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Nannoceratopsis spiculata
Nannoceratopsis spiculata Stover, 1966
Holotype: Stover, 1966, pl.8, fig.1A-D
Locus typicus: Inferior Oolite Formation (middle part), Calvados, France
Stratum typicum: Bajocian-Bathonian
Original diagnosis: Stover, 1966, p.42
Non-tabulate fossil dinoflagellates witll a laterally flattened test, an acute apical end and two prominent antapical horns ol nearly equal size. Outline subtriangular; epithecal portion of test small; girdle well developed, especially along its right lateral and dorsal surfaces; hypotilecal portion much larger than epithecal portion of test. Right lateral surface of hypothecal portion of test longer antapically than left lateral surface. Dorsal and ventral surfaces narrow and usually bordered by low lateral ridges. Surface clear or finely to coarsely areolate. Mean length, 96 Ám; ean width, 55 Ám.
Original description: Stover, 1966, p.42
Test composed of a minute epithecal portion and a large hypothecal portion separated by a relatively high subapical girdle. In lateral view, the test is subtriangular in outline with an acute apex straight to convex sides and a deeply concave base. Narrow dorsal and ventral surfaces are bounded by lateral ridges. Specimens measure 81 to 102 Ám in length and 50 to 64 Ám in width across their widest part.
Epithecal portion of test is small, 4 to 8 Ám high and more or less conical, but with a truncated left lateral surface. A basal ridge or thickening occurs along the dorsal and right surfaces of the epithecal portion of the test immediately apical of the girdle. Epithecal portion connected to the hypothecal portion of the test ventrally by a narrow strip of wall material rising from the left lateral ridge or from the floor of the longitudinal furrow near its midline.
Girdle is a subapical, neck-like structure, smaller in diameter than the epithecal portion of the test and poorly delimited from hypothecal portion on its left side. Dorsal and right lateral surfaces clearly defined and gently concave. Right surface merges with longitudinal furrow. No flagellar pores observed.
Hypothecal portion of test consists of large, broad, relatively flat right and left lateral surfaces and narrow dorsal and ventral surfaces. Shape of the hypothecal portion is: apical outline straight; dorsal outline slightly convex from girdle to antapical horn; antapical outline strongly concave between tips of horns; ventral outline straight to slightly convex and more or less parallel to dorsal surface from the antapical horn to approximately two-thirds the height of of the hypothecal portion, apical one-third of ventral outline straight and inclined apicoventrally. Right lateral surface longer antapically than left lateral surface. As a result of this length difference, each antapical horn consists of a longer right and a shorter left lobe. Tips of antapical horns narrowly rounded to pointed.
Archeopyle is epithecal and the adnate operculum joins the hypothecal portion of test ventrally. Epithecal portion of test and girdle are finely alveolate; lateral hypothecal surfaces are in part clear and in part finely to coarselv alveolate; dorsal and ventral surfaces are clear or irregularly alveolate with unevenly spaced, low, transverse ridges.
Affinities and discussion:
Stover, 1966, p.42-43: All specimens were seen in lateral view. Twenty-three of the 40 individuals are complete and most incomplete specimens are lacking only the epitheca (operculum).
Little variability was observed in the lateral outlines. Although the dorsal antapical horn tends to be slightly longer than the ventral antapical horn, and the right lateral surface is longer antapically than the left, these length differences do not seriously modify the subtriangular shape of the specimens.
The slender lateral ridges bordering the hypothecal portion of test vary from faint and low to prominent and well developed. They are usually pitted and commonly coincident with or very near and parallel to a line marking the extent of the lateral surface alveolation. The trace of the lateral ridges differs among specimens, especially in the antapical region. Typically, the right and left dorsal and right and left ventral ridges are parallel from below the girdle to about midway along the antapical horns. From there, the ridges become increasingly farther apart as they extend around the horns, then converge shortly after outlining the lobes of each antapical horn. After uniting, they continue as a single sagittal ridge in the antapical concavity. The condition described above and two variations are illustrated in text-figure 1.
