Caycedoa megastypus
Set number: 601
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10µm
In mobile mount
Discoasteroides megastypus Bramlette & Sullivan, 1961
Emended by Bowman & Varol, 2021: Large (8.0–12.0μm) and circular species of Caycedoae possessing one disc and a distally flaring column. The disc is very large and displays a slight depression on the proximal side. The high column has concave peripheries with a prominent central canal. The distal side of the column has a deep depression (best seen in the side view). The disc is constructed of about 26–36 segments, but the column segments are indistinct.
In the distal/column side, the extinction lines are dextrogyre, whereas the extinction lines are laevogyre in the proximal/disc side. When viewed using a gypsum plate, the horizontal axis lies within the blue sector on the distal side, while the vertical axis lies within the blue sector on the proximal side. In plan-view, the column displays a first-order yellowish-white birefringence colour in polarised light, but the disc is non-birefringent. The disc and column are birefringent in the side-view.
Caycedoa megastypus and Caycedoa grandis differ from other species of Caycedoa by having distally flaring columns with concave peripheries. Caycedoa megastypus differs from Caycedoa grandis by having a smaller column with a smooth distal appearance.
Bowman, A. R. & Varol, O. 2021. A Taxonomic Revision of Heliolithaceae - Applications in Resolving the Problematic Calcareous Nannofossil Biostratigraphy of the Paleocene. In: M. Montenary, M. (Ed.). Calcareous nannofossil biostratigraphy of the Stratigraphy and timescales. 6: 43-223.
Bramlette, M. N. & Sullivan, F. R. 1961, Coccolithophorids and related nannoplankton of the Early Tertiary in California. Micropaleontology 7(2): 129-188.
Holotype
Discoasteroides megastypus
Bramlette & Sullivan, 1961
Late Paleocene
Lodo section, northwestern Fresno County, central California, USA