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Nematosphaeropsis rigida
Nematosphaeropsis rigida Wrenn, 1988
Head and Westphal (1999, p.12) considered this species to be a questionable taxonomic junior synonym of Nematosphaeropsis balcombiana.
Holotype: Wrenn, 1988, pl.2, figs. 1-6
Locus typicus: Shell Eureka core E67- 128, deposits in the offshore of the northeast Gulf of Mexico.
Stratum typicum: Pliocene
Age: Pliocene
Diagnosis: Wrenn, 1988, p. 144, 146, 148: Nematosphaeropsis rigida
A species of Nematosphaeropsis characterized by a slightly elongate to egg-shaped central body, and solid gonal and (?) intergonal processes that are expanded proximally and distally. The processes are subrounded to subtriangular in cross-section and joined to each other distally by pairs of solid penitabular trabeculae that are rounded in cross-section. The process bases and shafts are formed by strands that arise from the central body; the bases may be perforate proximally due to incomplete fusing of these strands. Broad paraplate areas are defined by low, variably developed parasutural ridges on the central body and on the concentric trabecular shell by pairs of solid penitabular trabeculae that connect the processes distally.
Description: Wrenn, 1988, p. 144, 146, 148: Nematosphaeropsis rigida
Shape: The central body is slightly elongate to egg-shaped; the hypocyst is more broadly rounded than is the epicyst. The trabeculae connecting the ends of the processes create a subspherical concentric shell about the central body.
Phragma: The surface of the thin walled (< 1 Ám) central body is smooth to scabrate, though occasional specimens exhibit isolated, widely spaced intratabular grana. The wall of the central body gives rise to root-like structures that form the solid gonal and (?)intergonal process bases and shafts that are subrounded to subtriangular in cross-section. The process bases are often perforate because the structural strands are not completely fused to each other proximally. More than one process may develop from a single base. process bases may be connected proximally by low, variably developed ridges. Solid pairs of smooth penitabular trabeculae arise from each furcation of the process terminations. The trabeculae are subrounded in cross-section.
Paratabulation: Paratabulation is expressed to a variable degree by low parasutural ridges on the central body. The location of each parasuture also is suggested on the trabecular shell by the void between pairs of penitabular trabeculae: one penitabular trabecula resides over each of the paraplates on the central body separated by the parasuture. The paratabulation formula is 4", 6", 6C, 6"", ?p, 1"".
Paracingulum: The trace of the paracingulum is marked on the central body by low parasutural ridges and at the ends of the processes by pairs of penitabular trabeculae. Six transversely elongate, rectangular paraplates are delineated. Two pairs of parallel trabeculae encircle the dinocyst above the trace of paracingulum on the central body: one pair
of trabeculae border the anterior parasuture of the paracingulum, the other pair borders the posterior parasuture.
Parasulcus: The parasulcus is undivided proximally and distally, but it is bordered by processes bearing trabeculae.
Archeopyle: Precingular, formed by the loss of the 3" paraplate. The archeopyle is slightly reduced. The operculum is free. The trabeculum bordering the anterior parasuture of the paracingulum. adjacent to the archeopyle, is usually lost when the operculum is cast off during excystment. Other penitabular trabeculae bordering the archeopyle and
residing over the operculum may also be lost.
Dimensions: Central body length 33-41 Ám (mean 38 Ám); central body width 29-39 Ám (mean 32 Ám); overall diameter, length 49-72 Ám (mean 59 Ám); overall diameter, width 46-73 Ám (mean 54 Ám): process length 8-17 Ám. Ten specimens measured.
Comments. Wrenn, 1988, p. 144, 146, 148
Unusual specimens may bear extensive grana or nodes on the processes and trabeculae. These are considered to be aberrant forms because the trabeculae are poorly developed, incompletely connected and the unconnected ends of the trabeculae are distally rounded. These trabecular characteristics are not considered to be physical or chemical damage to the cysts, expecially in light of the presence of the unusual grana. Rare processes thought to be intergonals occur on some specimens. However, they often occur close to gonal processes and may really be basal offshoots of the latter. It is usually difficult to say with certainty.
Comparison. Wrenn, 1988, p. 144, 146, 148
In general, Nematosphaeropsis rigida sp. nov. differs from the other species of Nematosphaeropsis recognized in this paper by having clearly defined, broad paraplates, solid gonal and (?)intergonal processes that are expanded proximally and distally, and solid, round trabeculae. In addition, the process bases are usually perforate. The trabecular shell of N. rigida is more resistant to collapse than that of N. Iemniscata, apparently because the processes and trabeculae of the former are solid. In contrast, the very thin, cylindrical processes of N. lemniscata are hollow, neither expanded proximally nor distally, and are readily, and usually, distorted or collapsed onto the central body. N quinquetrum (Duxbury) Stover & Williams 1987 bears thin, solid (? round) trabeculae similar to those of N. rigida sp. nov. However, the latter species bears solid processes that are connected proximally by parasutural ridges that delimit paratabulation; N. quinquetrum lacks parasutural features on the central body.
Stratigraphic Range. Miocene-Holocene.
synonyms:
Nematosphaeropsis balcombiana auct. non Deflandre & Cookson. Wall, 1967, p. 103-104, pl. 14, fig. 17; Wall and Dale, 1967, p.350, pl.1, fig.D; Wall and Dale, 1968, p. 269-270, pl. 1, figs. 7, 8; Wall, 1971, p. 9, pl. 2, fig.4
Nematosphaeropsis sp. B., Wrenn and Kokinos, 1986,p. 188,218,pl.4,figs.5,6,pl. 17,fig. 1.
Head and Westphal (1999, p.12) considered this species to be a questionable taxonomic junior synonym of Nematosphaeropsis balcombiana.
Holotype: Wrenn, 1988, pl.2, figs. 1-6
Locus typicus: Shell Eureka core E67- 128, deposits in the offshore of the northeast Gulf of Mexico.
Stratum typicum: Pliocene
Age: Pliocene
Diagnosis: Wrenn, 1988, p. 144, 146, 148: Nematosphaeropsis rigida
A species of Nematosphaeropsis characterized by a slightly elongate to egg-shaped central body, and solid gonal and (?) intergonal processes that are expanded proximally and distally. The processes are subrounded to subtriangular in cross-section and joined to each other distally by pairs of solid penitabular trabeculae that are rounded in cross-section. The process bases and shafts are formed by strands that arise from the central body; the bases may be perforate proximally due to incomplete fusing of these strands. Broad paraplate areas are defined by low, variably developed parasutural ridges on the central body and on the concentric trabecular shell by pairs of solid penitabular trabeculae that connect the processes distally.
Description: Wrenn, 1988, p. 144, 146, 148: Nematosphaeropsis rigida
Shape: The central body is slightly elongate to egg-shaped; the hypocyst is more broadly rounded than is the epicyst. The trabeculae connecting the ends of the processes create a subspherical concentric shell about the central body.
Phragma: The surface of the thin walled (< 1 Ám) central body is smooth to scabrate, though occasional specimens exhibit isolated, widely spaced intratabular grana. The wall of the central body gives rise to root-like structures that form the solid gonal and (?)intergonal process bases and shafts that are subrounded to subtriangular in cross-section. The process bases are often perforate because the structural strands are not completely fused to each other proximally. More than one process may develop from a single base. process bases may be connected proximally by low, variably developed ridges. Solid pairs of smooth penitabular trabeculae arise from each furcation of the process terminations. The trabeculae are subrounded in cross-section.
Paratabulation: Paratabulation is expressed to a variable degree by low parasutural ridges on the central body. The location of each parasuture also is suggested on the trabecular shell by the void between pairs of penitabular trabeculae: one penitabular trabecula resides over each of the paraplates on the central body separated by the parasuture. The paratabulation formula is 4", 6", 6C, 6"", ?p, 1"".
Paracingulum: The trace of the paracingulum is marked on the central body by low parasutural ridges and at the ends of the processes by pairs of penitabular trabeculae. Six transversely elongate, rectangular paraplates are delineated. Two pairs of parallel trabeculae encircle the dinocyst above the trace of paracingulum on the central body: one pair
of trabeculae border the anterior parasuture of the paracingulum, the other pair borders the posterior parasuture.
Parasulcus: The parasulcus is undivided proximally and distally, but it is bordered by processes bearing trabeculae.
Archeopyle: Precingular, formed by the loss of the 3" paraplate. The archeopyle is slightly reduced. The operculum is free. The trabeculum bordering the anterior parasuture of the paracingulum. adjacent to the archeopyle, is usually lost when the operculum is cast off during excystment. Other penitabular trabeculae bordering the archeopyle and
residing over the operculum may also be lost.
Dimensions: Central body length 33-41 Ám (mean 38 Ám); central body width 29-39 Ám (mean 32 Ám); overall diameter, length 49-72 Ám (mean 59 Ám); overall diameter, width 46-73 Ám (mean 54 Ám): process length 8-17 Ám. Ten specimens measured.
Comments. Wrenn, 1988, p. 144, 146, 148
Unusual specimens may bear extensive grana or nodes on the processes and trabeculae. These are considered to be aberrant forms because the trabeculae are poorly developed, incompletely connected and the unconnected ends of the trabeculae are distally rounded. These trabecular characteristics are not considered to be physical or chemical damage to the cysts, expecially in light of the presence of the unusual grana. Rare processes thought to be intergonals occur on some specimens. However, they often occur close to gonal processes and may really be basal offshoots of the latter. It is usually difficult to say with certainty.
Comparison. Wrenn, 1988, p. 144, 146, 148
In general, Nematosphaeropsis rigida sp. nov. differs from the other species of Nematosphaeropsis recognized in this paper by having clearly defined, broad paraplates, solid gonal and (?)intergonal processes that are expanded proximally and distally, and solid, round trabeculae. In addition, the process bases are usually perforate. The trabecular shell of N. rigida is more resistant to collapse than that of N. Iemniscata, apparently because the processes and trabeculae of the former are solid. In contrast, the very thin, cylindrical processes of N. lemniscata are hollow, neither expanded proximally nor distally, and are readily, and usually, distorted or collapsed onto the central body. N quinquetrum (Duxbury) Stover & Williams 1987 bears thin, solid (? round) trabeculae similar to those of N. rigida sp. nov. However, the latter species bears solid processes that are connected proximally by parasutural ridges that delimit paratabulation; N. quinquetrum lacks parasutural features on the central body.
Stratigraphic Range. Miocene-Holocene.
synonyms:
Nematosphaeropsis balcombiana auct. non Deflandre & Cookson. Wall, 1967, p. 103-104, pl. 14, fig. 17; Wall and Dale, 1967, p.350, pl.1, fig.D; Wall and Dale, 1968, p. 269-270, pl. 1, figs. 7, 8; Wall, 1971, p. 9, pl. 2, fig.4
Nematosphaeropsis sp. B., Wrenn and Kokinos, 1986,p. 188,218,pl.4,figs.5,6,pl. 17,fig. 1.