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Ramidinium tridens
Ramidinium *tridens Guerstein et al., 1998, p.28–29,31–32, pl.1, figs.1–15; text-figs.2A–I,3A–I.
Holotype: Guerstein et al., 1998, pl.1, figs.4–5; text-figs.2D–E.
Age: Burdigalian–Langhian.
Original description (Guerstein et al., 1998)
Derivation of name. From the Latin tridens = trident, fork with three tines, in reference to the distal nature of the processes. The specific epithet is an noun in apposition.
Holotype. Plate 1, figures 4-5; Text-figure 2D-E. GSC specimen no. 116295, National Collection of Type Invertebrate and Plant Fossils, Geological Survey of Canada, Ottawa, Ontario, Canada; GSC Antlantic slide No P1433-10, coordinates: 84.7x2 (EF B14/1). Type locality: 108-118 feet, Corehole 16 46˚ 15'N, 49˚03'W, Grand Banks, offshore eastern Canada.
Description.
Shape. Cysts proximochorate to chorate, dorsoventrally compressed, central body lenticular. Antapical outline symmetrical or asymmetrical.
Wall relationships. Autophragm only.
Wall features. Autophragm finely ornamented, typically irregularly reticulate to rugulate (Text-fig. 3E). There are 20-26 processes, 11 or 12 on the epicyst, five to nine on the hypocyst, and four or five on the paracingulum. Processes usually gonal and intergonal, possibly sometimes intratabular; they are usually cylindrical or rounded triangular in cross section, solid and generally ending in irregular trifurcations, but they may be distally bifurcate or symmetrically expanded. Some processes may be hollow and, occasionally, taeniate processes occur that give the impression of two stems joined by a membrane. Adjacent processes are sometimes joined basally by low, possibly parasutural ridges. Delicate trabeculae occasionally connect postcingular processes.
Paratabulation. Areoligeracean paratabulation indicated on epicyst by archaeopyle sutures and location of parasutural processes. Elsewhere on central body, paratabulation indicated solely by primarily parasutural processes. Generally there is no process between paraplate 6" and the anterior sulcal paraplate.
Paracingulum. Indicated by four or five processes in gonal or intergonal positions.
Parasulcus. Position indicated anteriorly byoffset parasulcal notch. Rarely parasulcal notch medial or only slightly offset.
Archaeopyle. Apical, type (tA); operculum tetratabular, simple, free and longer transversally than dorsoventrally.
Size. Holotype: length of the central body (without operculum): 42 µm; width of the central body: 53 µm; process length: 13-19 µm. Range of 20 specimens: length of the central body (including operculum): 47 (55) 63 µm; length of the central body (without operculum): 36(41)47µm; width of the central body; 47 (55) 63 µm; process length: 9-23µm.
Comparisons. Ramidinium tridens resembles the type material of Galea twistringiensis Maier, 1959, which has a smooth wall and distally widened and regularly divided processes. Sarjeant (1983) included G. twistringiensis in synonymy with Spiniferites ramosus var. multibrevis, implying that is has a precingular rather than an apical archaeopyle. Chiropteridium galea (Maier, 1959) Sarjeant, 1983 is the species of Chiropteridium most similar to R. tridens, having processes that may be furcate or branched. However, R. tridens differs from C. galea in having processes on the epicyst that are consistently parasutural in position, isolated or united by low ridges only. Processes C. galea may be isolated, but tend to arise from four marginal meridional crests which usually are not obviously parasutural. Nevertheless, in some specimens of C. galea from the Grand Banks, meridional membranes are clearly in part parasutural, since they align with the accessory archaeopyle suture between precingular paraplates. Chiropteridium Morphotype E of Schindler (1992) also has four meridional membranes almost fully divided into hollow, distally closed and proximally interconnected processes; towards the poles these processes are more slender and distally furcated. However, Morphotype E differs from R. tridens in lacking the processes on mid-ventral and mid-dorsal surfaces and in having a distinctly granulate wall. R. tridens has an irregularly reticulate to rugulate wall and, occasionally, low proximal ridges joining adjacent processes. Enneadocysta harriii Stover & Williams, 1995 has similar process stems, but the processes are intratabular rather than parasutural and have licrate endings.
Occurence. Lower-lower Middle Miocene (Burdigalian-Langhian, as determined from palynology), Corehole 16, Grand Banks, offshore Eastern Canada.
Holotype: Guerstein et al., 1998, pl.1, figs.4–5; text-figs.2D–E.
Age: Burdigalian–Langhian.
Original description (Guerstein et al., 1998)
Derivation of name. From the Latin tridens = trident, fork with three tines, in reference to the distal nature of the processes. The specific epithet is an noun in apposition.
Holotype. Plate 1, figures 4-5; Text-figure 2D-E. GSC specimen no. 116295, National Collection of Type Invertebrate and Plant Fossils, Geological Survey of Canada, Ottawa, Ontario, Canada; GSC Antlantic slide No P1433-10, coordinates: 84.7x2 (EF B14/1). Type locality: 108-118 feet, Corehole 16 46˚ 15'N, 49˚03'W, Grand Banks, offshore eastern Canada.
Description.
Shape. Cysts proximochorate to chorate, dorsoventrally compressed, central body lenticular. Antapical outline symmetrical or asymmetrical.
Wall relationships. Autophragm only.
Wall features. Autophragm finely ornamented, typically irregularly reticulate to rugulate (Text-fig. 3E). There are 20-26 processes, 11 or 12 on the epicyst, five to nine on the hypocyst, and four or five on the paracingulum. Processes usually gonal and intergonal, possibly sometimes intratabular; they are usually cylindrical or rounded triangular in cross section, solid and generally ending in irregular trifurcations, but they may be distally bifurcate or symmetrically expanded. Some processes may be hollow and, occasionally, taeniate processes occur that give the impression of two stems joined by a membrane. Adjacent processes are sometimes joined basally by low, possibly parasutural ridges. Delicate trabeculae occasionally connect postcingular processes.
Paratabulation. Areoligeracean paratabulation indicated on epicyst by archaeopyle sutures and location of parasutural processes. Elsewhere on central body, paratabulation indicated solely by primarily parasutural processes. Generally there is no process between paraplate 6" and the anterior sulcal paraplate.
Paracingulum. Indicated by four or five processes in gonal or intergonal positions.
Parasulcus. Position indicated anteriorly byoffset parasulcal notch. Rarely parasulcal notch medial or only slightly offset.
Archaeopyle. Apical, type (tA); operculum tetratabular, simple, free and longer transversally than dorsoventrally.
Size. Holotype: length of the central body (without operculum): 42 µm; width of the central body: 53 µm; process length: 13-19 µm. Range of 20 specimens: length of the central body (including operculum): 47 (55) 63 µm; length of the central body (without operculum): 36(41)47µm; width of the central body; 47 (55) 63 µm; process length: 9-23µm.
Comparisons. Ramidinium tridens resembles the type material of Galea twistringiensis Maier, 1959, which has a smooth wall and distally widened and regularly divided processes. Sarjeant (1983) included G. twistringiensis in synonymy with Spiniferites ramosus var. multibrevis, implying that is has a precingular rather than an apical archaeopyle. Chiropteridium galea (Maier, 1959) Sarjeant, 1983 is the species of Chiropteridium most similar to R. tridens, having processes that may be furcate or branched. However, R. tridens differs from C. galea in having processes on the epicyst that are consistently parasutural in position, isolated or united by low ridges only. Processes C. galea may be isolated, but tend to arise from four marginal meridional crests which usually are not obviously parasutural. Nevertheless, in some specimens of C. galea from the Grand Banks, meridional membranes are clearly in part parasutural, since they align with the accessory archaeopyle suture between precingular paraplates. Chiropteridium Morphotype E of Schindler (1992) also has four meridional membranes almost fully divided into hollow, distally closed and proximally interconnected processes; towards the poles these processes are more slender and distally furcated. However, Morphotype E differs from R. tridens in lacking the processes on mid-ventral and mid-dorsal surfaces and in having a distinctly granulate wall. R. tridens has an irregularly reticulate to rugulate wall and, occasionally, low proximal ridges joining adjacent processes. Enneadocysta harriii Stover & Williams, 1995 has similar process stems, but the processes are intratabular rather than parasutural and have licrate endings.
Occurence. Lower-lower Middle Miocene (Burdigalian-Langhian, as determined from palynology), Corehole 16, Grand Banks, offshore Eastern Canada.