Sphaeroidinellopsis paenedehiscens Blow 1969 from: Chaisson, W.P.Pearson, P.N. (1997): Planktonic foraminifer biostratigraphy at Site 925: middle Miocene–Pleistocene. In: Proceedings of the Ocean Drilling Program, Scientific Results Vol. 154 Eds: Shackleton, N.J.Curry, W.B.Richter, C.Bralower, T.J. . |
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Species Sphaeroidinellopsis paenedehiscens Blow 1969 |
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Diagnosis / Definition: |
Kennett & Srinivasan (1983):
Test large, low trochospiral, early chambers barely visible, ovate to smoothly rounded in equatorial periphery; chambers
three in the final whorl, inflated; sutures largely obscured by the secondary test thickening; surface covered by thick, secondary calcareous material (cortex), which restricts
the pores and provides a smooth and glossy appearance to the test; aperture an elongate umbilical opening following the line of suture between the last and first chamber of the
final whorl, bordered by a crenulated lip, which are extensions of the cortex. |
Discussion / Comments: |
Kennett & Srinivasan (1983):
Ss. paenedehiscens is distinguished from its ancestor Ss. seminulina seminulina by its more spherical and tightly coiled test and in possessing a longer primary aperture.
This species differs from Sphaeroidinella dehiscens by not having supplementary apertures on the spiral side.
Chaisson & Leckie (1993):
Remarks: This species has three chambers in the final whorl, but they are
very embracing and completely covered with cortical overgrowth so that the
test is oblate.
Similar species: Sphaeroidinellopsis seminulina may also have three
chambers in the final whorl, but its chambers are less embracing, giving the
test a more lobate equatorial outline. S. paenedehiscens evolved into
Sphaeroidinella dehiscens by developing a secondary aperture on the spiral
side. Early S. dehiscens may have only the smallest crack in the spiral side and
must be checked carefully |
Synonym list: |
Kennett & Srinivasan (1983):
Chaisson & Pearson (1997):
Chaisson & Leckie (1993):
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References: |
Blow,W.H. (1969): Late middle Eocene to Recent planktonic foraminiferal biostratigraphy. In: Proceedings of the First International Conference on Planktonic Microfossils, Geneva 1967 Vol. 1 Eds: Bronnimann, P.Renz, H.H. p. 199-422
Kennett,J. and Srinivasan,M.S. (1983): Neogene Planktonic Foraminifera - A Phylogenetic Atlas.
Chaisson,W.P. and Leckie,R.M. (1993): High-Resolution Planktonic Foraminifer Biostratigraphy of Site 806, Ontong Java Plateau (Western Equatorial Pacific). In: Proceedings of the Ocean Drilling Program, Scientific Results Vol. 130 Eds: Berger, W.H.Kroenke, L.W..Mayer, L.A..et al. p. 137-178
Chaisson,W.P. and Pearson,P.N. (1997): Planktonic foraminifer biostratigraphy at Site 925: middle Miocene–Pleistocene. In: Proceedings of the Ocean Drilling Program, Scientific Results Vol. 154 Eds: Shackleton, N.J.Curry, W.B.Richter, C.Bralower, T.J.
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