- according to Hottinger (2006):
UMBILICAL FLAP - rotaliellid extension of the umbilical chamber wall deliminating a narrow umbilicus and covering an umbilical aperture. The anterior margin may be glued to the umbilical wall of chambers in the previous whorl.
Remarks: As the term "umbilical flap" was used earlier as a synonym of "umbilical plate" in rotaliids, its revival for umbilical chamber wall extensions in Rotaliellidae (by Pavlowski et alii, 1992, fig. 1) leads to confusion and should be abandoned. Instead, umbilical chamber wall extensions in Rotaliellidae should be compared to structures in planktic foraminifera with comparably open, true umbilici and so be designated with corresponding terms.
Hottinger (2006), Illustrated glossary of terms used in foraminiferal research. Carnets de Géologie, Memoir 2, ISSN 1634-0744
Pavlowski, Zaninetti & Lee (1992), Systematic revision of tiny heterocaryotic foraminifera described by Karl GRELL in the years 1954-1979, Revue de Paléobiologie, Genève, vol. 11, N° 2, p. 385–395.