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Odontochitina ornata
Etymology. Latin ornatus: ornate, in reference to short sutural nipplelike and truncated processes.
Holotype. Plate 2, figs. 1–3, Borehole Bk-12, sample depth 2570, slide B, England finder H38.
Paratype. Plate 2, figs. 4–6, Borehole Bk-12, sample depth 2570, slide A, England finder R6.
Type locality. Borehole Bk-12, Bakr Oil Field, western bank to Gulf of Suez, Egypt (Fig. 1).
Type stratum. Matulla Formation, Santonian. Repository. Department of Geology, Faculty of Science, Tanta University, Egypt.
Diagnosis. Cornucavate to slightly circumcavate species of Odontochitina, having a cyst with ceratoid outline and three large horns, which are often truncated distally; smooth endophragm and granulate periphragm; tabulation expressed by the archeopyle sutures, sutural ridges and rare and short sutural nipple-like or truncated processes; apical archaeopyle type (tA), the operculum is free polyplacoid.
Dimensions. Holotype: Central body length (without operculum) 57 μm, central body width 73 μm, antapical horn length 73 μm, lateral horn length 37 μm, length of processes 2-4 μm. Range: Central body length (without operculum) 65(57)48 μm, central body width 57(67)77 μm, antapical horn length 77(67)57 μm, lateral horn length 47(22)24 μm, length of processes 2–4 μm. Specimens measured: 13.
Stratigraphic range. Santonian.
Description. Large-sized ceratioid cornucavate to slightly circumcavate dinoflagellate cyst. Central body subspherical or subrectangular in outline, compressed dorsoventrally and bears three large horns, which are blunt, but often truncated distally. Central body wall consists of two thin layers (ca. 1 μm or less): endophragm and periphragm. Endophragm smooth, periphragm granulate, rarely scabrate, but free of perforations. Horns usually wide proximally, tapering gradually, but often truncated distally. The apical and antapical horns are longer than the right lateral. Apical and antapical horns are generally straight. The antapical horn is often truncated distally or contracted with an irregular outline of the distal end. The lateral horn arising at the cingular area, often bears a small outgrowth or elbow and is curved distally towards the antapex. A corniform gonyaulacoid tabulation, is generally expressed by sutural ridges and rare short (rudimentary) sutural (mostly gonal) nipplelike, to truncated processes: four apical (4′), six precingular (6″), 6 cingular (6c), five to six postcingular (5–6″’), one posterior intercalary (1p) and one antapical plate (1″“). The sulcal plates are not expressed by sutural features. The archaeopyle apical type (tA), archeopyle sutures indicating apical and also precingular plates. The operculum is free polyplacoid. A complete specimen with an operculum has not been found in the examined material.
Comparison. Odontochitina ornata sp. nov. is an easily recognizable species. It differs from all other previously described species of the genus by its large and truncated horns (Table 1). The horns are robust and rarely folded and devoid of striae. The tabulation is reflected by the archeopyle sutures, low sutural ridges and rare short nipple-like, to truncated projections (Plate 2, figs. 7–9). These projections, which are very short (rudimentary), do not justify the assignment of the new species to Xenascus, since, according to El-Mehdawi (1998), some small spinose processes may also be present on the pericyst of Odontochitina. Recently, Niechwedowicz (2019, p. 439) also reported in its emendation of the genus Odontochitina that the periphragm of the latter is sometimes ornamented with echinae, or short spines. A similar spinose pericyst, but with more numerous spines, is also known from other species of the genus (i.e. Odontochitina spinosa Wilson, 1984). Odontochitina ornata sp. nov. differs from Xenascus plotei Below, 1982, which is considered by Below (1982, p. 22) as intermediate between Xenascus Cookson and Eisenack, 1962 and Odontochitina Deflandre, 1935 due to its rare and short processes, particularly in being tabulate and having unperforated horns and shorter (nipple-like to truncated) processes rather than longer acuminate spines. Odontochitina ornata sp. nov. is similar to Odontochitina tabulata El-Mehdawi, 1998 in possessing sutures (even faint) reflecting the tabulation pattern and by the occasional presence of the apical and antapical nipples on the endocyst (Plate 2; figs. 10–12; El- Mehdawi, 1998, pl. 1. figs. 1, 6; pl. 2, fig. 6), but differs in lacking perforations on the horns. Moreover, the horns in Odontochitina tabulata are thinner, slender and pointed rather than large and truncated in Odontochitina ornata. Xenascus wetzelii Slimani, 1996, Slimani, 2001a, 2001b, which could be re-assigned to the genus Odontochitina due to its short processes, according to the recent emendations of the genus Odontochitina (El-Mehdawi, 1998; Niechwedowicz, 2019), differs from the new species by its reticulate (rather than smooth) endophragm and its narrower and distally bifurcate (rather than large and truncated) horns. Xenascus ghanaensis Masure et al., 1998 differs from Odontochitina ornata in being atabulate and with a large pericoel around the margin of the central body in dorsoventral view and large and distally perforated horns. Moreover, the new species is generally cornucavate, with unperforated horns and with a clear corniform gonyaulacoid tabulation indicated by low sutural ridges and by sutural short nipple-like, to truncated processes.
