Catalog - Globorotalia akersi

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Globorotalia akersi

Citation: Globorotalia akersi Snyder 1975

Type specimens: Holotype: USNM 216182; Paratypes: USNM 216181-5;

Type locality: Holotype: USNM 216182; maximum diameter, 0.87 mm; Kane Station 87. Paratypes: USNM 216181; maximum diameter, 0.60 mm; Alaminos Station 27E; USNM 216183; maximum diameter, 0.61 mm; Ala- minos Station 27E; USNM 216184; maximum diameter, 1.06 mm; Alaminos Station 24E; USNM 216185; maximum diameter, 0.79 mm; Alaminos Station 27E (not figured).

Type repository: Washington; USNM

The test is a large, moderately low trochospire with five to six and one-half gradually enlarging chambers in the final whorl. Coiling may be either dextral or sinistral, but the latter is dominant. The test is slightly to moderately biconvex, with the umbilical side in some specimens more strongly inflated. The outline in plan view is subquadrate, elliptical, or nearly round and the periphery is lobulate and carinate. Sutures are radial to slightly curved and depressed on the umbilical side, oblique to curved and nearly flush to limbate on the spiral side. The final chamber extends across the umbilicus to attach to earlier formed chambers of the final whorl. This chamber may continue in the same plane as earlier chambers of the final whorl or be markedly angled to that plane. It may be larger or smaller than the penultimate chamber but always extends across the umbilicus to obscure the primary aperture. The aperture lies along the basal margin of the modified final chamber and is either small and slit-like or appears as a series of small infralaminal openings.

Holotype: maximum diameter, 0.87 mm; Paratypes: 0.60-1.06 mm

Globorotalia akersi has close morphologic affinities with Globorotalia menardii and Globorotalia ungulata. Specimens with only slight biconvexity, a nearly round equatorial profile, and sutures that are limbate on the spiral side of the test (pl. 1 figs. 4-6; pl. 2, figs. 1-3) resemble Globorotalia menardii. This morphologic variant is numerically dominant. Specimens with more highly inflated chambers, an elliptical to subquadrate equatorial profile, and nearly flush to slighly limbate sutures on the spiral side of the test (pl. 1, figs. 1-3) resemble Globorotalia ungulata.

It is possible that the specimens included within Globorotalia akersi represent two lines of similar evolutionary development, one stemming from Globorotalia menardii and the other from Globorotalia ungulata. However, because of the scarcity of specimens (only 20 have been found) all variants have been assigned to a single species. About 20% of the specimens are highly contorted (pl. 2, figs. 4-5 ). Given the scarcity of specimens, any statement as to the significance of this would be purely speculative.

Globorotalia akersi can be distinguished from Globorotalia menardii and Globorotalia ungulata because its final chamber extends across the umbilicus and gives rise to a small, slit-like aperture or to multiple infralaminal apertures. Both Globorotalia menardii and Globorotalia ungulata lack the modified final chamber and have a large, high arched, umbilical-extraumbilical aperture.

Globorotalia akersi is encountered only in a small area of the south-central portion of the Gulf of Mexico. Within this restricted range it comprises less than 1% of the planktonic forarniniferal assemblage.

References:

Snyder, S. W. (1975). Snyder, S. W. (1975). A new Holocene species of Globorotalia. Tulane Studies in Geology and Paleontology. 11: 302-305. Tulane Studies in Geology and Paleontology. 11: 302-305. gs

CATALOG OF ORIGINAL DESCRIPTIONS: Globorotalia akersi Snyder 1975

Globorotalia akersi

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