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Leptodinium porosum
From Fensome et al., 2019:
Leptodinium porosum (Lejeune-Carpentier, 1946, p.B193,B196; text-fig.6) Sarjeant, 1969, p.13. Emendation: Lejeune-Carpentier and Sarjeant, 1981, p.7–8, as Leptodinium porosum. Holotype: Lejeune-Carpentier, 1946, text-fig.6; Streel et al., 1977, pl.2, fig.4; Lejeune-Carpentier and Sarjeant, 1981, pl.3, figs.1–2; text-fig.4. Originally Gonyaulax (Appendix B), subsequently Gonyaulacysta (combination not validly published), thirdly (and now) Leptodinium, fourthly Leptodinium?. Questionable assignment: Stover and Evitt (1978, p.171) as a problematic species — however, Lejeune-Carpentier and Sarjeant (1981, p.7) included the species in Leptodinium without question. Jan du Chêne et al. (1986a, p.211) recommended that this name be restricted to the holotype. Age: Late Cretaceous.
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Locus typicus: Flint filling the cavity of an echinoid test (Echinocorys), Hallembaye, Belgium (= Formatie van Gulpen, of Felder, 1975).
Stratum typicum: Upper Cretaceous (Upper Senonian)
Original description: [Lejeune-Carpentier, 1946] (translated from French):
Gonyaulax porosa n. sp. (fig. 6).
Globular theca, equal in height to width (as far as the orientation of the single specimen in the preparation allows us to judge). Probably no dorsiventral flattening, but a slight depression in the ventral area. Epitheca roughly equal in size to the hypotheca and, like it, lacking horn or spines.
Levorotatory transverse groove, with ends diverging by at least twice its width. It is deep and bordered by projecting lips, giving the appearance of short, finely undulating sails reinforced
by supporting rods.
Narrow ventral area, rising slightly in the epitheca, but descending in the hypotheca to the antapical plate, which it does not, however, penetrate. Tabulation: apex impossible to fully analyze on the only available specimen. Epitheca comprising, in addition to the six precingulate elements, at least four plates, perhaps five, two of which are clearly visible through transparency on the dorsal side. The question of whether or not these plates contain intercalaries could not be resolved. Hypotheca showing the usual tabulation of Gonyaulax: 6'", 1p and 1"".
Cogal wall strongly raised at the sutures. On the plates, numerous projections rise around tiny basins in the center of which a pore opens. In places, these aligned projections simulate sutures that are sometimes difficult to distinguish from real ones.
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Emended diagnosis: Lejeune-Carpentier and Sarjeant 1981, p. 7-8
Cyst spheroidal to slightly subpolygonal in shape, without horns. Epitract and hypotract are of almost equal size and similar shape. Strong, short crests, striate or perforate and with undulose distal margins, demarcate the paraplates, those bounding the cingulum being especially prominent (though the cingulum itself is not much inset). Ventral region slightly sunken and sulcus narrow, especially in its hypotractal portion where it may be obscured from view by convergence of the crests on its boundaries. Paratabulation 4", 6", ?6c, 6"", 1p, 1"", ?s: paraplate 1"" small and elongate, it and the much larger paraplate 2"" being separated from the antapex by the large, subpentagonal posterior intercalary paraplate. Apical paraplate 4" is somewhat less long, and much broader, than the adjacent 1". Phragma ornamented generally by large pustules and a finer granulation or punctation; only the latter ornament, however, is developed on the surfaces of cingulum and sulcus.
Description: Lejeune-Carpentier and Sarjeant 1981, p. 8
Though the crests on this unique and distinctive specimen are quite prominent, they are masked by the undulose lines formed by adjacent pustules seen in profile. The posterior portion of the sulcus is masked also, by converging crests; its central and wider portion, somewhat sunken, shows flagellar marks and may be subdivided into small sulcal paraplatelets. The sulcus scarcely extends onto the epitract, its anterior prolongation being occupied by the large apical paraplate 1". The four apicals converge at the exact apex. Paraplates 2" and 3" are polygonal and of comparable size and shape, 4" somewhat larger, precingular paraplate 6" being concomitantly reduced. Paraplate 1" is also small and almost quadrate, its boundary with the sulcus poorly defined. The four remaining precingulars are all much larger. A small intercalary paraplate appears to be present at the junction of paraplates 3", 4", and 4", but its presence cannot be affirmed with complete confidence. Paraplate 1"" occupies a narrow strip bulging out a little into the sulcus; 2"" is much larger and of quadrate shape. 6"" is larger than either of these paraplates but somewhat smaller than the three other postcingulars. The posterior intercalary paraplate (lp) is unusually large, the antapical (1"") almost exactly hexagonal and of moderate size.
Dimensions: Holotype: length (in oblique view) 65 µm, maximum breadth 67 µm.
Remarks: The single specimen for which this species was erected remains the only one yet reported. It shows
no indication of an archaeopyle and, in view of the pores penetrating the pustules in the wall, resembles living motile dinoflagellates so markedly that the possibility of its being a freak inclusion into flint of a motile form cannot be excluded. However, in all other instances, the dinoflagellates preserved in flints can be shown to be cysts and, if for no better reason, we consider it most likely that this also is a cyst. Since, in all features save the absence of an archaeopyle, this species accords with the generic diagnosis of Leptodinium, it is assigned to that genus with fair confidence. However, the discovery of future specimens must be awaited before the nature of this species can be finally decided.
The specific diagnosis is emended to include reference to the apical paraplates and to specify more exactly the shape of the ventral hypotractal paraplates.
