Catalog - Clavatorella nicobarensis

This page provides data from the catalog of type descriptions. The catalog is sorted alphabetically. Use the current identification link to go back to the main database.

Other pages this level: C. nicobarensis, C. paleocenica, C. salumensis

Clavatorella nicobarensis

Citation: Clavatorella nicobarensis Srinivasan & Kennett 1974

Type age (chronostrat): The type sample (S87C/Mfl9) is very rich in planktonic foraminifera and has yielded 36 species including the new species. The diagnostic assemblage of Pulleniatina primalis, "Globoquadrina"" humerosa, Sphaeroidinellopsis subdehiscens paenedehiscens, Sphaeroidinella dehiscens (forma immatura), Globorotalia menardii and G. multicamerata accompanied by Globorotalia margaritae indicates that the type sample is from within the G. margaritae Zone of Bolli (1970). Globorotalia margaritae has been recognized in Central and South America, Mediterranean, and Indo-West Pacific (Bolli, 1970; Lamb and Beard, 1972; Cita, 1973; Kennett, 1973) and seems a reliable index species for the Early to early Middle Pliocene."

Type locality: Kakana section (S87C/Mfl9), Car Nicobar Island, Bay of Bengal.

Type repository: Washington; USNM

Test free, small, outline deeply lobate, coiled in low trochospire; dorsal side evolute, ventral side involute with moderately shallow umbilicus. The spire is mostly level with or depressed below dorsal surface of final whorl of chambers (pl. 1, figs. 1, 11) giving false impression of biumbilicate, planispiral test. Large specimens consist of nearly two whorls containing nine or more chambers with five (or rarely six) in final whorl. Early chambers spherical to subspherical with later chambers progressively more radially elongate; sutures on dorsal and ventral sides essentially radial, slightly curved, and depressed. Wall penetrated by closely spaced pores and surface roughened by cancellate ridges between pores and by irregular calcite growths on ridges. Aperture simple, extending from the umbilicus to the periphery along base of final chamber, showing individual variation in height, and bordered by distinct, uniform, perforate lip, throughout length. Aperture does not extend across the periphery onto dorsal side. Ninety percent of the tests are dextral

Protentella prolixa Lipps. SRINIVASAN and SHARMA 1973, pl.3 fig. 6 (non Protentella prolixa Lipps, 1964)

Remarks: Clavatorella bermudezi (Bolli) is most closely related to C. nicobarensis but differs in swollen extremities of later chambers which are much more separated at their attenuated proximal ends; also the wall surface is distinctly pitted. The former species also has similar depressed trochoid coiling and shallow umbilical depression and a comparably placed but more elevated aperture. It appears to be the direct ancestor of C. nicobarensis. According to Blow (1969) C. bermudezi ranges from the upper part of Zone N8 (late Early Miocene) to the lower part of Zone NI0 (early Middle Miocene).
Protentella prolixa (Lipps) differs in being planispiral and in having an equatorial symmetrical aperture. Juveniles of Clavatorella nicobarensis resemble Turborotalia in gross morphology. The surface texture, however, differs from that of Turborotalia, and the radially elongate chambers of the adult are characteristic of Clavatorella and related genera.

General discussion: Blow (1965) recognized that forms having radially elongate chambers may be divided into three groups each having a characteristic coiling mode and apertural position. Blow considered Bolliella to include those species of Hastigerininae with radially elongate chambers and Beella to include species of Globigerininae with radially elongate chambers. He proposed Clavatorella for the third group which includes species of Globorotaliinae with radially elongate chambers. Blow considered Hastigerinella to be a special case representing a combination of streptospiral coiling and radially elongate chambers. According to Blow (1965) these groups arose by parallel evolution in different stocks and are phylogenetically unrelated.
Scanning electron microphotographs show that Clavatorella nicobarensis n. sp. and Recent Beella digitata (Brady) have similar surface features. Both have a fine irregularly cancellate pattern of raised ridges surrounding pores and irregularly distributed tubercles on the ridges. Juvenile specimens of B. digitata have been observed with an umbilical-extra umbilical aperture similar in position to that of C. nicobarensis. Some juvenile specimens of Beella digitata also closely resemble juvenile specimens of C. nicobarensis (pI. 1, fig. 8). In adult forms of C. nicobarensis the aperture remains extra umbilical whereas it is umbilical in adult B. digitata. Therefore, we conclude that B. digitata is closely related to C. nicobarensis and that the significance of the difference in apertural position in adults is insufficiently understood now to be used as a basis for separation at the generic level.

References:

Lipps, J. H. (1964). Miocene planktonic foraminifera from Newport Bay, California. Tulane Studies in Geology and Paleontology. 2: 109-133. gs O

Srinivasan, M. S. & Kennett, J. P. (1974a). A planktonic foraminifer (Clavatorella) from the Pliocene. Journal of Foraminiferal Research. 4(2): 77-79. gs

Srinivasan, M. S. & Sharma, V. (1973). Stratigraphy and microfauna of Car Nicobar Island, Bay of Bengal. Journal of the Geological Society of India. 19: 1-11. gs

CATALOG OF ORIGINAL DESCRIPTIONS: Clavatorella nicobarensis Srinivasan & Kennett 1974

Clavatorella nicobarensis

References:

Add Comment

Comments