Helicosphaerella perch-nielseniae

Helicopontosphaera perch-nielseniae Haq, 1971

Helicosphaera perch-nielseniae (Haq, 1971) Jafar & Martini, 1975

Sub-rectangular helicolith having an asymmetrical blanket (Type II, Helicosphaerella recta type) blanket, a truncated flange termination and a central area with indistinct, conjunct inverse bar creating hardly visible, indistinct slit-like openings at both sides (only observable at 45° in polarised light). The initial section of the flange from the origin is inversely oriented and makes about the right angle with the final termination.

Helicosphaerella perch-nielseniae differs from Helicosphaera truncata (Bramlette & Wilcoxon, 1967) Aubry, Liu, de Vargas, & Probert in Aubry & Bord (2009) and Helicosphaerella recta (Haq, 1966) Aubry, Liu, de Vargas, & Probert in Aubry & Bord (2009) by having an inverse bar with indistinct slit-like pores at both sides of it whereas the latter species have traverse bars with a larger opening at both sides of it.

The initial section of the flange from the origin is inversely oriented in Helicosphaerella perch-nielseniae whereas transversely oriented in Helicosphaera truncata and Helicosphaerella recta.

Helicosphaerella perch-nielseniae is distinguished from Helicosphaerella obliqua (Bramlette & Wilcoxon, 1967 ) Aubry, Liu, de Vargas, & Probert in Aubry & Bord, 2009 by having indistinct slit-like openings whereas later has distinct larger openings at both sides of the conjunct inverse bar. Moreover, Helicosphaerella perch-nielseniae is sub-rectangular whilst Helicosphaerella obliqua ovoid in shape.

The initial section of the flange from the origin is inversely oriented in both species and makes about the right angle with final termination in Helicosphaerella perch-nielseniae whereas acute angle in Helicosphaerella obliqua.

Aubry, M. -P., Bord, D., 2009. Reshuffling the cards in the photic zone at the Eocene/Oligocene boundary. In: Koeberl, C., Montanari, A. (eds), The Late Eocene Earth-Hothouse, Icehouse, and Impacts. Geological Society of America, Special Papers 452, 279-301.

Bramlette, M. N., Wilcoxon, J. A., 1967. Middle Tertiary calcareous nannoplankton of the Cipero section, Trinidad, W.I. Tulane Studies in Geology and Paleontology 5, 93-131.

Haq, B. U., 1966. Electron microscope studies on some upper Eocene calcareous nannoplankton from Syria. Stockholm Contributions in Geology 15, 23-37.

Haq, B. U., 1971. Paleogene calcareous nannoflora. Parts I-IV. Stockholm Contributions in Geology 25, 1-158.

Jafar, S. A., Martini, E., 1975, On the validity of the calcareous nannoplankton genus Helicosphaera. Senckenbergiana Lethaea 56, 381-397.