Holotype. Plate 2, figs. 1–3, Borehole Bk-12, sample depth 2570, slide B, England finder H38.
Paratype. Plate 2, figs. 4–6, Borehole Bk-12, sample depth 2570, slide A, England finder R6.
Type locality. Borehole Bk-12, Bakr Oil Field, western bank to Gulf of Suez, Egypt (Fig. 1).
Type stratum. Matulla Formation, Santonian. Repository. Department of Geology, Faculty of Science, Tanta University, Egypt.
Diagnosis. Cornucavate to slightly circumcavate species of Odontochitina, having a cyst with ceratoid outline and three large horns, which are often truncated distally; smooth endophragm and granulate periphragm; tabulation expressed by the archeopyle sutures, sutural ridges and rare and short sutural nipple-like or truncated processes; apical archaeopyle type (tA), the operculum is free polyplacoid.
Dimensions. Holotype: Central body length (without operculum) 57 μm, central body width 73 μm, antapical horn length 73 μm, lateral horn length 37 μm, length of processes 2-4 μm. Range: Central body length (without operculum) 65(57)48 μm, central body width 57(67)77 μm, antapical horn length 77(67)57 μm, lateral horn length 47(22)24 μm, length of processes 2–4 μm. Specimens measured: 13.
Stratigraphic range. Santonian.
Description. Large-sized ceratioid cornucavate to slightly circumcavate dinoflagellate cyst. Central body subspherical or subrectangular in outline, compressed dorsoventrally and bears three large horns, which are blunt, but often truncated distally. Central body wall consists of two thin layers (ca. 1 μm or less): endophragm and periphragm. Endophragm smooth, periphragm granulate, rarely scabrate, but free of perforations. Horns usually wide proximally, tapering gradually, but often truncated distally. The apical and antapical horns are longer than the right lateral. Apical and antapical horns are generally straight. The antapical horn is often truncated distally or contracted with an irregular outline of the distal end. The lateral horn arising at the cingular area, often bears a small outgrowth or elbow and is curved distally towards the antapex. A corniform gonyaulacoid tabulation, is generally expressed by sutural ridges and rare short (rudimentary) sutural (mostly gonal) nipplelike, to truncated processes: four apical (4′), six precingular (6″), 6 cingular (6c), five to six postcingular (5–6″’), one posterior intercalary (1p) and one antapical plate (1″“). The sulcal plates are not expressed by sutural features. The archaeopyle apical type (tA), archeopyle sutures indicating apical and also precingular plates. The operculum is free polyplacoid. A complete specimen with an operculum has not been found in the examined material.
Comparison. Odontochitina ornata sp. nov. is an easily recognizable species. It differs from all other previously described species of the genus by its large and truncated horns (Table 1). The horns are robust and rarely folded and devoid of striae. The tabulation is reflected by the archeopyle sutures, low sutural ridges and rare short nipple-like, to truncated projections (Plate 2, figs. 7–9). These projections, which are very short (rudimentary), do not justify the assignment of the new species to Xenascus, since, according to El-Mehdawi (1998), some small spinose processes may also be present on the pericyst of Odontochitina. Recently, Niechwedowicz (2019, p. 439) also reported in its emendation of the genus Odontochitina that the periphragm of the latter is sometimes ornamented with echinae, or short spines. A similar spinose pericyst, but with more numerous spines, is also known from other species of the genus (i.e. Odontochitina spinosa Wilson, 1984). Odontochitina ornata sp. nov. differs from Xenascus plotei Below, 1982, which is considered by Below (1982, p. 22) as intermediate between Xenascus Cookson and Eisenack, 1962 and Odontochitina Deflandre, 1935 due to its rare and short processes, particularly in being tabulate and having unperforated horns and shorter (nipple-like to truncated) processes rather than longer acuminate spines. Odontochitina ornata sp. nov. is similar to Odontochitina tabulata El-Mehdawi, 1998 in possessing sutures (even faint) reflecting the tabulation pattern and by the occasional presence of the apical and antapical nipples on the endocyst (Plate 2; figs. 10–12; El- Mehdawi, 1998, pl. 1. figs. 1, 6; pl. 2, fig. 6), but differs in lacking perforations on the horns. Moreover, the horns in Odontochitina tabulata are thinner, slender and pointed rather than large and truncated in Odontochitina ornata. Xenascus wetzelii Slimani, 1996, Slimani, 2001a, 2001b, which could be re-assigned to the genus Odontochitina due to its short processes, according to the recent emendations of the genus Odontochitina (El-Mehdawi, 1998; Niechwedowicz, 2019), differs from the new species by its reticulate (rather than smooth) endophragm and its narrower and distally bifurcate (rather than large and truncated) horns. Xenascus ghanaensis Masure et al., 1998 differs from Odontochitina ornata in being atabulate and with a large pericoel around the margin of the central body in dorsoventral view and large and distally perforated horns. Moreover, the new species is generally cornucavate, with unperforated horns and with a clear corniform gonyaulacoid tabulation indicated by low sutural ridges and by sutural short nipple-like, to truncated processes.