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Leptodinium porosum (Lejeune-Carpentier, 1946, p.B193,B196; text-fig.6) Sarjeant, 1969, p.13. Emendation: Lejeune-Carpentier and Sarjeant, 1981, p.7–8, as Leptodinium porosum. Holotype: Lejeune-Carpentier, 1946, text-fig.6; Streel et al., 1977, pl.2, fig.4; Lejeune-Carpentier and Sarjeant, 1981, pl.3, figs.1–2; text-fig.4. Originally Gonyaulax (Appendix B), subsequently Gonyaulacysta (combination not validly published), thirdly (and now) Leptodinium, fourthly Leptodinium?. Questionable assignment: Stover and Evitt (1978, p.171) as a problematic species — however, Lejeune-Carpentier and Sarjeant (1981, p.7) included the species in Leptodinium without question. Jan du Chêne et al. (1986a, p.211) recommended that this name be restricted to the holotype. Age: Late Cretaceous.
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Locus typicus: Flint filling the cavity of an echinoid test (Echinocorys), Hallembaye, Belgium (= Formatie van Gulpen, of Felder, 1975).
Stratum typicum: Upper Cretaceous (Upper Senonian)
Original description: [Lejeune-Carpentier, 1946] (translated from French):
Gonyaulax porosa n. sp. (fig. 6).
Globular theca, equal in height to width (as far as the orientation of the single specimen in the preparation allows us to judge). Probably no dorsiventral flattening, but a slight depression in the ventral area. Epitheca roughly equal in size to the hypotheca and, like it, lacking horn or spines.
Levorotatory transverse groove, with ends diverging by at least twice its width. It is deep and bordered by projecting lips, giving the appearance of short, finely undulating sails reinforced
by supporting rods.
Narrow ventral area, rising slightly in the epitheca, but descending in the hypotheca to the antapical plate, which it does not, however, penetrate. Tabulation: apex impossible to fully analyze on the only available specimen. Epitheca comprising, in addition to the six precingulate elements, at least four plates, perhaps five, two of which are clearly visible through transparency on the dorsal side. The question of whether or not these plates contain intercalaries could not be resolved. Hypotheca showing the usual tabulation of Gonyaulax: 6'", 1p and 1"".
Cogal wall strongly raised at the sutures. On the plates, numerous projections rise around tiny basins in the center of which a pore opens. In places, these aligned projections simulate sutures that are sometimes difficult to distinguish from real ones.
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Emended diagnosis: Lejeune-Carpentier and Sarjeant 1981, p. 7-8
Cyst spheroidal to slightly subpolygonal in shape, without horns. Epitract and hypotract are of almost equal size and similar shape. Strong, short crests, striate or perforate and with undulose distal margins, demarcate the paraplates, those bounding the cingulum being especially prominent (though the cingulum itself is not much inset). Ventral region slightly sunken and sulcus narrow, especially in its hypotractal portion where it may be obscured from view by convergence of the crests on its boundaries. Paratabulation 4", 6", ?6c, 6"", 1p, 1"", ?s: paraplate 1"" small and elongate, it and the much larger paraplate 2"" being separated from the antapex by the large, subpentagonal posterior intercalary paraplate. Apical paraplate 4" is somewhat less long, and much broader, than the adjacent 1". Phragma ornamented generally by large pustules and a finer granulation or punctation; only the latter ornament, however, is developed on the surfaces of cingulum and sulcus.
Description: Lejeune-Carpentier and Sarjeant 1981, p. 8
Though the crests on this unique and distinctive specimen are quite prominent, they are masked by the undulose lines formed by adjacent pustules seen in profile. The posterior portion of the sulcus is masked also, by converging crests; its central and wider portion, somewhat sunken, shows flagellar marks and may be subdivided into small sulcal paraplatelets. The sulcus scarcely extends onto the epitract, its anterior prolongation being occupied by the large apical paraplate 1". The four apicals converge at the exact apex. Paraplates 2" and 3" are polygonal and of comparable size and shape, 4" somewhat larger, precingular paraplate 6" being concomitantly reduced. Paraplate 1" is also small and almost quadrate, its boundary with the sulcus poorly defined. The four remaining precingulars are all much larger. A small intercalary paraplate appears to be present at the junction of paraplates 3", 4", and 4", but its presence cannot be affirmed with complete confidence. Paraplate 1"" occupies a narrow strip bulging out a little into the sulcus; 2"" is much larger and of quadrate shape. 6"" is larger than either of these paraplates but somewhat smaller than the three other postcingulars. The posterior intercalary paraplate (lp) is unusually large, the antapical (1"") almost exactly hexagonal and of moderate size.
Dimensions: Holotype: length (in oblique view) 65 µm, maximum breadth 67 µm.
Remarks: The single specimen for which this species was erected remains the only one yet reported. It shows
no indication of an archaeopyle and, in view of the pores penetrating the pustules in the wall, resembles living motile dinoflagellates so markedly that the possibility of its being a freak inclusion into flint of a motile form cannot be excluded. However, in all other instances, the dinoflagellates preserved in flints can be shown to be cysts and, if for no better reason, we consider it most likely that this also is a cyst. Since, in all features save the absence of an archaeopyle, this species accords with the generic diagnosis of Leptodinium, it is assigned to that genus with fair confidence. However, the discovery of future specimens must be awaited before the nature of this species can be finally decided.
The specific diagnosis is emended to include reference to the apical paraplates and to specify more exactly the shape of the ventral hypotractal paraplates.
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