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Durotrigia omentifera
Durotrigia omentifera Feist-Burkhardt and Monteil, 2001, p.76-77, fig.7; fig.13, nos.1-3; fig.14, nos.1-5; fig.15, nos.1-5; fig.20, nos.2-6.
Holotype: Feist-Burkhardt and Monteil, 2001, fig.13, no.1; fig.20, no.4.
Age: Late Bajocian-Early Bathonian.
(Feist-Burkhardt and Monteil, 2001, p. 76-77)
Derivation of name: The specific epithet, omentifera, is derived from the Latin omentum referring to the particular aspect of the ornamentation resembling the great omentum (=epiploon), a fat containing transparent membrane which is part of the peritoneum and covers the abdominal viscera, and the verb ferre, to carry.
Description: Cyst proximate, subspherical, with a small apical bulge formed by ornamentation. Autphragm thin, ornamented by an omentum-like net constituted of laterally and vertically coalescing bulbous elements, linked distally in parasutural position. Ornamentation reduced dorsally ion the ascingular paraplates (especially 3’’, 4’’’), increasing toward the ventral face. Paraplates bordering the parasulcal zone are typically the most strongly ornamented. The omentum-like net is strongly developed in the corners of each paraplate, with very reduced lumina, giving the impression of a membrane (Fig. 15/2, 5). Several specimens show growth patterns (Fig. 13/2, Fig. 7/4, 5) and paraporoids (Fig. 13/2). Archeopyle precingular, compound, variable, formed by the loss of up to 5 precingular paraplates (1’’-5’’), opercular pieces free, adherent partially detached or adherent in place. Paratabulation completely expressed by ornamental parasutural septa with entire, non-denticulate rim. Apical cap remains generally attached to the hypocyst by an isthmus consisting of the paraplates 6’’, as, and most often, 1’’. Paraplates of the apical cap clearly differentiated. Paratabulation gonyaulacacean, formula: 2pr, 4’, 2a, 6’’, 6c, 6’’’, 1p, 1’’’’, 5s, fpi. Precingular paraplates of subequal size and stalked, exept for 3’’. Hypocystal paratabulation symmetrical sexiform. Paraplate boundaries 3’’’/4’’’and 4’’’/5’’’of the hypocyst face approximately the boundaries 2’’/3’’ and 3’’/4’’ of the epicyst (= neutral torsion of Fensome et al., 1993). Paracingulum laevorotatory, clearly indicated and subdivided by parasutural ornamentation (SEM). Parasulcus indicated by a sulcal depression (TLM, CLSM) and subdivided by parasutural ornamentation (SEM). Flagellar pore imprint is often present. L-type ventral organization.
Dimensions: Holotype: 130 µm wide at paracingulum in lateral view (partly compressed specimen in glycerine jelly slide); range in glycerine jelly slides: 110-130 µm wide at paracingulum in lateral view (partly compressed specimens), in SEM: 60-80 µm (not or partially compressed specimens).
Comparison: D. omentifera n.sp. differs from all other described Durotrigia species in its ornamentation.
Statigraphical and geographical occurrence: Feist-Burkhardt & Monteil (1998): Normandy, NW-France, Late Bajocian, Parkinsoni Zone, Densicosta Subzone to Early Bathonian, Zigzag Zone, Convergens Subzone; present study: England, Late Bajocian, Parkinsoni Zone, Densicosta Zone
Holotype: Feist-Burkhardt and Monteil, 2001, fig.13, no.1; fig.20, no.4.
Age: Late Bajocian-Early Bathonian.
(Feist-Burkhardt and Monteil, 2001, p. 76-77)
Derivation of name: The specific epithet, omentifera, is derived from the Latin omentum referring to the particular aspect of the ornamentation resembling the great omentum (=epiploon), a fat containing transparent membrane which is part of the peritoneum and covers the abdominal viscera, and the verb ferre, to carry.
Description: Cyst proximate, subspherical, with a small apical bulge formed by ornamentation. Autphragm thin, ornamented by an omentum-like net constituted of laterally and vertically coalescing bulbous elements, linked distally in parasutural position. Ornamentation reduced dorsally ion the ascingular paraplates (especially 3’’, 4’’’), increasing toward the ventral face. Paraplates bordering the parasulcal zone are typically the most strongly ornamented. The omentum-like net is strongly developed in the corners of each paraplate, with very reduced lumina, giving the impression of a membrane (Fig. 15/2, 5). Several specimens show growth patterns (Fig. 13/2, Fig. 7/4, 5) and paraporoids (Fig. 13/2). Archeopyle precingular, compound, variable, formed by the loss of up to 5 precingular paraplates (1’’-5’’), opercular pieces free, adherent partially detached or adherent in place. Paratabulation completely expressed by ornamental parasutural septa with entire, non-denticulate rim. Apical cap remains generally attached to the hypocyst by an isthmus consisting of the paraplates 6’’, as, and most often, 1’’. Paraplates of the apical cap clearly differentiated. Paratabulation gonyaulacacean, formula: 2pr, 4’, 2a, 6’’, 6c, 6’’’, 1p, 1’’’’, 5s, fpi. Precingular paraplates of subequal size and stalked, exept for 3’’. Hypocystal paratabulation symmetrical sexiform. Paraplate boundaries 3’’’/4’’’and 4’’’/5’’’of the hypocyst face approximately the boundaries 2’’/3’’ and 3’’/4’’ of the epicyst (= neutral torsion of Fensome et al., 1993). Paracingulum laevorotatory, clearly indicated and subdivided by parasutural ornamentation (SEM). Parasulcus indicated by a sulcal depression (TLM, CLSM) and subdivided by parasutural ornamentation (SEM). Flagellar pore imprint is often present. L-type ventral organization.
Dimensions: Holotype: 130 µm wide at paracingulum in lateral view (partly compressed specimen in glycerine jelly slide); range in glycerine jelly slides: 110-130 µm wide at paracingulum in lateral view (partly compressed specimens), in SEM: 60-80 µm (not or partially compressed specimens).
Comparison: D. omentifera n.sp. differs from all other described Durotrigia species in its ornamentation.
Statigraphical and geographical occurrence: Feist-Burkhardt & Monteil (1998): Normandy, NW-France, Late Bajocian, Parkinsoni Zone, Densicosta Subzone to Early Bathonian, Zigzag Zone, Convergens Subzone; present study: England, Late Bajocian, Parkinsoni Zone, Densicosta Zone