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Gonyaulacysta pachyderma
Gonyaulacysta pachyderma (Deflandre, 1938) Sarjeant, 1969
Now Korystocysta. Originally Gonyaulax, subsequently Gonyaulacysta, thirdly Ctenidodinium, fourthly Ctenidodinium?, fifthly (and now) Korystocysta, sixthly Dichadogonyaulax.
Tax. sr. synonym of Leptodinium norrisii Pocock, 1972, according to Benson, 1985.
Tax. synonym of Dichadogonyaulax (now Korystocysta) kettonensis Sarjeant, 1976, according to Conway, 1990. If correct, then Gonyaulacysta pachyderma is the tax. sr. synonym.
This combination was not validly published in Sarjeant, 1966, since that author did not fully reference the basionym.
Holotype: Deflandre, 1938, pl. 7, fig. 6-7
Paratype(s):Deflandre, 1938
Locus typicus: Villers-sur-mer, Calvados, France
Stratum typicum: Oxfordian
Translation Deflandre, 1938: LPP
Original description: Deflandre, 1938, p. 176-178: Gonyaulax pachyderma
(annotated) The spheroidal thaca of this species is remarkable by the thickness of its membrane. In this respect, it present a quit prominent rigidity and the specimens are broken rather than deformed. None of my specimens is intact, but their initial shape seems to be relatively well preserved, at least in the main.
The epitheca is clearly equal to the hypoteca, of which it is separated by helicoidal transverse furrow. The longitudinal furrow reaches the apical pole on the one side and , on the other side, streches quite far on the hypotheca, probably down to the antapical plate.
The plates are delimited by strong fringed ribs, with small denticulations. The transverse furrow bears analogous fringes, generally more developed, which dissolve into a serrate denticulation, according to preservation. I think they are remains of orignally entire fringes, supported by thin trabeculae. These, being more resistant, form the spines when the continuous membrane vanished. Furthermore, one encounters intermediate aspects which support this supposition, particularly in pl. VII, fig.8, which presents a polar antapical view.
Several of the large plates present a particular ornamentation, formed by the interior ribs, parallel to their sides, which, when fully developed, form a trapezium, well illustrated in pl. VII, figs. 6 and 8. This very particular ornamentation helps to recognize isolated or broken pieces of the theca.
The epitheca has six dissimilar pre-equatorial plates, the sixth being the most reduced. Then there are four apical plates (the first of which, elongate, forms the extension of the longitudinal furow) and an intercalary plate. The fourth apical is paentagonal and very small: next to it, in line with the first apical, one finds a very weakly developed horn, indicated in black in pl. VII, fig. 6.
The tabulation of the hypoteca is less clear, because I could not see with certainty the first postequatorial plate, which is mostly reduced. Taking into account its existence, one finds six postequatorial plates, a large apical (sic), irregularly formed but with two nearly right angles, and finally, most propbably, an intercalary, situated next to the longitdinal furrow.
The membrane is entirely, but finely and irregularly puncate.
Dimensions: about 60-70 Ám in diameter and 80 Ám long.
Now Korystocysta. Originally Gonyaulax, subsequently Gonyaulacysta, thirdly Ctenidodinium, fourthly Ctenidodinium?, fifthly (and now) Korystocysta, sixthly Dichadogonyaulax.
Tax. sr. synonym of Leptodinium norrisii Pocock, 1972, according to Benson, 1985.
Tax. synonym of Dichadogonyaulax (now Korystocysta) kettonensis Sarjeant, 1976, according to Conway, 1990. If correct, then Gonyaulacysta pachyderma is the tax. sr. synonym.
This combination was not validly published in Sarjeant, 1966, since that author did not fully reference the basionym.
Holotype: Deflandre, 1938, pl. 7, fig. 6-7
Paratype(s):Deflandre, 1938
Locus typicus: Villers-sur-mer, Calvados, France
Stratum typicum: Oxfordian
Translation Deflandre, 1938: LPP
Original description: Deflandre, 1938, p. 176-178: Gonyaulax pachyderma
(annotated) The spheroidal thaca of this species is remarkable by the thickness of its membrane. In this respect, it present a quit prominent rigidity and the specimens are broken rather than deformed. None of my specimens is intact, but their initial shape seems to be relatively well preserved, at least in the main.
The epitheca is clearly equal to the hypoteca, of which it is separated by helicoidal transverse furrow. The longitudinal furrow reaches the apical pole on the one side and , on the other side, streches quite far on the hypotheca, probably down to the antapical plate.
The plates are delimited by strong fringed ribs, with small denticulations. The transverse furrow bears analogous fringes, generally more developed, which dissolve into a serrate denticulation, according to preservation. I think they are remains of orignally entire fringes, supported by thin trabeculae. These, being more resistant, form the spines when the continuous membrane vanished. Furthermore, one encounters intermediate aspects which support this supposition, particularly in pl. VII, fig.8, which presents a polar antapical view.
Several of the large plates present a particular ornamentation, formed by the interior ribs, parallel to their sides, which, when fully developed, form a trapezium, well illustrated in pl. VII, figs. 6 and 8. This very particular ornamentation helps to recognize isolated or broken pieces of the theca.
The epitheca has six dissimilar pre-equatorial plates, the sixth being the most reduced. Then there are four apical plates (the first of which, elongate, forms the extension of the longitudinal furow) and an intercalary plate. The fourth apical is paentagonal and very small: next to it, in line with the first apical, one finds a very weakly developed horn, indicated in black in pl. VII, fig. 6.
The tabulation of the hypoteca is less clear, because I could not see with certainty the first postequatorial plate, which is mostly reduced. Taking into account its existence, one finds six postequatorial plates, a large apical (sic), irregularly formed but with two nearly right angles, and finally, most propbably, an intercalary, situated next to the longitdinal furrow.
The membrane is entirely, but finely and irregularly puncate.
Dimensions: about 60-70 Ám in diameter and 80 Ám long.