Catalog - Laeviheterohelix

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Laeviheterohelix

Citation: Laeviheterohelix Nederbragt, 1991

Type species: Guembelina pulchra Brotzen 1936

Diagnosis: Test calcareous, biserial throughout or with an initial planispiral coil; wall microperforate and smooth with scattered pustules, or with pores situated in the center of a pore mound. Aperture a simple arc, bordered by distinct flanges.

the Latin word "laevis" means smooth

Remarks: The genus Laeviheterohelix is here proposed for the smooth heterohelicids (L. pulchra. L. glabrans, L. dentata, and two new species, L. turgida and L. flabelliformis). The wall structure of these forms differs from that of other heterohelicids, in being non-costate and microperforate; the average pore-size is around 0.8µm. All other heterohelicid species are costate and have larger pores. Heterohelix moremani is the single other species that may have a smooth test; but such smooth forms occur together with costate specimens.

Two types of wall structure are found in Laeviheterohelix specimens. The wall is either smooth with scattered pustules in between which the pores are situated or the wall is covered with small mounds in the center of which the pores are found. The same two types of wall structure occur in two other planktic foraminiferal genera, in Cassigerinella Pokomy (Saito and Biscaye 1977) and in Guembelitria Cushman (Kroon and Nederbragt 1990). The wall structure of Laeviheteroltelix differs qualitatively from that of the other costate heterohelicids. Alignment of pustules on microperforate specimens from less well preserved scdiments can give the appearance of costae, but such structures appear to be diagenetic rather than primary. Laeviheterohelix pulchra is the only species known to have a smooth morphotype as well as one covered with pore mounds. Apart from wall structure the two types are morphologically identical. However, all specimens in a single population from one location have the same wall structure. The difference may be ecophenotypic.

Range: Turonian to end of the Maastrichtian.

References:

Kroon, D. & Nederbragt, A. J. (1990). Ecology and paleoecology of triserial planktic foraminifera. Marine Micropaleontology. 16: 25-38. gs

Nederbragt, A. J. (1991). Late Cretaceous biostratigraphy and development of Heterohelicidae (planktic foraminifera). Micropaleontology. 37: 329-372. gs

Saito, T. & Biscaye, P. E. (1977). Emendation of Riveroinella martinezpicoi Bermúdez and Seiglie, 1967, and synonymy of Riveroinella with Cassigerinella Pokorný, 1955. Micropaleontology. 23: 319-329. gs

CATALOG OF ORIGINAL DESCRIPTIONS: Laeviheterohelix Nederbragt, 1991

Laeviheterohelix

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			Laeviheterohelix flabelliformis Nederbragt 1991 = Laeviheterohelix flabelliformis
			Laeviheterohelix turgida Nederbragt 1991 = Laeviheterohelix turgida