Catalog - Globigerinita iota

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Globigerinita iota

Citation: Globigerinita iota Parker 1962

Type locality: Downwind station BG 73 (0-2 cm.), 43°48' S., 108°09' W. at a depth of 3080 M.

Type repository: Washington; USNM

Test small, trochospiral, low-spired, with a rounded, lobulated periphery, 2½-3 whorls visible on the spiral side, umbilical area typically covered by a restricted bulla having infraliminal apertures at the sutures of the previous chambers of the final whorl, sometimes slightly visible on the spiral side and variable in size and extent of the lobes; chambers subglobular, up to 13 in all, 5 in the initial whorl, 4-5 in the final one; sutures radial, depressed; wall thin, very finely perforate, smooth or very fine ly hispid; primary aperture umbilical-extraumbilical but not extending to the periphery, usually with a narrow lip; secondary infraliminal apertures of umbilical bulla small, arched, with narrow lips.

Greatest diameter of holotype: 0.22 mm., thickness 0. 12 mm. Specimens at the type locality have proloculus diameters of 9- 19µm., with an average of 14 µm (13 specimens). Typical specimens from Capricorn sta. HG 37, 13°05' S., 124°16.8' W., have proloculus diameters or 8- 20µm, with an average of 12 µm (21 specimens). If the variant discussed below is included, the results are the same (42 specimens).

Comparison: G. iota differs from G. humilis in its smoother wall, fewer chambers in a whorl, less compressed test, and in the fact that, rather than having a modified normal chamber form the lobed structure over the umbilical area, the umbilicus is covered by a reduced bulla which is not part of the "regular"" progression of chambers (see fig. 26a, c). It differs from G. glutinata in being more compressed, smaller, in the absence of the variable types of bullae typical of that species, in having fewer chambers and a somewhat larger proloculus.

Discussion: Presently included within the range of variation of this species is a form which seldom has an umbilical bulla, has more elongated chambers which increase more rapidly in size, and a more translucent wall (pl. 10, fig. 30). This form is very difficult to isolate from typical specimens lacking the umbilical bulla. It may be the form figured by Rhumbler as Globigerina radians. In the eastern Gulf of Mexico both forms occurred together to form the Globigerina sp. of Parker listed in the synonymy, which is not referable to "Globigerinita parkerae" as stated by Loeblich and Tappan (1957a) (see Globigerinita humilis). In eastern Mediterranean deep-sea cores, this variant sometimes reaches a very large size and is the more common form of the species. Proloculus measurements of this form from the Pacific are 9-15 µm., with an average of 12 µm. (21 specimens, 13°05' S., 124°16.8' W.). These specimens have a maximum of 15 chambers, with 5 in the initial whorl. These measurements are smiilar to those of the typical specimens at the same station (see above).

G. iota has not been reported from the plankton, unless Rhumbler's specimens are referable to it. The southern limit of its distribution in the South Pacific is not yet established. It is an ubiquitous species occurring in most samples except those from the Antarctic. Few samples have been studied between Lat. 50-60° S., but the species is common at 50° S."

References:

Parker, F. L. (1962). Parker, F. L. (1962). Planktonic foraminiferal species in Pacific sediments. Micropaleontology. 8(2): 219-254. Micropaleontology. 8(2): 219-254. gs

CATALOG OF ORIGINAL DESCRIPTIONS: Globigerinita iota Parker 1962

Globigerinita iota

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