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Microdinium bensonii
From Fensome et al., 2019:
Microdinium bensonii Slimani, 1994, p.25–27, pl.4, figs.1–9,14–21. Holotype: Slimani, 1994, pl.4, figs.1–4,16–17. Age: late Campanian–earliest Danian.
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Original description (Slimani, 1994):
Microdinium bensonii subsp. bensonii sp. nov. (PI.4, Fig.1-5,14-17)
Name derivation: In honor of Don G. BENSON (See synonymy).
Horizon: Turnhout -759.89 m, preparation 3, E.F. coord. P56/1.
Parazon: Turnhout -933 m, preparation 10, E.F. coord. T20.
Type locality: Turnhout -759.89 m.
Type horizon: Maastrichtian.
Synonymy:
1976: Gems B - BENSON , p. 226, pl. 14, fig. 2 - 5.
1984: Genus B de BENSON 1976 - WHITNEY , pl. 1; fig. 2, 3; text-fig. 1.
Diagnosis: Small, proximal, subspheroidal to ovoid cyst with an epicyst that is 2 to 3 times shorter than the hypocyst. It is characterized by the presence of an intratabular pericoel whose periphragm is supported by penitabular ridges approximately 1/15 of the total cyst diameter. The hypocyst has bulging lateral edges and exhibits the maximum width of the cyst. Paralabulation is indicated by penitabular ridges that delimit parasulural areas where the periphragm is apparently interrupted; it is of the partiform gonyaulacoid type and corresponds to the formula: lpr. 4', 4a. 6". 6c. 6'", 1 p. 1"", 4 - 5s. The archaeopyle is apical and intercalary of type (tAtl)a with a ventrally attached operculum.
Dimensions: Holotype: Maximum diameter: 28 µm.
Variations: Maximum diameter: 24-30 µm.
Number of specimens measured: 15.
Material: 39 specimens.
Description: The thick endophragm (1.5 to 2 µm) is smooth, the thin periphragm (about 1 µm) is smooth and transparent, the pericoel which separates them is narrow, 2 to 4 µm high. The penitabular ridges may be connected to each other in places. In the intratabular areas, the periphragm is domed and in rare cases presents small foveolae (< 1 µm in diameter in the holotype) aligned parallel to the margins of the paraplates. The antapical paraplate 1’’’’ is hexagonal while 1p is pentagonal. The organization of the hypocystal paraplates is partiform. Among the precingulate paraplates, 1" is smaller and subtriangular in outline, while 6" is rudimentary or absent. The paracingulum (4 pm wide in the holotype) is not spiral, but segmented. The parasulcus is segmented into 4 to 5 small paraplates. The archaeopyle (8 to 10 µm wide) is closed or open with a margin showing accessory sutures and an operculum comprising 1 preapical paraplate, 4 apical paraplates and 4 anterior intercalary paraplates.
Discussion: Microdinium bensonii subsp. bernerai sp. nov. is comparable to the specimens of Genus B in BENSON (1976), the same type of cyst was found by WHITNEY (1984). The attribution of this species to the genus Microdinium is possible since it has a parabulation of the partiform gonyaulacoid type, and especially an archaeopyle of type (tAtl)a. It has penitabular ridges reminiscent in appearance of the genus Alisocysta STOVER and EVITT (1978), and also of the genus Attaniodinium Zorro et al (1987), which also has polygonal paraplates. However, it is distinguished from these genera by the presence of a narrow pericoel separating the periphragm and the endophragm, by its partiform hypocystalc paralabulation, by its apical and intercalary archaeopyle, and by its smaller size.
Striatographic distribution; Turnhout: -966.50 to -759.89 m, Upper Campanian - Late Upper Maastrichtian, Early Danian. BENSON (1976) Upper Maastrichtian, base of the Monmouth Formation, Round Bay, Maryland, U.S.A. WITHNEY (1984). Upper Maastrichtian "Seven Formation" base, S. Maryland, U.S.A.
