Nannotax Enabling nannofossil research

Description: Small circular species of Umbilicosphaera with narrow central-area. Distal shield sligtly wider than proximal shield.

Remarks: Very common. Shields often separated. Isolated distal shields show no birefringence and are almost invisible in cross-polars; but are dark in phase contrast, and so discernible. Isolated proximal shields show the reverse behaviour; they are practically invisible in phase contrast but give a weak extinction cross in cross-polars. The entire coccolith has the combined properties; and so is visible in both phase contrast and cross-polars, although due to its small size it is not obvious that the birefringence is a product of the proximal shield.

U.jafari is distinguished from U. foliosa primarily by its smaller size, but it also has a smaller central opening, and the sutures on the distal shield are straight. Because of its smaller size it is also much less strongly birefringent than U. foliosa.

Size: 3 to 4 (rarely 5) microns.

Range: NN2 to 19.

Variant:

• Umbilicosphaera petaliformis Varol, 1982 - similar but with bicylic proximal shield.

Synonymy:

• Umbilicosphaera jafari Muller 1974b p.394, pl.1/1-3, 4/43-44; Haq & Berggren 1978 p.1191, pl.1/37-37; Varol 1985 pl.1/6-10.
• Cyclococcolithus krejcigrafii Jafar 1975a p.74, pl.8/4-5.
• Cyclococcolithus stradneri Jafar 1975a p.75, pl.9/22-25
• Umbilicosphaera sibogae (Weber van Bosse) Gaarder, Haq & Berggren 1978 pl.1/41-42.
• Geminilithella jafari (Muller) Backman 1980 p.52, pl.1/16-17.
• Umbilicosphaera petaliformis Varol 1982 p.251, pl.4/7; Varol 1985 pl.1/10-11