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Meiourogonyaulax planoseptata
Meiourogonyaulax planoseptata Riding, 1987
Originally (and now) Meiourogonyaulax, subsequently Lithodinia. This species is here retained in Meiourogonyaulax following the retention of the genus by Riding and Helby (2001d, p.81,83).
Holotype: Riding, 1987, fig.9, nos.9-10
Locus typicus: Nettleton Bottom Borehole, Lincolshire, England
Stratum typicum: Early Callovian
Original diagnosis: Riding, 1987, p.262
Proximate, acavate dinoflagellate cysts, ellipsoidal to elongate ellipsoidal in lateral/dorsoventral view. Autophragm smooth. Paratabulation gonyaulacacean, Kofoidian formula: 4", 6", ?6c, 6""", 1p, 1"""", 5s, paraplate boundaries bounded by smooth, continuous crests which are particularly prominent in the paracingular area and at the antapex. Paracingulum laevorotatory, with a ventral offset of one or two paracingular breadths. The parasulcus is divided into five paraplatelets. Archaeopyle apical, type (tA). Cyst insert, sexiform, with L-type ventral organisation.
Original description: Riding, 1987, p.262
A species of Meiourogonyaulax, ellipsoidal in outline with well developed gonyaulacean paratabulation (Kofoidian formula: 4",6", ?6c, 6""", 1p, 1"""", 5s) . The paraplates are bounded by smooth, featureless parasutural crests which are highest around the paracingular region and at the antapex. The exact nature of the paratabulation within the strongly laevorotatory paracingulum is not clear. By contrast, a full parasulcal paratabulation was observed, comprising an anterior parasulcal paraplatelet (as/ai), a right anterior parasulcal paraplatelet (ras/fu), a right parasulcal paraplatelet (rs/Ii), a left parasulcal paraplatelet ls/Im) and a posterior parasulcal paraplatelet (ps/Z); a prominent flagellar scar was also observed. The apical, type (4A), archaeopyle had operated in all observed specimens, only one isolated operculum was encountered.
DimensionsMinimumMeanMaximum
Overall length (excl. operculum)48.2 Ám56.6 Ám64.8 Ám
Overall breadth43.2 Ám55 .2 Ám62.2 Ám
Specimens measured: 27
Affinities:
Riding, 1987, p.262: Meiourogonyaulax planoseptata differs from all other described species of this genus by its prominent, unornamented parasutural crests. M. amlasis Below 1981 differs in its larger size, subpolygonal outline and considerably lower parasutural crests. M. bulloidea (Cookson and Eisenack 1960) Sarjeant 1969 and M. pertusa (Duxbury 1977) Below 1981 are both superficially similar, but have granulate and perforate parasutural crests respectively.
Paraplate Iu/1""" of M. planoseptata appears to be located within the parasulcus and not precisely postcingular in position, unlike some other members of the genus (e.g. M. bulloidea, M. callomoni and M. valensii).
Originally (and now) Meiourogonyaulax, subsequently Lithodinia. This species is here retained in Meiourogonyaulax following the retention of the genus by Riding and Helby (2001d, p.81,83).
Holotype: Riding, 1987, fig.9, nos.9-10
Locus typicus: Nettleton Bottom Borehole, Lincolshire, England
Stratum typicum: Early Callovian
Original diagnosis: Riding, 1987, p.262
Proximate, acavate dinoflagellate cysts, ellipsoidal to elongate ellipsoidal in lateral/dorsoventral view. Autophragm smooth. Paratabulation gonyaulacacean, Kofoidian formula: 4", 6", ?6c, 6""", 1p, 1"""", 5s, paraplate boundaries bounded by smooth, continuous crests which are particularly prominent in the paracingular area and at the antapex. Paracingulum laevorotatory, with a ventral offset of one or two paracingular breadths. The parasulcus is divided into five paraplatelets. Archaeopyle apical, type (tA). Cyst insert, sexiform, with L-type ventral organisation.
Original description: Riding, 1987, p.262
A species of Meiourogonyaulax, ellipsoidal in outline with well developed gonyaulacean paratabulation (Kofoidian formula: 4",6", ?6c, 6""", 1p, 1"""", 5s) . The paraplates are bounded by smooth, featureless parasutural crests which are highest around the paracingular region and at the antapex. The exact nature of the paratabulation within the strongly laevorotatory paracingulum is not clear. By contrast, a full parasulcal paratabulation was observed, comprising an anterior parasulcal paraplatelet (as/ai), a right anterior parasulcal paraplatelet (ras/fu), a right parasulcal paraplatelet (rs/Ii), a left parasulcal paraplatelet ls/Im) and a posterior parasulcal paraplatelet (ps/Z); a prominent flagellar scar was also observed. The apical, type (4A), archaeopyle had operated in all observed specimens, only one isolated operculum was encountered.
DimensionsMinimumMeanMaximum
Overall length (excl. operculum)48.2 Ám56.6 Ám64.8 Ám
Overall breadth43.2 Ám55 .2 Ám62.2 Ám
Specimens measured: 27
Affinities:
Riding, 1987, p.262: Meiourogonyaulax planoseptata differs from all other described species of this genus by its prominent, unornamented parasutural crests. M. amlasis Below 1981 differs in its larger size, subpolygonal outline and considerably lower parasutural crests. M. bulloidea (Cookson and Eisenack 1960) Sarjeant 1969 and M. pertusa (Duxbury 1977) Below 1981 are both superficially similar, but have granulate and perforate parasutural crests respectively.
Paraplate Iu/1""" of M. planoseptata appears to be located within the parasulcus and not precisely postcingular in position, unlike some other members of the genus (e.g. M. bulloidea, M. callomoni and M. valensii).