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Mendicodinium rugarum
Mendicodinium rugarum Piasecki, 1984
Now Hurlandsia. Originally Mendicodinium, subsequently (and now) Hurlandsia.
Holotype: Piasecki, 1984, pl.4, fig.1, text-fig.5
Age: Late Ryazanian-Early Valanginian
Original diagnosis: Piasecki 1984, p. 150-151: Mendicodinium rugarum
Proximate dinoflagellate cysts with a rounded biconical to polygonal shape in equatorial view. The cyst wall is thin and composed of one layer. The surface is apparently smooth, but a longitudinal striation may be present. SEM-analysis shows that the surface is finely sculptured (micro-rugulate). No internal wall structures are present. Paracingulum is well indicated by upfolded or thickened parasutures. In general, the paratabulation is vague but indicates a gonyaulacoid tabulation pattern: ?4", 6", ?c, 5"", lp, 1""). The epicyst is smaller than the hypocyst and the archaeopyle is formed by detachment of the epicyst; type tAtPa.
Original description: Piasecki 1984, p. 150-151: Mendicodinium rugarum
The shape of the cysts is rounded biconical to polygonal. The paracingulum marks the equatorial line and the epicyst is smaller than the hypocyst. The majority of the cysts are dorso-ventrally compressed by sediment compaction indicating an original slightly dorso-ventral flattening. During diagenesis, the thin wall is liable to strong folding and together witb a faint striation of the surface a very wrinkled appearance of the cysts is induced. The archaeopyle is formed by a suture anterior to the paracingulum. The simple operculum, the epicyst, may be attached to the hypocyst in the sulcal region, but the attachement is often ruptured along an irregular suture. The archaeopyle is of type tAtPa. The wall is composed of one layer, the autophragm, and is very thin, less than 0.5 Ám thick. Internal structures are absent and the surface appears to be smooth. Surface striation is variably evolved but when present, the striation is mainly longitudinal compared to the polar axis of the cyst. SEM analysis shows that the surface is microsculptured; the sculptural elements are smaller than the resolution of a transmission light microscope. The sculpture is micor-rugulate. Variations in the micro-sculpture, alternating smooth ridges and grooves form the coarser faint striation. The paratabulation is very incompletely reflected by low folds or thickenings of the wall and the pattern is further obscured by frequent compressional folds; the paracingulum and the parasutures of the dorsal region are best indicated. The paratabulation is interpreted as a gonyaulacoid type, the paratabulation formula being ?4", 1-6", ?c, 2-6"", lp, 1"". The holotype illustrates the most complete paratabulation recorded in this material.
Discussion: Piasecki 1984
The genus Mendicodinium was defined by Morgenroth to include proximate, non-tabulate species with indications of paracingulum - parasulcus and possessing an epicystal archaeopyle. Mendicodinium rugarum sp. nov. Deviates from the type species mainly in the surface sculpture and the presence of a weak paratabulation. M. groenlandicum (Pocock & Sarjeant) Davey, 1979 and the probably synonymous M. woodhamensis Drugg, 1978 reflect no tabulation at all.
Dimensions: 9 complete specimens were measured. The length of the cysts varies from 59 to 80 Ám, average 67 Ám. The width of the cysts varies from 60 to 74 Ám, average 66 Ám. Holotype: Pl. 4, fig 1, length 74 Ám, width 64 Ám. Paratype: Pl. 4, fig 2, length 80 Ám, width 74 Ám. Paratype: Pl. 4, fig 3, length 65 Ám, width 68 Ám.
Now Hurlandsia. Originally Mendicodinium, subsequently (and now) Hurlandsia.
Holotype: Piasecki, 1984, pl.4, fig.1, text-fig.5
Age: Late Ryazanian-Early Valanginian
Original diagnosis: Piasecki 1984, p. 150-151: Mendicodinium rugarum
Proximate dinoflagellate cysts with a rounded biconical to polygonal shape in equatorial view. The cyst wall is thin and composed of one layer. The surface is apparently smooth, but a longitudinal striation may be present. SEM-analysis shows that the surface is finely sculptured (micro-rugulate). No internal wall structures are present. Paracingulum is well indicated by upfolded or thickened parasutures. In general, the paratabulation is vague but indicates a gonyaulacoid tabulation pattern: ?4", 6", ?c, 5"", lp, 1""). The epicyst is smaller than the hypocyst and the archaeopyle is formed by detachment of the epicyst; type tAtPa.
Original description: Piasecki 1984, p. 150-151: Mendicodinium rugarum
The shape of the cysts is rounded biconical to polygonal. The paracingulum marks the equatorial line and the epicyst is smaller than the hypocyst. The majority of the cysts are dorso-ventrally compressed by sediment compaction indicating an original slightly dorso-ventral flattening. During diagenesis, the thin wall is liable to strong folding and together witb a faint striation of the surface a very wrinkled appearance of the cysts is induced. The archaeopyle is formed by a suture anterior to the paracingulum. The simple operculum, the epicyst, may be attached to the hypocyst in the sulcal region, but the attachement is often ruptured along an irregular suture. The archaeopyle is of type tAtPa. The wall is composed of one layer, the autophragm, and is very thin, less than 0.5 Ám thick. Internal structures are absent and the surface appears to be smooth. Surface striation is variably evolved but when present, the striation is mainly longitudinal compared to the polar axis of the cyst. SEM analysis shows that the surface is microsculptured; the sculptural elements are smaller than the resolution of a transmission light microscope. The sculpture is micor-rugulate. Variations in the micro-sculpture, alternating smooth ridges and grooves form the coarser faint striation. The paratabulation is very incompletely reflected by low folds or thickenings of the wall and the pattern is further obscured by frequent compressional folds; the paracingulum and the parasutures of the dorsal region are best indicated. The paratabulation is interpreted as a gonyaulacoid type, the paratabulation formula being ?4", 1-6", ?c, 2-6"", lp, 1"". The holotype illustrates the most complete paratabulation recorded in this material.
Discussion: Piasecki 1984
The genus Mendicodinium was defined by Morgenroth to include proximate, non-tabulate species with indications of paracingulum - parasulcus and possessing an epicystal archaeopyle. Mendicodinium rugarum sp. nov. Deviates from the type species mainly in the surface sculpture and the presence of a weak paratabulation. M. groenlandicum (Pocock & Sarjeant) Davey, 1979 and the probably synonymous M. woodhamensis Drugg, 1978 reflect no tabulation at all.
Dimensions: 9 complete specimens were measured. The length of the cysts varies from 59 to 80 Ám, average 67 Ám. The width of the cysts varies from 60 to 74 Ám, average 66 Ám. Holotype: Pl. 4, fig 1, length 74 Ám, width 64 Ám. Paratype: Pl. 4, fig 2, length 80 Ám, width 74 Ám. Paratype: Pl. 4, fig 3, length 65 Ám, width 68 Ám.