associated living concentrations. Possible errors of concentration estimates were assessed by comparing paired net and paired tow results. Seventy percent of these estimates appear to be precise within a factor of 1.3. The error introduced by patchiness probably is much larger. Four foraminiferal assemblages are recognized: ( 1 ) Southern Surface Water assemblage, (2) widespread species with southern affinity which apparently tolerate the intermediate water, ( 3) species brought in with the submerged northern water, and ( 4) the assemblage inhabiting the deep waters. The estimated average minimum flux of empty shells was approximately 6% of the living standing crop I day by volume. The relative empty shell output was greater than this for many intermediate water species, and less for species restricted to southern and to deep water. The intermediate layer contributed approximately one-half of the empty shell flux, where specimens with small terminal chambers (kummerforms) were abundant. The sediment produced in the front contained about 50% kummerforms, but the total standing crop of living foraminifera contained only about 10%. The tongue of advected intermediate water may have represented an unfavorable habitat for foraminifera, where northern species were submerged and possibly deprived of food or otherwise impeded in their normal growth. Southern species also may have been displaced from their normal habitat by mixing processes. These displacements are suggested as one cause for the formation of small terminal chambers in specimens inhabiting intermediate depths. Empty shells apparently arise through reproduction, stress from displacement, and predation, with predation being the least important mechanism.

Description: The foraminifer Rosulina globularis d'Orbigny from natural and laboratory populations is occasionally preyed upon by free-living, marine nematodes. Borings 3.7 to 14.3 in diameter in the tests of living and dead specimens of R. globularis and dead specimens of Eolivina doniezi Cushman and Wickenden from the same natural and laboratory populations are attributed to the predaceous nematodes. Predation in the laboratory populations is greater than in the natural populations, especially among juvenile specimens of R. globuluris. Borings in R. globuluris occur characteristically in the outer whorl, whereas, those in B. doniezi are generally confined to the apertural half of the test. This preference for the area of wall penetration is thought to correspond to the accessibility or living position of the prey. However, several incomplete borings coincide with test pores, and thus represent test penetration in an area of least resistance. Identical borings occur in Holocene and Cretaceous bathyal and neritic foraminifers. Another kind of borings in these specimens, while in part resembling gastropod boreholes, may likewise be due to soft-bodied organisms. Evidence of predation provides ecologic and paleoecologic information on the living habits, habitat, and community structure of the foraminiferal prey, and can directly influence the interpretation of foraminiferal production and rates of sedimentation based on foraminiferal production.