Description: Closed central area. Rather heavily calcified giving irregular form, strongly crenulate margin. Occurs almost exclusively in symbiotic? associations with a centric diatomof the genus Thalassiosira. Deep photic.

Size: Coccospheres 6-10 µm; liths 2.5-4 µm.

Description: Coccoliths >6.5μm, sub-circular or broadly elliptical.

Remarks: Unambiguous Reticulofenestra disappears in the Early Quaternary but there are small reticulofenestrids without bridges though the Quaternary and a couple of extant species, including R. sessilis (see Young 2005), these are conventionally referred to Reticulofenestra but may prove to have descended from Gephyrocapsa by loss of the bridge.