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Oligosphaeridium byersense
Oligosphaeridium byersense Duane, 1997, p.134–136, pl.3, figs.1–2,4–5; pl.4, figs.1–4; text-figs.5–6.
Holotype: Duane, 1997, pl.3, fig.1; text-fig.5. Age: Valanginian.
Original description (Duane, 1997)
Holotype. P.2250.3/2 W43/2, Chester Cone Formation, Byers Peninsula, Livingston Island, South Shetland Islands,
Antarctic Peninsula; Valanginian; Plate 3, fig. 1. Paratype, P.2250.5 SEM Stub 11; Plate 4, figs. 1, 2.
Derivation of Name. From Byers Peninsula, Livingston Island, South Shetland Islands, Antarctic Peninsula.
Diagnosis. Medium-sized, skolochorate cyst, having spherical to sub-spherical central body with large, hollow,
usually stoutly tubiform, intratabular processes that are variously distally branched, aculeate or secate, to trabeculate. Paratabulation pattern is 4'; 6"; 0c; ps, 4"1 (labeled 2"1 5'"); lp; 1"". Processes in complete specimen not exceeding 17. Apical archeopyle present (Type tA), leaving cyst with zigzag margin.
Description. Skolochorate cyst of medium size possessing large, elaborate intratabular processes of variable morphology (Text-Figure 5). Sub-spherical to spherical central body composed of smooth endophragm and scabrate to granulate to very occasionally papillate periphragm. Periphragm only present in the intratabular processes.
Process bases are expanded with rare triangular-shaped depressions to the periphragm in the basal area (Plate 4, fig. 1). Process shafts vary from cylindrical, to tubiform, to buccinate, to strongly flared, at their distal margin. Processes open distally and the distal margin is developed into aculei and secae of varying length (3-16 Jim). Apical
processes are cylindrical and simple, with slightly flared distal margins and short aculei or secae. Typically, the pre,
post-cingular and antapical processes are bigger and more robust, and vary from being reduced, broad-based and
distally widening to long, slender, distally flared processes with elaborate aculeate distal margins, which are sometimes trabeculate. The antapical process is plate-centered and surrounded by possible parasutures (Plate 4, fig. 1; Text-Figure 5), suggesting that there is a sexiform antapical arrangement. There is a triangular geometry to the positioning of the lp-ps-1"" processes (X-Y-Z), which is characteristic of the genus Oligosphaeridium (Evitt, 1985) (Plate 4, fig. 1; Text-Figure 5). Rarely, the aculeate tips of neighboring postcingular processes join to form a ribbon-like,trabeculate connection between the two, denoting a parasuture (Plate 4, figs. 1,2; Text-Figures 5 and 6). There
is some indication that there may be a correlation between the number of aculei around the process tip and the triple
junctions of the paraplate which that process represents (see the 1"" process shown in Plate 4, fig. 1; Text-Figure 5). Processes are usually entire but are occasionally fenestrate along their shafts or in their distal portions. interpreted reflected paratabulation pattern is 4'; 6"; 0c; ps, 4'" (labeled 2"'-5'"); lp; 1"". However, the four postcingular processes are numbered 2"'-5"', following Evitt (1985). Apical archeopyle present (Type tA) and individual operculare
frequently found. Accessory archeopyle sutures give the cyst a zigzag margin after the archeopyle has opened. Sulcal notch is evident and is offset slightly to the left on the ventral surface.
Remarks. Oligosphaeridium byersense sp. nov. is primarily distinguished from all other species of the genus by
its varied process morphology, aculeate distal margins to the processes and occasional distal linking of its postcingular processes. Another distinguishing characteristic of the species is the presence of possible parasutures surrounding the 1"" intratabular process (Plate 4, fig. 1; Text-Figure 5). However, the "rim" surrounding the 1"" process may have been produced by mechanical pushing of the antapical process up into the central body of the cyst, as some effects of compression are obvious in this specimen. Notwithstanding this possibility, the feature of a cyst having both parasutures and intratabular processes is extremely rare (Evitt, 1985). Among all other chorate cysts, the only other species known to exhibit this feature is O. abaculum Davey 1979 (see Evitt, 1985, fig. 11.5 F-I). Only one paraplate (the antapical, 1"" paraplate) is represented by both parasutures and an intratabular process in O. byersense sp. nov., which may be used to distinguish it from O. abaculum, together with the very different process morphologies of the two species. Also, O. abaculum shows a correlation between the shape of the aculeate distal margin of the processes and the triple junctions of the paraplate that the process represents. This feature, however, is much more pronounced in O. abaculum than in O. byersense sp. nov. The process morphology of O. totum Brideaux 1971 is similar to that of O. byersense sp. nov., but the latter is distinguished by the occasional distal linking of its postcingular processes and aculeate distal margins, which may be up to 16 urn long. In
comparison to O. poculum Jain 1977,0. byersense sp. nov. has longer, more varied, and elaborate processes.
Much of the detailed morphological description of O. byersense sp. nov. has been achieved only by examination
of specimens using the SEM and by the use and interpreta-tion of the three-dimensional, stereo imaging of well preserved specimens.
Dimensions.
Central body length:48 (53.5) 62 µm
Central body width: 49 (56.2) 60 µm
Length of processes (not including aculei): 12 (22.2) 38 µm
Length of aculei: 3 (8.8) 16 µm
Median width of processes: 5 (8.5) 16 µm
Number of specimens: 15
Occurrence. P.2250.3-.11. This species has been previously recorded as Oligosphaeridium sp. A by Duane (1996).
Suggested Age. Undifferentiated Valanginian-?middle Valanginian (sensu Helby et al., 1987), Antarctic Peninsula.
(Text-Figure 4).
Holotype: Duane, 1997, pl.3, fig.1; text-fig.5. Age: Valanginian.
Original description (Duane, 1997)
Holotype. P.2250.3/2 W43/2, Chester Cone Formation, Byers Peninsula, Livingston Island, South Shetland Islands,
Antarctic Peninsula; Valanginian; Plate 3, fig. 1. Paratype, P.2250.5 SEM Stub 11; Plate 4, figs. 1, 2.
Derivation of Name. From Byers Peninsula, Livingston Island, South Shetland Islands, Antarctic Peninsula.
Diagnosis. Medium-sized, skolochorate cyst, having spherical to sub-spherical central body with large, hollow,
usually stoutly tubiform, intratabular processes that are variously distally branched, aculeate or secate, to trabeculate. Paratabulation pattern is 4'; 6"; 0c; ps, 4"1 (labeled 2"1 5'"); lp; 1"". Processes in complete specimen not exceeding 17. Apical archeopyle present (Type tA), leaving cyst with zigzag margin.
Description. Skolochorate cyst of medium size possessing large, elaborate intratabular processes of variable morphology (Text-Figure 5). Sub-spherical to spherical central body composed of smooth endophragm and scabrate to granulate to very occasionally papillate periphragm. Periphragm only present in the intratabular processes.
Process bases are expanded with rare triangular-shaped depressions to the periphragm in the basal area (Plate 4, fig. 1). Process shafts vary from cylindrical, to tubiform, to buccinate, to strongly flared, at their distal margin. Processes open distally and the distal margin is developed into aculei and secae of varying length (3-16 Jim). Apical
processes are cylindrical and simple, with slightly flared distal margins and short aculei or secae. Typically, the pre,
post-cingular and antapical processes are bigger and more robust, and vary from being reduced, broad-based and
distally widening to long, slender, distally flared processes with elaborate aculeate distal margins, which are sometimes trabeculate. The antapical process is plate-centered and surrounded by possible parasutures (Plate 4, fig. 1; Text-Figure 5), suggesting that there is a sexiform antapical arrangement. There is a triangular geometry to the positioning of the lp-ps-1"" processes (X-Y-Z), which is characteristic of the genus Oligosphaeridium (Evitt, 1985) (Plate 4, fig. 1; Text-Figure 5). Rarely, the aculeate tips of neighboring postcingular processes join to form a ribbon-like,trabeculate connection between the two, denoting a parasuture (Plate 4, figs. 1,2; Text-Figures 5 and 6). There
is some indication that there may be a correlation between the number of aculei around the process tip and the triple
junctions of the paraplate which that process represents (see the 1"" process shown in Plate 4, fig. 1; Text-Figure 5). Processes are usually entire but are occasionally fenestrate along their shafts or in their distal portions. interpreted reflected paratabulation pattern is 4'; 6"; 0c; ps, 4'" (labeled 2"'-5'"); lp; 1"". However, the four postcingular processes are numbered 2"'-5"', following Evitt (1985). Apical archeopyle present (Type tA) and individual operculare
frequently found. Accessory archeopyle sutures give the cyst a zigzag margin after the archeopyle has opened. Sulcal notch is evident and is offset slightly to the left on the ventral surface.
Remarks. Oligosphaeridium byersense sp. nov. is primarily distinguished from all other species of the genus by
its varied process morphology, aculeate distal margins to the processes and occasional distal linking of its postcingular processes. Another distinguishing characteristic of the species is the presence of possible parasutures surrounding the 1"" intratabular process (Plate 4, fig. 1; Text-Figure 5). However, the "rim" surrounding the 1"" process may have been produced by mechanical pushing of the antapical process up into the central body of the cyst, as some effects of compression are obvious in this specimen. Notwithstanding this possibility, the feature of a cyst having both parasutures and intratabular processes is extremely rare (Evitt, 1985). Among all other chorate cysts, the only other species known to exhibit this feature is O. abaculum Davey 1979 (see Evitt, 1985, fig. 11.5 F-I). Only one paraplate (the antapical, 1"" paraplate) is represented by both parasutures and an intratabular process in O. byersense sp. nov., which may be used to distinguish it from O. abaculum, together with the very different process morphologies of the two species. Also, O. abaculum shows a correlation between the shape of the aculeate distal margin of the processes and the triple junctions of the paraplate that the process represents. This feature, however, is much more pronounced in O. abaculum than in O. byersense sp. nov. The process morphology of O. totum Brideaux 1971 is similar to that of O. byersense sp. nov., but the latter is distinguished by the occasional distal linking of its postcingular processes and aculeate distal margins, which may be up to 16 urn long. In
comparison to O. poculum Jain 1977,0. byersense sp. nov. has longer, more varied, and elaborate processes.
Much of the detailed morphological description of O. byersense sp. nov. has been achieved only by examination
of specimens using the SEM and by the use and interpreta-tion of the three-dimensional, stereo imaging of well preserved specimens.
Dimensions.
Central body length:48 (53.5) 62 µm
Central body width: 49 (56.2) 60 µm
Length of processes (not including aculei): 12 (22.2) 38 µm
Length of aculei: 3 (8.8) 16 µm
Median width of processes: 5 (8.5) 16 µm
Number of specimens: 15
Occurrence. P.2250.3-.11. This species has been previously recorded as Oligosphaeridium sp. A by Duane (1996).
Suggested Age. Undifferentiated Valanginian-?middle Valanginian (sensu Helby et al., 1987), Antarctic Peninsula.
(Text-Figure 4).