Catalog - Globigerina cristata

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Globigerina cristata

Citation: Globigerina cristata Heron-Allen & Earland, 1929

Type specimens: 1959.7.1.3 - Lectotype designated by Banner & Blow 1960

Type locality: The species, which appears to be very distinctive, is frequent in a dredging made by the " Discovery" on 24 July, 1927 , off Possession Island, S.W. Africa, in lat. 26" 17' 40" S., long. 14"36' 20"W. Depth, 3170 metres. The bottom was a very clean Globigerina ooze containing all the species normally found in an Atlantic ooze in such latitude, and many other forms of rarer occurrence, all in a remarkable state of preservation. A search through Challenger and other Atlantic material for this species-which, owing to the minute size of the crested forms, might easily have been overlooked-has not so far resulted in its discovery at other similar localities

Test minute, hyaline; a flattened trochoid spiral of from two to two and a half convolutions, with six or occasionally seven chambers, rapidly and regularly increasing in size, in each convolution. Dorsal surface almost flat, exhibiting all chambers. Ventral surface rounded and with the chambers of the last convolution only visible, the final chamber inflated and extending inwards over the umbilical cavity. Chambers inflated on the periphery and ventral side, flattened on the dorsal side. Sutures depressed and periphery deeply lobate in young specimens, markedly less lobate in the adult. Aperture an arch in the ventral umbilicus concealed by the extension of the final chamber.
In the early stages the walls are very thin and glassy, except on the peripheral edge, where each chamber is furnished with a solid knob or crest of shell substance covered with truncated spines. A few similar spines are distributed over the surface of the chambers near the peripheral edge. These solid extensions or crests form a very striking feature in the youngest,specimens, in which they frequently equal and often exceed in bulk the chamber on which they are formed. As the shell increases in size, the crests diminish, the shell substance being apparently resorbed and redistributed over the walls of the chambers, which become thickened all over. At this stage, which appears to mark the completion of growth, the peripheral edge is regularly lobulate, and the entire surface of the chambers is covered with short blunt spines. Further development is now limited to the shell wall, which continues to increase in thickness until finally we attain a form which is almost uniformly thick-shelled, having a rough but not spinous surface, and with peripheral lobulations and sutural depressions reduced to a minimum.

Description of lectotype.-The minute test consists of about two whorls of slowly enlarging chambers, arranged six to a whorl in a very low trochospire. The chambers are globular to subovoid with a tendency to slightly radially elongate. The chambers are equally inflated dorsally and ventrally and are but slightly embracing. The equatorial profile is subcircular, and the equatorial periphery is lobulate. The axial periphery is smoothly rounded and the test appears nearly parallel sided. The final chamber is bulla-like and extends from its normal position to cover the umbilicus, and it possesses simple tube-like prolongations extending along the intercameral sutures of the ventral side. The apertures of the final chamber open at the distal ends of the tube-like prolongations and are in line with the intercameral sutures of the final whorl. The intercameral sutures are distinctly and equally depressed both dorsally and ventrally; they are sinuous, slightly curved or nearly radial, and are not thickened or limbate. The wall is finely perforate. On all the chambers" except the last, the surface is finely hispid, but the hispidity becomes markedly stronger at the distal ends of the more elongate chambers. The final chamber is smooth. [Banner & Blow 1960]

Immature crested specimens range between 0.08 mm. and 0.11 mm. in greatest diameter, a considerableproportion of this size being due to the solid crests, which may be as much as 0.026 mm. in length compared with 0.022 mm., the breadth of the chamber to which the crest was attached. Fully-grown individuals range between 0.12 mm. and 0.18 mm. in diameter, and have a shell wall up to 0.026 mm. in thickness. Maximum diameter of lectotype: 0.145 mm. [Banner & Blow 1960]

From Banner & Blow (1960)

Taxonomic remarks: This species was first described from recent material dredged off Possession Island, S. W. Africa, (latitude 26 17' 40" S, longitude 14 26' 28" E) by the "Discovery" Expedition of 1925-1927. The lectotype of Globigerina cristata, here designated, came from a slide registered in the British Museum (Natural History) as ZF.3276; this slide was marked with full details of the locality mentioned above. The lectotype is deposited in the British Museum (Natural History), registered number 1959.7.1.3. It is possible that two minute but distinct species were included under this name by Heron-Allen and Earland, but it appears that neither has been recorded by any subsequent author. [Banner & Blow 1960]

Remarks: A great many specimens were present in the Heron-Allen and Earland collection and it was observed that the peculiar form of the last chamber described for the lectotype appeared to be a normal character for adult specimens of this species. In what appeared to be immature or damaged specimens the primary aperture of the last present chamber was seen to be a low, elongate, interiomarginal, umbilical-extraumbilical, slit-like opening. The peculiar final chamber seems remarkably constant in general shape and position and is similar to that described by Loeblich and Tappan (1957) for the distinct species Globigerinita parkerae. The species cristata may be referable to the genus Globigerinita Bronnimann 1951, as emended by Loeblich and Tappan 1957, but we discuss this further below (p. 37). This species has only been observed so far in collections from the recent seas. [Banner & Blow 1960]

References:

Banner, F. T. & Blow, W. H. (1960a). Some primary types of species belonging to the superfamily Globigerinaceae. Contributions from the Cushman Foundation for Foraminiferal Research. 11: 1-41. gs O

Heron-Allen, A. & Earland, A. (1929). Some new foraminifera from the South Atlantic II. Journal of the Royal Microscopical Society. 49(4): 324-334. gs

CATALOG OF ORIGINAL DESCRIPTIONS: Globigerina cristata Heron-Allen & Earland, 1929

Globigerina cristata

References:

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