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Pyxidinopsis pastilliformis
Pyxidinopsis pastilliformis Head in Matsuoka and Head, 1992
Holotype: Head et al., 1989, pl.1, figs.9-10 (as Batiacasphaera/Cerebrocysta? Group A) and Matsuoka and Head, 1992, pl.2, figs.7-10,13
Locus typicus: Labrador Sea (ODP Hole 646B)
Stratum typicum: upper Miocene
Age: Late Miocene
Original diagnosis: Matsuoka and Head 1992, p. 168-170
Cysts small, spherical, proximate, and having two closely appressed wall layers. Wall surface is finely granulate with some fusion of adjacent granules. Operculum precingular and large, presumably formed by loss of paraplate 3" (Kofoidian notation). No accessory archeopyle sutures are developed. Operculum free. There are no other indications of paratabulation.
Dimensions. Holotype: maximum diameter, 32 µm; wall thickness, 0.5 µm. Range: maximum diameter, 27(30.0)35 µm; wall thickness, 0.4-0.8 µm. Measurements were taken with the light microscope, based on 22 specimens from three from the upper Miocene of ODP Hole 646B.
Original description: Matsuoka and Head 1992, p. 168-170
Under light microscopy (Plate 2, figs. 1-15, 18, 19), the outer wall surface bears partially fused granules (up to about 0.5 µm diameter) that may form a granulate/microvermiculate or partially microreticulate ornament (Plate 2, figs. 13-15). There is apparently no separation between wall layers, even in fragmented specimens; thus in the absence of high resolution electron microscopy, this species might be considered autophragmal. Paratabulation presumed gonyaulacoid based on the shape and presence of a precingular archeopyle. SEM observations (Plate 3, figs. 1-5, 7, 8, 10-12) reveal a wall thickness of about 0.45-0.75 µm (based on 3 specimens), with a solid, thin (0.15 µm based on one specimen) endophragm having a smooth inner surface; and a thicker periphragm consisting of short, sinuous, interconnecting muri (average width, about 0.26-0.46 µm, based on 5 specimens) that form a rugulo-reticulate pattern in plan view. Muri are rounded in cross section and seem to be supported in part, by short and narrower rods arising from the endophragm. A precingular archeopyle is confirmed by SEM observations.
Taxonomic Note: Matsuoka and Head 1992, p. 168-170
Habib (1975) erected Pyxidinopsis by monotypy for autophragmal proximate cysts that have an oval to elliptical outline in dorsal and ventral views. Although the type species, P. challengerensis Habib 1975, was described as having a reticulate wall, Habib (1975) suggested that undescribed species with granulate and vermiculate ornament could be accommodated within Pyxidinopsis. The generic placement of Pyxidinopsis pastilliformis Head sp. nov. reflects our view that the distinction between spherical and ovoidal shapes for otherwise similar cysts is not significant at the generic level.
Remarks: Matsuoka and Head 1992, p. 168-170
Specimens now attributed to P. pastilliformis were included as part of a larger group (Batiacasphaera/Cerebrocysta group A) described from upper Miocene sediments of Hole 646B in the Labrador Sea (Head et al., 1989b). This group contained small, spherical specimens with a variety of fine ornament and both precingular and, possibly, apical archeopyles. Head et al. (1989b) indicated that detailed studies including SEM analysis would be required to subdivide this group on the basis of ornament and archeopyle style. Re-examination of ODP Hole 646B material using both LM and SEM analysis has allowed the differentiation of both Batiacasphaera minuta and Pyxidinopsis pastilliformis from this complex. Furthermore, new observations (mainly with LM) show that P. pastilliformis is common in the lower part of the upper Miocene section described by Head et al. (1989b), occurring from Samples 105-646B-80X, CC through -60X, CC (nannofossil Zone NN10 through upper Zone NN11). For example, P. pastilliformis makes up about 50% of the total dinoflagellate count for Sample 105-646B-80X-2, 2-4 cm. In higher samples, specimens appeared thinner and archeopyle types were not determined with certainty. It is nevertheless possible that P. pastilliformis ranges at least to the top Miocene (Sample 105-646B-55X, CC) in Hole 646B. A preliminary re-examination of the lower through lower upper? Miocene sediments from ODP Site 645 in Baffin Bay, originally studied by Head et al. (1989c), has not revealed the presence of P. pastilliformis. Comparison. Batiacasphaera minuta comb. nov. et emend. differs from P. pastilliformis Head sp. nov. in having a microreticulate wall surface and an apical archeopyle. These two species co-occur in upper Miocene sediments from Hole 646B, but are often difficult to differentiate using archeopyle type, because the determination of the latter in both species is hindered by the frequently crumpled preservation of the cysts. The somewhat thinner wall (about 0.3 to 0.5 Ám) and microreticulate ornament of the Labrador Sea specimens now assigned to B. minuta thus help to distinguish them from P. pastilliformis in the Labrador Sea material when the archeopyle style is not clearly determinable.
