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Stelladinium robustum
Stelladinium robustum Zonneveld, 1997, p.334–335, pl.4, figs.8–10.
Holotype: Zonneveld, 1997, pl.4, fig.8.
Age: Holocene.
Original description (Zonneveld, 1997)
Holotype: Single Grain ARZE 22. Sample ARZE 929 (Plate IV, 8).
Type locality: Offshore Pakistan, Arabian Sea.
Etymology: With reference to its robust cell outline.
Description: Pale brown, dorsoventrally compressed, cyst with pentagonal outline. Cyst wall is formed by a smooth pedium. Epicyst triangular with a prominent apical horn. Hypocyst trapezoidal with two distinct antapical horns. Two lateral horns are present at the lateral sides of the cingulum. No additional horns are present in cingular region. Horns show no thickening of the cyst wall at their distal ends. Tabulation reflected in cingulum and archeopyle only. Archeopyle is formed by the loss of the 2a plate and is pentagonal, with enlarged sutures between plate 4' and 2a and between the intercalary and precingular plates. Operculum is often attached. Dimensions: Holotype: length (spines included) 96.4 µm; body width (spines included) 103.4 µm. Range: length (spines included) 92-125 µm (mean=108.5 µm, n=19); body width (spines included) 82-126 µm (mean= 110 µm, n= 19).
Comparison with other taxa: Stelladinium robustum differs from all other species of Stelladinium Bradford, 1975, in its much larger size. It differs from Stelladinium reductum Bint, 1988 and
Stelladinium stellatum (Wall et Dale) Reid, 1977 in having an archeopyle which is formed by the loss of the 2a plate only in contrast to the archeopyles of S. reductum and S. stellatum which are formed by the (partial loss) of plate la and 2a. Stelladinium abei Matsuoka, 1985 has a trapezoidal archeopyle whereas the archeopyle of S. robustum is pentagonal. S. robustum differs from Stelladinium reidii Bradford, 1975 in having no
additional spines along the cingulum. Thecal affinity: Wall and Dale (1968) were able to establish the relationship between Stelladinium stellatum and Protoperidinium compressum (Ab6) Balech, 1974. Because of the strong resemblance between S, robustum and S. stellatum it may be assumed that they are formed by closely related motile dinoflagellates. Stratigraphic range: Late Pleistocene-Recent (Zonneveld, 1996b; Zonneveld et al., 1996a). Environmental affinity: The highest abundance of S. robustum is in surface sediment samples of the Arabian Sea where NE monsoonal winds induce increased mixing and cooling of the upper water column (Zonneveld, 1996a,b).
Holotype: Zonneveld, 1997, pl.4, fig.8.
Age: Holocene.
Original description (Zonneveld, 1997)
Holotype: Single Grain ARZE 22. Sample ARZE 929 (Plate IV, 8).
Type locality: Offshore Pakistan, Arabian Sea.
Etymology: With reference to its robust cell outline.
Description: Pale brown, dorsoventrally compressed, cyst with pentagonal outline. Cyst wall is formed by a smooth pedium. Epicyst triangular with a prominent apical horn. Hypocyst trapezoidal with two distinct antapical horns. Two lateral horns are present at the lateral sides of the cingulum. No additional horns are present in cingular region. Horns show no thickening of the cyst wall at their distal ends. Tabulation reflected in cingulum and archeopyle only. Archeopyle is formed by the loss of the 2a plate and is pentagonal, with enlarged sutures between plate 4' and 2a and between the intercalary and precingular plates. Operculum is often attached. Dimensions: Holotype: length (spines included) 96.4 µm; body width (spines included) 103.4 µm. Range: length (spines included) 92-125 µm (mean=108.5 µm, n=19); body width (spines included) 82-126 µm (mean= 110 µm, n= 19).
Comparison with other taxa: Stelladinium robustum differs from all other species of Stelladinium Bradford, 1975, in its much larger size. It differs from Stelladinium reductum Bint, 1988 and
Stelladinium stellatum (Wall et Dale) Reid, 1977 in having an archeopyle which is formed by the loss of the 2a plate only in contrast to the archeopyles of S. reductum and S. stellatum which are formed by the (partial loss) of plate la and 2a. Stelladinium abei Matsuoka, 1985 has a trapezoidal archeopyle whereas the archeopyle of S. robustum is pentagonal. S. robustum differs from Stelladinium reidii Bradford, 1975 in having no
additional spines along the cingulum. Thecal affinity: Wall and Dale (1968) were able to establish the relationship between Stelladinium stellatum and Protoperidinium compressum (Ab6) Balech, 1974. Because of the strong resemblance between S, robustum and S. stellatum it may be assumed that they are formed by closely related motile dinoflagellates. Stratigraphic range: Late Pleistocene-Recent (Zonneveld, 1996b; Zonneveld et al., 1996a). Environmental affinity: The highest abundance of S. robustum is in surface sediment samples of the Arabian Sea where NE monsoonal winds induce increased mixing and cooling of the upper water column (Zonneveld, 1996a,b).