The flattened left side of the epitheca is commonly triangular in outline and covered by a very thin wall. A tear or opening in the left epithecal wall, which may represent an apical pore, was observed on some specimens.
The test is thin, transparent or nearly so, and resistant to staining. Variation in surface sculpturing is believed due to preservation rather than to some inherent character of the species. Different areas on the same specimen may have fine alveolation, coarse alveolation, or be clear. In addition, comparable surface areas on different specimens rarely show identical sculpturing.
Comparison: Nannoceratopsis spiculata Stover differs from N. gracilis Alberti ( = N. defandrei Evitt) in: 1. Being longer and narrower; for specimens of N. gracilis with two clearly developed antapical horns, Evitt (1961) reports a mean length of 73 Ám and a mean width of 60 Ám. In comparison, the mean length and width for specimens of the new species are 96 and 55 Ám, respectively.
2. Having more elongate antapical horns and a deeper antapical cavity; none of the specimens of N. spiculata indicates even a slight tendency toward a marked reduction or loss of the ventral antapical horn as evidenced by specimens of N. gracilis.
3. Having less prominent lateral ridges and narrower dorsal and ventral surfaces.
4. Having a smaller epithecal portion of test which possesses a band-like thickening along its right side rather than a flap-like projection. The new species differs from N. pellucida Deflandre in having somewhat shorter and less divergent antapical horns and in having the right lateral surface of the hypothecal portion of test longer than the left lateral surface.
Holotype: Stover, 1966, pl.8, fig.1A-D
Locus typicus: Inferior Oolite Formation (middle part), Calvados, France
Stratum typicum: Bajocian-Bathonian
Original diagnosis: Stover, 1966, p.42
Non-tabulate fossil dinoflagellates witll a laterally flattened test, an acute apical end and two prominent antapical horns ol nearly equal size. Outline subtriangular; epithecal portion of test small; girdle well developed, especially along its right lateral and dorsal surfaces; hypotilecal portion much larger than epithecal portion of test. Right lateral surface of hypothecal portion of test longer antapically than left lateral surface. Dorsal and ventral surfaces narrow and usually bordered by low lateral ridges. Surface clear or finely to coarsely areolate. Mean length, 96 Ám; ean width, 55 Ám.
Original description: Stover, 1966, p.42
Test composed of a minute epithecal portion and a large hypothecal portion separated by a relatively high subapical girdle. In lateral view, the test is subtriangular in outline with an acute apex straight to convex sides and a deeply concave base. Narrow dorsal and ventral surfaces are bounded by lateral ridges. Specimens measure 81 to 102 Ám in length and 50 to 64 Ám in width across their widest part.
Epithecal portion of test is small, 4 to 8 Ám high and more or less conical, but with a truncated left lateral surface. A basal ridge or thickening occurs along the dorsal and right surfaces of the epithecal portion of the test immediately apical of the girdle. Epithecal portion connected to the hypothecal portion of the test ventrally by a narrow strip of wall material rising from the left lateral ridge or from the floor of the longitudinal furrow near its midline.
Girdle is a subapical, neck-like structure, smaller in diameter than the epithecal portion of the test and poorly delimited from hypothecal portion on its left side. Dorsal and right lateral surfaces clearly defined and gently concave. Right surface merges with longitudinal furrow. No flagellar pores observed.
Hypothecal portion of test consists of large, broad, relatively flat right and left lateral surfaces and narrow dorsal and ventral surfaces. Shape of the hypothecal portion is: apical outline straight; dorsal outline slightly convex from girdle to antapical horn; antapical outline strongly concave between tips of horns; ventral outline straight to slightly convex and more or less parallel to dorsal surface from the antapical horn to approximately two-thirds the height of of the hypothecal portion, apical one-third of ventral outline straight and inclined apicoventrally. Right lateral surface longer antapically than left lateral surface. As a result of this length difference, each antapical horn consists of a longer right and a shorter left lobe. