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Systematophora silybum
Systematophora silybum Davey, 1979, p.433-434,436
Holotype: Davey, 1979, pl.50, fig.2
Paratypes: Davey, 1979
Locus typicus: Unst, Shetlands
Stratum typicum: Barremian
Original diagnosis: Davey, 1979, p. 433-436
Shape: the pericyst, excluding processes, is subspherical to ovoidal, the long axis being in the apical-antapical plane. Dorso-ventral flattening is minor. Wall: the cyst wall is apparently two-layered, the two layers being closely appressed except where the periphragm alone forms the processes. The pericyst surface is rarely smooth and is typically densely granular; the granules are concentrated in the paracingular and pandasutural areas. Processes: the processes are solid and smooth walled. Distally they terminate with an irregular bifurcation; proximally they may divide several times before joining the endocyst. Rarely neighbouring processes may be linked medially or distally. They vary in width but are approximately of equal length - typically between one quarter and one third the endocyst diameter. The processes are aligned along the paracingulum, and in the pre- and postcingular and antapical regions tend to form annulate complexes. Archeopyle: an apical archaeopyle (type A) always appears to be developed although the operculum often remains attached. The archaeopyle has a strongly zigzag margin with a moderately deep parasulcal notch. Description: Wall: the pericyst wall is approximately 0.5 µm in thickness. Smooth specimens are apparently present and although the majority of specimens are strongly granular (Pl.48, figs.7,8), the exact nature of the surface ornamentation is sometimes difficult to discern under the light microscope. The granules, which measure less than 0.5 µm in diameter, vary somewhat in size and appear to be restricted to the portions of the cyst surface outside the annulate complexes. This unusual distribution results because the smooth walled processes tend to branch proximally to give root-like extensions over the cyst surface within the annulate complexes (Pl.48, fig.7,8). A less well defined, non-granulate area sometimes surrounds the complexes and similarly results from the proximal branching of the processes. The processes vary in width from under 0.5 µm to 2 µm, are mainly either bifid distally or are broadly but irregularly capitate. Process distribution: the epicyst and hypocyst are of approximate equal size and are separated by a single alignment of processes that mark the position of the paracingulum. They are here distributed in pairs and triplets, each linear group being indicative of a single cingular paraplate. Annulate complexes occupy the pre- and postcingular and antapical regions and each indicates a single paraplate. There appear to be six precingular, five postcingular, and one antapical complex. Obvious annulate complexes or process alignments are absent in the apical and parasulcal regions.
Affinities:
Davey 1979, p. 433-436: The combination of apical archaeopyle and annulate process complexes clearly indicate that S.silyba belongs to the genus Systematophora. The simple form of the processes, however, differentiates this species from most other members of the genus, which bear complexly branching and anastomosing processes. S.areolata Klement 1960, from the Upper Jurassic, is the most similar species but differs significantly in having fewer processes which are more orderly arranged; in particular, the annulate complexes are very obvious.
Holotype: Davey, 1979, pl.50, fig.2
Paratypes: Davey, 1979
Locus typicus: Unst, Shetlands
Stratum typicum: Barremian
Original diagnosis: Davey, 1979, p. 433-436
Shape: the pericyst, excluding processes, is subspherical to ovoidal, the long axis being in the apical-antapical plane. Dorso-ventral flattening is minor. Wall: the cyst wall is apparently two-layered, the two layers being closely appressed except where the periphragm alone forms the processes. The pericyst surface is rarely smooth and is typically densely granular; the granules are concentrated in the paracingular and pandasutural areas. Processes: the processes are solid and smooth walled. Distally they terminate with an irregular bifurcation; proximally they may divide several times before joining the endocyst. Rarely neighbouring processes may be linked medially or distally. They vary in width but are approximately of equal length - typically between one quarter and one third the endocyst diameter. The processes are aligned along the paracingulum, and in the pre- and postcingular and antapical regions tend to form annulate complexes. Archeopyle: an apical archaeopyle (type A) always appears to be developed although the operculum often remains attached. The archaeopyle has a strongly zigzag margin with a moderately deep parasulcal notch. Description: Wall: the pericyst wall is approximately 0.5 µm in thickness. Smooth specimens are apparently present and although the majority of specimens are strongly granular (Pl.48, figs.7,8), the exact nature of the surface ornamentation is sometimes difficult to discern under the light microscope. The granules, which measure less than 0.5 µm in diameter, vary somewhat in size and appear to be restricted to the portions of the cyst surface outside the annulate complexes. This unusual distribution results because the smooth walled processes tend to branch proximally to give root-like extensions over the cyst surface within the annulate complexes (Pl.48, fig.7,8). A less well defined, non-granulate area sometimes surrounds the complexes and similarly results from the proximal branching of the processes. The processes vary in width from under 0.5 µm to 2 µm, are mainly either bifid distally or are broadly but irregularly capitate. Process distribution: the epicyst and hypocyst are of approximate equal size and are separated by a single alignment of processes that mark the position of the paracingulum. They are here distributed in pairs and triplets, each linear group being indicative of a single cingular paraplate. Annulate complexes occupy the pre- and postcingular and antapical regions and each indicates a single paraplate. There appear to be six precingular, five postcingular, and one antapical complex. Obvious annulate complexes or process alignments are absent in the apical and parasulcal regions.
Affinities:
Davey 1979, p. 433-436: The combination of apical archaeopyle and annulate process complexes clearly indicate that S.silyba belongs to the genus Systematophora. The simple form of the processes, however, differentiates this species from most other members of the genus, which bear complexly branching and anastomosing processes. S.areolata Klement 1960, from the Upper Jurassic, is the most similar species but differs significantly in having fewer processes which are more orderly arranged; in particular, the annulate complexes are very obvious.