Fig. 1. Umbos and umbilical plugs. A-C: Elphidium craticulatum (Fichtel et Moll) from the Gulf of Aqaba, Red Sea. Recent. A: lateral view, SEM graph. B: peripheral view, SEM graph. C: slightly oblique axial section cutting through the symmetrical pair of umbilical plugs. Note the presence of spaces in the biumbilical shell, caused by spiral canals and funnels. Transmitted light micrograph. D-E: Amphistegina lessonii d'Orbigny from the Gulf of Aqaba, Red Sea. Recent. D: ventral view shows the stellar chamberlets overgrowing part of the ventral umbo. Incident light micrograph. E: axial section of specimen having lost the last few chambers. There is a smaller dorsal and a larger ventral umbo. F-G: Ammonia umbonata (Leroy). Dorsal and ventral views, SEM graphs. The ventral (umbilical) view exhibits a free-standing, composite umbilical plug. H-I: the umbos in porcelaneous shells may react to diagenetic processes by differences in recrystallisation that possibly indicate a differentiation in the texture of the wall in the umbonal area of the shell. Diagnostic for the involute stages in the growth of Meandropsinidae in the Upper Cretaceous of the Pyrenean Gulf. H: megalospheric Fascispira sp. from Canelles, Lerida, Northern Spain. Axial section. I: microspheric Larrazetia larrazeti (Schlumberger), center of axial section, from Bac de Grillera, Northern Spain. All scale bars 0.1 mm. a: aperture; af: apertural face; cpl: cover plate; f: foramen; fo: fossette; fpl: foramenal plate; fu: funnel; k: keel; m: mask; pust: pustules on amphisteginid face; rp: retral process; s: septum; spc: spiral canal; ub: umbo; up: umbilical plate; upl: umbilical plug. (Hottinger, 2006; fig. 77  CC/BY-NC-SA)
- according to Hottinger (2006):
SPIRAL FISSURE - deep, circular, umbilical space separating ventral chamber tips or folia from an umbilical plug, as in Ammonia.
Hottinger (2006), Illustrated glossary of terms used in foraminiferal research. Carnets de Géologie, Memoir 2, ISSN 1634-0744.
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