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Labyrinthodinium truncatum ssp. modicum
Labyrinthodinium truncatum ssp. modicum De Verteuil and Norris 1996
Holotype: Plate 14, figs. 7- 12
Locus typicus: Chesapeake Bay, Calvert County, Maryland
Stratum typicum: Lower middle Miocene Plum Point Marls Member of the Calvert Formation.
Original diagnosis: de Verteuil and Norris, 1996, p. 151: Labyrinthodinium truncatum subsp. modicum
Subspecies of Labyrinthodinium truncatum Piasecki 1980 with many nontabular appendages, all less than 4.0Ám in length.
Original description: de Verteuil and Norris, 1996, p. 151: Labyrinthodinium truncatum subsp. modicum
Cysts small, proximate and spherical, with apical archeopyle Type (tA). Wall structure the same as Labyrinthodinium truncatum subsp. truncatum: homogeneous pedium and spongy luxuriae bearing membranous appendages formed from laevigate to scabrate tegillum with scattered micro-granules. Spongy luxuriae ca. 0.25 to 1.0Ám thick; virgae ca. 1.0 to 3.5Ám long, usually ca.2.0Ám, nontabular and numerous, ca. 50 to 100 on each specimen. Low septa may be present or absent at the bases of the virgae; distally virgae are crenulated, without well developed platforms. Some specimens lack recognizable virgae, having only low, evenly distributed blade-like septa (Part I, this volume; pl. 8, fig. 5).
Dimensions. Maximumdiameterexcludingvirgae 17(28)36Ám, holotype 33Ám; wall thickness 0.25 to 1.0Ám; virgae 1.0 to 3.5Ám long. Twenty-four specimens measured.
Comparison: de Verteuil and Norris, 1996, p. 151:
The new subspecies Labyrinthodinium truncatum subsp. modicum differs from Labyrinthodinium truncatum subsp. truncatum in having shorter and more numerous appendages that cannot be separated into latitudinal series.
Occurrence: Lower through middle Miocene (DN4 - DN7) in the Salisbury Embayment. In the lower part of Zone DN4, in the uppermost lower Miocene, Labyrinthodinium truncatum subsp. modicum is the only subspecies present in samples from the Salisbury Embayment. In the lower middle Miocene (DN4 - DN5) both subspecies are more or less equally present although Labyrinthodinium truncatum subsp. truncatum begins to dominate in Zone DN5. Above this level, in the Choptank Formation, Labyrinthodinium truncatum subsp. modicum is increasingly rare; it has not been recorded in the upper Miocene Saint Marys Formation.
Remarks. de Verteuil and Norris, 1996, p. 151:
Based on the stratigraphic distributions of the two subspecies of Labyrinthodinium truncatum in the Salisbury Embayment, we speculate that Labyrinthodinium truncatum subsp. modicum may be ancestral to Labyrinthodinium truncatum subsp. truncatum, and further that the genus may have evolved in the early Miocene from undescribed lower Miocene cyst morphotypes with complex proximate luxuriae and no appendages.
Holotype: Plate 14, figs. 7- 12
Locus typicus: Chesapeake Bay, Calvert County, Maryland
Stratum typicum: Lower middle Miocene Plum Point Marls Member of the Calvert Formation.
Original diagnosis: de Verteuil and Norris, 1996, p. 151: Labyrinthodinium truncatum subsp. modicum
Subspecies of Labyrinthodinium truncatum Piasecki 1980 with many nontabular appendages, all less than 4.0Ám in length.
Original description: de Verteuil and Norris, 1996, p. 151: Labyrinthodinium truncatum subsp. modicum
Cysts small, proximate and spherical, with apical archeopyle Type (tA). Wall structure the same as Labyrinthodinium truncatum subsp. truncatum: homogeneous pedium and spongy luxuriae bearing membranous appendages formed from laevigate to scabrate tegillum with scattered micro-granules. Spongy luxuriae ca. 0.25 to 1.0Ám thick; virgae ca. 1.0 to 3.5Ám long, usually ca.2.0Ám, nontabular and numerous, ca. 50 to 100 on each specimen. Low septa may be present or absent at the bases of the virgae; distally virgae are crenulated, without well developed platforms. Some specimens lack recognizable virgae, having only low, evenly distributed blade-like septa (Part I, this volume; pl. 8, fig. 5).
Dimensions. Maximumdiameterexcludingvirgae 17(28)36Ám, holotype 33Ám; wall thickness 0.25 to 1.0Ám; virgae 1.0 to 3.5Ám long. Twenty-four specimens measured.
Comparison: de Verteuil and Norris, 1996, p. 151:
The new subspecies Labyrinthodinium truncatum subsp. modicum differs from Labyrinthodinium truncatum subsp. truncatum in having shorter and more numerous appendages that cannot be separated into latitudinal series.
Occurrence: Lower through middle Miocene (DN4 - DN7) in the Salisbury Embayment. In the lower part of Zone DN4, in the uppermost lower Miocene, Labyrinthodinium truncatum subsp. modicum is the only subspecies present in samples from the Salisbury Embayment. In the lower middle Miocene (DN4 - DN5) both subspecies are more or less equally present although Labyrinthodinium truncatum subsp. truncatum begins to dominate in Zone DN5. Above this level, in the Choptank Formation, Labyrinthodinium truncatum subsp. modicum is increasingly rare; it has not been recorded in the upper Miocene Saint Marys Formation.
Remarks. de Verteuil and Norris, 1996, p. 151:
Based on the stratigraphic distributions of the two subspecies of Labyrinthodinium truncatum in the Salisbury Embayment, we speculate that Labyrinthodinium truncatum subsp. modicum may be ancestral to Labyrinthodinium truncatum subsp. truncatum, and further that the genus may have evolved in the early Miocene from undescribed lower Miocene cyst morphotypes with complex proximate luxuriae and no appendages.