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Hystrichostrogylon robustum
Hystrichostrogylon robustum Pearce, 2010, p.52–53, pl. 5, figs.4–7.
Holotype: Pearce, 2010, pl.5, figs.4–7.
Type locality and horizon. Trunch borehole, Norfolk, UK; 432.3–432.4 m, Burnham–Flamborough Chalk (undifferentiated), high Sternotaxis plana Zone (high upper Turonian).
Age: late Turonian to mid–early Campanian.
Diagnosis. A species of Hystrichostrogylon with short, robust processes.
Original description (Pearce, 2010): Medium-sized, camocavate, spiniferate, dinoflagellate cyst. The central body episome is prolate ellipsoid and th hyposome is roughly spherical to minorly oblate ellipsoid. The wall is two-layered, comprised of a thin (~0.5 μm) and smooth endophragm and a thin (~0.5 μm) and smooth periphragm, which are separated ventrally and appressed elsewhere. Short (~13 μm long), stout trifurcating gonal processes (1–2 μm wide) and up to 3 bifurcating or simple intergonal processes arise from the periphram. Bi- and trifurcating processes terminate distally with a minute (1 μm long) bifurcation. The longest processes are united proximally by a sutural crest and occur where the wall layers are appressed, and become shorter and lacking, or with much reduced, sutural crests where the wall layers are separated ventrally. As such, the paratabulation is incompletely developed. The archaeopyle is precingular (Type 1P, operculum detached) and formed by the loss of the third precingular paraplate (3"). A mid-ventral opisthopyle may be present in the periphragm.
Comparison. Hystrichostrogylon robustum sp. nov. is most closely comparable with H. membraniphorum Agelopoulos, 1964 (674, text-fig. 1–2) but differs by possessing shorter processes (although there is a slight overlap in the 13–29 μm range for H. membraniphorum), and an incomplete but more strongly developed paratabulation. Hystrichostrogylon borisii Schiøler, 1993 (106, 108, pl. 1, figs 7–9; pl. 2, figs 1–3) and H. membraniphorum granulatum Heilmann-Clausen in Heilmann-Clausen & Costa, 1989 (468, pl. 18, figs 1–3) have an ornamented endophragm, but which is smooth in H. robustum sp. nov. Differs from H. coninckii Heilmann-Clausen in Thomsen & Heilmann-Clausen, 1985 (353, 355, pl. 7, figs 9–12; text-figs 10A–F), H. clausenii Bujak, 1994 (125, 127, pl. 1, figs 4–6) and H. holohymenium Islam, 1983 (238, 240, pl. 3, figs 5–7) in the position of the pericoel.
Holotype: Pearce, 2010, pl.5, figs.4–7.
Type locality and horizon. Trunch borehole, Norfolk, UK; 432.3–432.4 m, Burnham–Flamborough Chalk (undifferentiated), high Sternotaxis plana Zone (high upper Turonian).
Age: late Turonian to mid–early Campanian.
Diagnosis. A species of Hystrichostrogylon with short, robust processes.
Original description (Pearce, 2010): Medium-sized, camocavate, spiniferate, dinoflagellate cyst. The central body episome is prolate ellipsoid and th hyposome is roughly spherical to minorly oblate ellipsoid. The wall is two-layered, comprised of a thin (~0.5 μm) and smooth endophragm and a thin (~0.5 μm) and smooth periphragm, which are separated ventrally and appressed elsewhere. Short (~13 μm long), stout trifurcating gonal processes (1–2 μm wide) and up to 3 bifurcating or simple intergonal processes arise from the periphram. Bi- and trifurcating processes terminate distally with a minute (1 μm long) bifurcation. The longest processes are united proximally by a sutural crest and occur where the wall layers are appressed, and become shorter and lacking, or with much reduced, sutural crests where the wall layers are separated ventrally. As such, the paratabulation is incompletely developed. The archaeopyle is precingular (Type 1P, operculum detached) and formed by the loss of the third precingular paraplate (3"). A mid-ventral opisthopyle may be present in the periphragm.
Comparison. Hystrichostrogylon robustum sp. nov. is most closely comparable with H. membraniphorum Agelopoulos, 1964 (674, text-fig. 1–2) but differs by possessing shorter processes (although there is a slight overlap in the 13–29 μm range for H. membraniphorum), and an incomplete but more strongly developed paratabulation. Hystrichostrogylon borisii Schiøler, 1993 (106, 108, pl. 1, figs 7–9; pl. 2, figs 1–3) and H. membraniphorum granulatum Heilmann-Clausen in Heilmann-Clausen & Costa, 1989 (468, pl. 18, figs 1–3) have an ornamented endophragm, but which is smooth in H. robustum sp. nov. Differs from H. coninckii Heilmann-Clausen in Thomsen & Heilmann-Clausen, 1985 (353, 355, pl. 7, figs 9–12; text-figs 10A–F), H. clausenii Bujak, 1994 (125, 127, pl. 1, figs 4–6) and H. holohymenium Islam, 1983 (238, 240, pl. 3, figs 5–7) in the position of the pericoel.