Back
Stenodinium meckelfeldense
Stenodinium *meckelfeldense (Gocht, 1969, p.15–16, pl.10, figs.12–15) Williams et al., 2015, p.314.
Holotype: Gocht, 1969, pl.10, fig.13.
Originally Wetzeliella, subsequently (and now) Stenodinium.
Age: early Eocene
Diagnosis Gocht, 1969, p.15:
Body rhomboid, convex. Horns usually long and narrow. Dextrolateral horn often fully reduced. Lateral margin notched between process bases. Processes numerous, flexible. Outer archeopyle extending distinctly beyond the inner archeopyle at the apical end.
Description Gocht, 1969, p.15-16:
This species is somewhat variable, but can be easily characterized. The flattened-convex body is rhomboid. The four horns are well expressed, long and relatively slender. The polar horns, especially the antapical horn, are usually acuminate, while the lateral horns are distally truncate or slightly retracted.
The lateral margins (including the margins of the horns) exhibit arcuate notches, with the processes rising between notches. The processes are rather long and flexible, hardly widened toward the base, and distally slightly thickened or furnished with minute spines. Dorsally, there is often a broad open zone below the pylome margin, adjoined underneath by a horizontal row of processes which may be fused into a "crest". Otherwise, no regular grouping of processes was observed. Inner body and external armor are about equally thick, mostly fragile and hyaline. Organic deposits were never found on inner body. The capsular pylome is distinctly smaller, and as in W. lunaris, the difference is always seen at the apical end, where a semilunar strip of the capsular membrane narrows the larger outer pylome. Since the outer and inner membranes are parallel in the region of the archeopyle, the size difference is not caused by optical shortening due to the greater convexity of the capsular membrane. The flagellar pore is elongate, differentiated, and oriented downward to the right.
Measurements: Holotype: length 151 µm, breadth 140 µm. Inner body 83: 75 µm. Other specimens: length 123-151 µm, breadth 119-150 µm, inner body diameter 68-85 µm. Process length 5-17 µm (usually ca. 10 µm).
Affinities: This species is closely related with W. lunaris because they have the same type of archeopyle, but it is differentiated by the more severely reduced dextral antapical horn, more distinctly notched lateral margins, the fact that the inner body is more tightly appressed on the sides, and usually by longer and more flexible processes. Moreover, in Meckelfeld it is limited to the higher Eocene strata. It could also be related to W. hyperacantha Cookson and Eisenack, but in that species the transverse body axis is longer than the longitudinal axis, and horns and processes are more sharply differentiated. On the other hand, in spite of the external resemblance, it does not seem to be directly related to W. symmetrica Weiler, a species which is frequent in the Middle Oligocene, but quite variable. The inner body of W. symmetrica is less well rounded, the processes are frequently softer and more flexible, and the pylomes- to the extent that they have been examined- smaller and congruent in both membranes.
Holotype: Gocht, 1969, pl.10, fig.13.
Originally Wetzeliella, subsequently (and now) Stenodinium.
Age: early Eocene
Diagnosis Gocht, 1969, p.15:
Body rhomboid, convex. Horns usually long and narrow. Dextrolateral horn often fully reduced. Lateral margin notched between process bases. Processes numerous, flexible. Outer archeopyle extending distinctly beyond the inner archeopyle at the apical end.
Description Gocht, 1969, p.15-16:
This species is somewhat variable, but can be easily characterized. The flattened-convex body is rhomboid. The four horns are well expressed, long and relatively slender. The polar horns, especially the antapical horn, are usually acuminate, while the lateral horns are distally truncate or slightly retracted.
The lateral margins (including the margins of the horns) exhibit arcuate notches, with the processes rising between notches. The processes are rather long and flexible, hardly widened toward the base, and distally slightly thickened or furnished with minute spines. Dorsally, there is often a broad open zone below the pylome margin, adjoined underneath by a horizontal row of processes which may be fused into a "crest". Otherwise, no regular grouping of processes was observed. Inner body and external armor are about equally thick, mostly fragile and hyaline. Organic deposits were never found on inner body. The capsular pylome is distinctly smaller, and as in W. lunaris, the difference is always seen at the apical end, where a semilunar strip of the capsular membrane narrows the larger outer pylome. Since the outer and inner membranes are parallel in the region of the archeopyle, the size difference is not caused by optical shortening due to the greater convexity of the capsular membrane. The flagellar pore is elongate, differentiated, and oriented downward to the right.
Measurements: Holotype: length 151 µm, breadth 140 µm. Inner body 83: 75 µm. Other specimens: length 123-151 µm, breadth 119-150 µm, inner body diameter 68-85 µm. Process length 5-17 µm (usually ca. 10 µm).
Affinities: This species is closely related with W. lunaris because they have the same type of archeopyle, but it is differentiated by the more severely reduced dextral antapical horn, more distinctly notched lateral margins, the fact that the inner body is more tightly appressed on the sides, and usually by longer and more flexible processes. Moreover, in Meckelfeld it is limited to the higher Eocene strata. It could also be related to W. hyperacantha Cookson and Eisenack, but in that species the transverse body axis is longer than the longitudinal axis, and horns and processes are more sharply differentiated. On the other hand, in spite of the external resemblance, it does not seem to be directly related to W. symmetrica Weiler, a species which is frequent in the Middle Oligocene, but quite variable. The inner body of W. symmetrica is less well rounded, the processes are frequently softer and more flexible, and the pylomes- to the extent that they have been examined- smaller and congruent in both membranes.