Paleoecology. The abundant occurrence of P. pastilliformis in deep-water upper Miocene sediments of the Labrador Sea suggests that this species was well adapted to outer neritic or open oceanic environments.
Other Records. Specimens recorded as Tectatodinium minutum by Matsuoka and Bujak (1988), from the lower through upper Miocene of the Bering Sea; as Tectatodinium minutum by Biffi and Manum (1988) from the upper Oligocene and lower Miocene of central Italy; and as Tectatodinium simplex by Mudie (1987, pl. 3, fig. 10 only) from the upper Miocene (nannofossil Zone NN9) of DSDP Site 611, northern North Atlantic, are all comparable to P. pastilliformis in overall morphology, possession of a precingular archeopyle, and granulate ornament. Detailed analysis of surface ornamentation will be required to confirm whether these specimens are conspecific with P. pastilliformis .
Stratigraphic Range. Established occurrence: upper Miocene, Labrador Sea (Head et al.,1989b,
this study). Provisional range: upper Oligocene of Italy? (Biffi and Manum, 1988), through upper
Miocene of the Bering Sea? (Matsuoka and Bujak, 1988), northern North Atlantic? (Mudie, 1987),
and Labrador Sea (Head et al.,1989b, this study).
Holotype: Head et al., 1989, pl.1, figs.9-10 (as Batiacasphaera/Cerebrocysta? Group A) and Matsuoka and Head, 1992, pl.2, figs.7-10,13
Locus typicus: Labrador Sea (ODP Hole 646B)
Stratum typicum: upper Miocene
Age: Late Miocene
Original diagnosis: Matsuoka and Head 1992, p. 168-170
Cysts small, spherical, proximate, and having two closely appressed wall layers. Wall surface is finely granulate with some fusion of adjacent granules. Operculum precingular and large, presumably formed by loss of paraplate 3" (Kofoidian notation). No accessory archeopyle sutures are developed. Operculum free. There are no other indications of paratabulation.
Dimensions. Holotype: maximum diameter, 32 µm; wall thickness, 0.5 µm. Range: maximum diameter, 27(30.0)35 µm; wall thickness, 0.4-0.8 µm. Measurements were taken with the light microscope, based on 22 specimens from three from the upper Miocene of ODP Hole 646B.
Original description: Matsuoka and Head 1992, p. 168-170
Under light microscopy (Plate 2, figs. 1-15, 18, 19), the outer wall surface bears partially fused granules (up to about 0.5 µm diameter) that may form a granulate/microvermiculate or partially microreticulate ornament (Plate 2, figs. 13-15). There is apparently no separation between wall layers, even in fragmented specimens; thus in the absence of high resolution electron microscopy, this species might be considered autophragmal. Paratabulation presumed gonyaulacoid based on the shape and presence of a precingular archeopyle. SEM observations (Plate 3, figs. 1-5, 7, 8, 10-12) reveal a wall thickness of about 0.45-0.75 µm (based on 3 specimens), with a solid, thin (0.15 µm based on one specimen) endophragm having a smooth inner surface; and a thicker periphragm consisting of short, sinuous, interconnecting muri (average width, about 0.26-0.46 µm, based on 5 specimens) that form a rugulo-reticulate pattern in plan view. Muri are rounded in cross section and seem to be supported in part, by short and narrower rods arising from the endophragm. A precingular archeopyle is confirmed by SEM observations.
Taxonomic Note: Matsuoka and Head 1992, p. 168-170
Habib (1975) erected Pyxidinopsis by monotypy for autophragmal proximate cysts that have an oval to elliptical outline in dorsal and ventral views. Although the type species, P. challengerensis Habib 1975, was described as having a reticulate wall, Habib (1975) suggested that undescribed species with granulate and vermiculate ornament could be accommodated within Pyxidinopsis. The generic placement of Pyxidinopsis pastilliformis Head sp. nov. reflects our view that the distinction between spherical and ovoidal shapes for otherwise similar cysts is not significant at the generic level.
Remarks: Matsuoka and Head 1992, p. 168-170
Specimens now attributed to P. pastilliformis were included as part of a larger group (Batiacasphaera/Cerebrocysta group A) described from upper Miocene sediments of Hole 646B in the Labrador Sea (Head et al., 1989b). This group contained small, spherical specimens with a variety of fine ornament and both precingular and, possibly, apical archeopyles. Head et al. (1989b) indicated that detailed studies including SEM analysis would be required to subdivide this group on the basis of ornament and archeopyle style. Re-examination of ODP Hole 646B material using both LM and SEM analysis has allowed the differentiation of both Batiacasphaera minuta and Pyxidinopsis pastilliformis from this complex. Furthermore, new observations (mainly with LM) show that P. pastilliformis is common in the lower part of the upper Miocene section described by Head et al. (1989b), occurring from Samples 105-646B-80X, CC through -60X, CC (nannofossil Zone NN10 through upper Zone NN11). For example, P. pastilliformis makes up about 50% of the total dinoflagellate count for Sample 105-646B-80X-2, 2-4 cm. In higher samples, specimens appeared thinner and archeopyle types were not determined with certainty. It is nevertheless possible that P. pastilliformis ranges at least to the top Miocene (Sample 105-646B-55X, CC) in Hole 646B. A preliminary re-examination of the lower through lower upper? Miocene sediments from ODP Site 645 in Baffin Bay, originally studied by Head et al. (1989c), has not revealed the presence of P. pastilliformis. Comparison. Batiacasphaera minuta comb. nov. et emend. differs from P. pastilliformis Head sp. nov. in having a microreticulate wall surface and an apical archeopyle. These two species co-occur in upper Miocene sediments from Hole 646B, but are often difficult to differentiate using archeopyle type, because the determination of the latter in both species is hindered by the frequently crumpled preservation of the cysts. The somewhat thinner wall (about 0.3 to 0.5 Ám) and microreticulate ornament of the Labrador Sea specimens now assigned to B. minuta thus help to distinguish them from P. pastilliformis in the Labrador Sea material when the archeopyle style is not clearly determinable.
Paleoecology. The abundant occurrence of P. pastilliformis in deep-water upper Miocene sediments of the Labrador Sea suggests that this species was well adapted to outer neritic or open oceanic environments.
Other Records. Specimens recorded as Tectatodinium minutum by Matsuoka and Bujak (1988), from the lower through upper Miocene of the Bering Sea; as Tectatodinium minutum by Biffi and Manum (1988) from the upper Oligocene and lower Miocene of central Italy; and as Tectatodinium simplex by Mudie (1987, pl. 3, fig. 10 only) from the upper Miocene (nannofossil Zone NN9) of DSDP Site 611, northern North Atlantic, are all comparable to P. pastilliformis in overall morphology, possession of a precingular archeopyle, and granulate ornament. Detailed analysis of surface ornamentation will be required to confirm whether these specimens are conspecific with P. pastilliformis .
Stratigraphic Range. Established occurrence: upper Miocene, Labrador Sea (Head et al.,1989b,
this study). Provisional range: upper Oligocene of Italy? (Biffi and Manum, 1988), through upper
Miocene of the Bering Sea? (Matsuoka and Bujak, 1988), northern North Atlantic? (Mudie, 1987),
and Labrador Sea (Head et al.,1989b, this study).