Microdinium bensonii Slimani, 1994, p.25–27, pl.4, figs.1–9,14–21. Holotype: Slimani, 1994, pl.4, figs.1–4,16–17. Age: late Campanian–earliest Danian.
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Original description (Slimani, 1994):
Microdinium bensonii subsp. bensonii sp. nov. (PI.4, Fig.1-5,14-17)
Name derivation: In honor of Don G. BENSON (See synonymy).
Horizon: Turnhout -759.89 m, preparation 3, E.F. coord. P56/1.
Parazon: Turnhout -933 m, preparation 10, E.F. coord. T20.
Type locality: Turnhout -759.89 m.
Type horizon: Maastrichtian.
Synonymy:
1976: Gems B - BENSON , p. 226, pl. 14, fig. 2 - 5.
1984: Genus B de BENSON 1976 - WHITNEY , pl. 1; fig. 2, 3; text-fig. 1.
Diagnosis: Small, proximal, subspheroidal to ovoid cyst with an epicyst that is 2 to 3 times shorter than the hypocyst. It is characterized by the presence of an intratabular pericoel whose periphragm is supported by penitabular ridges approximately 1/15 of the total cyst diameter. The hypocyst has bulging lateral edges and exhibits the maximum width of the cyst. Paralabulation is indicated by penitabular ridges that delimit parasulural areas where the periphragm is apparently interrupted; it is of the partiform gonyaulacoid type and corresponds to the formula: lpr. 4', 4a. 6". 6c. 6'", 1 p. 1"", 4 - 5s. The archaeopyle is apical and intercalary of type (tAtl)a with a ventrally attached operculum.
Dimensions: Holotype: Maximum diameter: 28 µm.
Variations: Maximum diameter: 24-30 µm.
Number of specimens measured: 15.
Material: 39 specimens.
Description: The thick endophragm (1.5 to 2 µm) is smooth, the thin periphragm (about 1 µm) is smooth and transparent, the pericoel which separates them is narrow, 2 to 4 µm high. The penitabular ridges may be connected to each other in places. In the intratabular areas, the periphragm is domed and in rare cases presents small foveolae (< 1 µm in diameter in the holotype) aligned parallel to the margins of the paraplates. The antapical paraplate 1’’’’ is hexagonal while 1p is pentagonal. The organization of the hypocystal paraplates is partiform. Among the precingulate paraplates, 1" is smaller and subtriangular in outline, while 6" is rudimentary or absent. The paracingulum (4 pm wide in the holotype) is not spiral, but segmented. The parasulcus is segmented into 4 to 5 small paraplates. The archaeopyle (8 to 10 µm wide) is closed or open with a margin showing accessory sutures and an operculum comprising 1 preapical paraplate, 4 apical paraplates and 4 anterior intercalary paraplates.
Discussion: Microdinium bensonii subsp. bernerai sp. nov. is comparable to the specimens of Genus B in BENSON (1976), the same type of cyst was found by WHITNEY (1984). The attribution of this species to the genus Microdinium is possible since it has a parabulation of the partiform gonyaulacoid type, and especially an archaeopyle of type (tAtl)a. It has penitabular ridges reminiscent in appearance of the genus Alisocysta STOVER and EVITT (1978), and also of the genus Attaniodinium Zorro et al (1987), which also has polygonal paraplates. However, it is distinguished from these genera by the presence of a narrow pericoel separating the periphragm and the endophragm, by its partiform hypocystalc paralabulation, by its apical and intercalary archaeopyle, and by its smaller size.
Striatographic distribution; Turnhout: -966.50 to -759.89 m, Upper Campanian - Late Upper Maastrichtian, Early Danian. BENSON (1976) Upper Maastrichtian, base of the Monmouth Formation, Round Bay, Maryland, U.S.A. WITHNEY (1984). Upper Maastrichtian "Seven Formation" base, S. Maryland, U.S.A.