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Stelladinium denticulatum
Stelladinium denticulatum sp. nov., Uddandam et al. 2020
Holotype: Plate IV; 1, 2, Uddandam et al. 2020
Type locality: Recent sediments (0-1 cm) western Bay of Bengal
Original description:
Diagnosis:
A proximate stellate cyst with strongly developed horns. Autophragm pale brown, smooth to faintly striate. Horns are charecterised by acuminate distal terminations and
broad proximal bases. Cingulum is defined by sutures which are surmounted by small (<1 μm), distally pointed denticles. Archeopyle intercalary, offset, adnate laterally and apically, presumably representing plate 2a.
Description:
A proximate stellate cysts with with five long slender, cardinal horns at each of the angle of the ambitus. All the five horns are the extension of the central cavity and
have solid, acuminate, thickened distal terminations and broad proximal base. This species exhibits a strong dorsoventral compression. Epicyst is subtriangular/conical, where as hypocyst is trapezoidal and both have concave sides. Epicyst is smaller than the hypocyst. The antapical depression is strongly concave in nature.
Autophragm: brown, smooth with moderate thickness except for occasional discontinuous longitudinal folds.
Paratabulation: expressed in the form of archeopyle and cingulum.
Cingulum sutures: defined by denticulate margin bearing short, triangular denticles (1 μm <)
Archeopyle: large, anterior intercalary in position (type 2a), which is hexagonal in shape with rounded tips, broad posterior and a much shorter anterior margin (towards the apex), occupying much of the dorsal side of the epicyst. Archeopyle is offset to the right of the dorsoventral midline.
Operculum: is oftern adante laterally.
Tabulation: The sulcus is represented by a shallow depression and restricted to hypocyst. There are no other indications of tabulation.
Dimensions:
Cyst Body length: 65-75 μm. Cyst width: 62-65 μm. Epicyst 25-30 μm. Hypocyst 40-46 μm.
30 specimens measured
Affinities/Comparison:
S. denticulatum differs from the other four validly published Stelladinium species from its distinctive denticulate cingular ridges and cardinal horns. The occasional
supplementary spines on the cingular region of the S. reidii Bradford, 1975 are entirely different in morphology to these denticles. Furthermore, the broad proximal bases of the cardinal horns in Stelladinium denticulatum sp., nov. are unique to this species. Stelladinium abei Matsuoka, 1985 and Stelladinium reductum Bint, 1988 have short, squat polar and lateral horns. Stelladinium reidii Bradford, 1975 and Stelladinium robustum Zonneveld, 1997 also have distinctly shorter cardinal horns than Stelladinium denticulatum sp. nov. Furthermore, Stelladinium robustum Zonneveld, 1997 is significantly larger than Stelladinium denticulatum sp. nov.
Holotype: Plate IV; 1, 2, Uddandam et al. 2020
Type locality: Recent sediments (0-1 cm) western Bay of Bengal
Original description:
Diagnosis:
A proximate stellate cyst with strongly developed horns. Autophragm pale brown, smooth to faintly striate. Horns are charecterised by acuminate distal terminations and
broad proximal bases. Cingulum is defined by sutures which are surmounted by small (<1 μm), distally pointed denticles. Archeopyle intercalary, offset, adnate laterally and apically, presumably representing plate 2a.
Description:
A proximate stellate cysts with with five long slender, cardinal horns at each of the angle of the ambitus. All the five horns are the extension of the central cavity and
have solid, acuminate, thickened distal terminations and broad proximal base. This species exhibits a strong dorsoventral compression. Epicyst is subtriangular/conical, where as hypocyst is trapezoidal and both have concave sides. Epicyst is smaller than the hypocyst. The antapical depression is strongly concave in nature.
Autophragm: brown, smooth with moderate thickness except for occasional discontinuous longitudinal folds.
Paratabulation: expressed in the form of archeopyle and cingulum.
Cingulum sutures: defined by denticulate margin bearing short, triangular denticles (1 μm <)
Archeopyle: large, anterior intercalary in position (type 2a), which is hexagonal in shape with rounded tips, broad posterior and a much shorter anterior margin (towards the apex), occupying much of the dorsal side of the epicyst. Archeopyle is offset to the right of the dorsoventral midline.
Operculum: is oftern adante laterally.
Tabulation: The sulcus is represented by a shallow depression and restricted to hypocyst. There are no other indications of tabulation.
Dimensions:
Cyst Body length: 65-75 μm. Cyst width: 62-65 μm. Epicyst 25-30 μm. Hypocyst 40-46 μm.
30 specimens measured
Affinities/Comparison:
S. denticulatum differs from the other four validly published Stelladinium species from its distinctive denticulate cingular ridges and cardinal horns. The occasional
supplementary spines on the cingular region of the S. reidii Bradford, 1975 are entirely different in morphology to these denticles. Furthermore, the broad proximal bases of the cardinal horns in Stelladinium denticulatum sp., nov. are unique to this species. Stelladinium abei Matsuoka, 1985 and Stelladinium reductum Bint, 1988 have short, squat polar and lateral horns. Stelladinium reidii Bradford, 1975 and Stelladinium robustum Zonneveld, 1997 also have distinctly shorter cardinal horns than Stelladinium denticulatum sp. nov. Furthermore, Stelladinium robustum Zonneveld, 1997 is significantly larger than Stelladinium denticulatum sp. nov.