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Nematosphaeropsis downiei
Nematosphaeropsis downiei Brown, 1986
Holotype: Brown, 1986, pl. 1, fig. 1-2
Locus typicus: DSDP Leg 80, Hole 484A, northern part Bay of Biscay, eastern N Atlantic
Stratum typicum: Early Miocene
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G.L. Williams short notes on species, Mesozoic-Cenozoic dinocyst course, Urbino, Italy, May 17-22, 1999 - LPP VIEWER CD-ROM 99.5.
Nematosphaeropsis downiei Brown, 1986. According to Brown (1986), Nematosphaeropsis downiei has a faintly granular, ovoidal to subspheroidal central body. The gonal and sutural processes are linked distally by thin-walled, broad membranous trabeculae. Parasutural features are evident in places on the central body. Occasionally the processes may be linked by parasutural features on the cyst body. All processes expand distally into two trabeculae linked by a thin membrane which joins adjacent processes. The overall length of the processes is 20-30 µm and is of constant length on the same specimen. Size: overall length 59-95 µm, overall width 45.5-88 µm, central body length 41.5-65 µm, width 36.5-60 µm.
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Original description: Brown, 1986, p. 7-10
Diagnosis: A species of Nematosphaeropsis with a faintly granular, ovoidal to subspherical central body. The gonal and sutural processes are linked distally by thin-walled, broad, membranous trabeculae. Parasutural features are evident in places on the central body.
Description: Chorate cyst with ovoidal to subspherical central bodies. Sutural and gonal processes linked together by distal trabeculae to form an outer sphere. A single wall layer is visible in transmitted light, the surface is regularly granular. No internal structure is visible in the wall. Gonal and sutural processes are present, occasionally linked by parasutural features on the surface of the inner body. The processes may be hollow, but due to compression and folding of the specimens this is not certain. All processes expand distally into two trabeculae linked by a thin membrane which join adjacent processes. The overall length of the processes is usually between 20 Ám and 30 Ám, and consistently the same on each specimen, to such an extent that the outer ovoid formed by the trabeculae is a constant distance from the central body. The archaeopyle (Type P) is interpreted as being formed by the loss of one precingular paraplate (3'') and the operculum is usually free. The paratabulation formula cannot be accurately determined, however indications from the course of the trabeculae between processes, where visible, would suggest a typical Gonyaulacacean formula of: 3-4', 5-6'', 6c, 5-6''', 1p, 1''''. This paratabulation is not clearly visible in the specimens obtained for this study since all had undergone some degree of compression. The paracingulum appears to be slightly helicoidal.
Dimensions: Holotype: overall length 95 Ám; overall breadth 88 Ám, central body length 65 Ám, central body width 60 Ám. Process length 28-30 Ám. Range: overall length 95(82.2)59 Ám, overall breadth 88(71.1)45.5 Ám, central body length 65(53.8)41.5 Ám, central body breadth 60(45.8)36.5 Ám.
Affinities:
Brown, 1986
Remarks: N. downiei sp. nov. differs from previously described species of the genus in its greater size, both of central body and the length of the processes. Similar forms have been recorded from the Early Miocene of Italy (Powell, 1983, thesis) although these lack granulate ornament on the central body. N. downiei sp. nov. has certain structural similarities to N. aquaeducta Piasecki, although the latter is much smaller and has processes which are shorter in proportion to the central body diameter. The concave nature of the trabeculae occurring in N. aquaducta can also be discerned in some specimens of N. downiei sp. nov. Similarities exist on a superficial level with several species of other genera. Balteocysta perforata (Davey, 1978) Wilson and Clowes, 1980 differs in that it possesses only intratabular paracingular processes. Arachnodinium antarcticum Wilson and Clowes, 1982 superficially resembles N. downiei sp. nov. but has an apical rather than precingular archeopyle, and possesses only precingular and antapical processes. N. downiei sp. nov. was recorded as Nematosphaeropsis sp. A by Brown and Downie (1984), however no description was included.
Holotype: Brown, 1986, pl. 1, fig. 1-2
Locus typicus: DSDP Leg 80, Hole 484A, northern part Bay of Biscay, eastern N Atlantic
Stratum typicum: Early Miocene
--------------------------------------------------
G.L. Williams short notes on species, Mesozoic-Cenozoic dinocyst course, Urbino, Italy, May 17-22, 1999 - LPP VIEWER CD-ROM 99.5.
Nematosphaeropsis downiei Brown, 1986. According to Brown (1986), Nematosphaeropsis downiei has a faintly granular, ovoidal to subspheroidal central body. The gonal and sutural processes are linked distally by thin-walled, broad membranous trabeculae. Parasutural features are evident in places on the central body. Occasionally the processes may be linked by parasutural features on the cyst body. All processes expand distally into two trabeculae linked by a thin membrane which joins adjacent processes. The overall length of the processes is 20-30 µm and is of constant length on the same specimen. Size: overall length 59-95 µm, overall width 45.5-88 µm, central body length 41.5-65 µm, width 36.5-60 µm.
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Original description: Brown, 1986, p. 7-10
Diagnosis: A species of Nematosphaeropsis with a faintly granular, ovoidal to subspherical central body. The gonal and sutural processes are linked distally by thin-walled, broad, membranous trabeculae. Parasutural features are evident in places on the central body.
Description: Chorate cyst with ovoidal to subspherical central bodies. Sutural and gonal processes linked together by distal trabeculae to form an outer sphere. A single wall layer is visible in transmitted light, the surface is regularly granular. No internal structure is visible in the wall. Gonal and sutural processes are present, occasionally linked by parasutural features on the surface of the inner body. The processes may be hollow, but due to compression and folding of the specimens this is not certain. All processes expand distally into two trabeculae linked by a thin membrane which join adjacent processes. The overall length of the processes is usually between 20 Ám and 30 Ám, and consistently the same on each specimen, to such an extent that the outer ovoid formed by the trabeculae is a constant distance from the central body. The archaeopyle (Type P) is interpreted as being formed by the loss of one precingular paraplate (3'') and the operculum is usually free. The paratabulation formula cannot be accurately determined, however indications from the course of the trabeculae between processes, where visible, would suggest a typical Gonyaulacacean formula of: 3-4', 5-6'', 6c, 5-6''', 1p, 1''''. This paratabulation is not clearly visible in the specimens obtained for this study since all had undergone some degree of compression. The paracingulum appears to be slightly helicoidal.
Dimensions: Holotype: overall length 95 Ám; overall breadth 88 Ám, central body length 65 Ám, central body width 60 Ám. Process length 28-30 Ám. Range: overall length 95(82.2)59 Ám, overall breadth 88(71.1)45.5 Ám, central body length 65(53.8)41.5 Ám, central body breadth 60(45.8)36.5 Ám.
Affinities:
Brown, 1986
Remarks: N. downiei sp. nov. differs from previously described species of the genus in its greater size, both of central body and the length of the processes. Similar forms have been recorded from the Early Miocene of Italy (Powell, 1983, thesis) although these lack granulate ornament on the central body. N. downiei sp. nov. has certain structural similarities to N. aquaeducta Piasecki, although the latter is much smaller and has processes which are shorter in proportion to the central body diameter. The concave nature of the trabeculae occurring in N. aquaducta can also be discerned in some specimens of N. downiei sp. nov. Similarities exist on a superficial level with several species of other genera. Balteocysta perforata (Davey, 1978) Wilson and Clowes, 1980 differs in that it possesses only intratabular paracingular processes. Arachnodinium antarcticum Wilson and Clowes, 1982 superficially resembles N. downiei sp. nov. but has an apical rather than precingular archeopyle, and possesses only precingular and antapical processes. N. downiei sp. nov. was recorded as Nematosphaeropsis sp. A by Brown and Downie (1984), however no description was included.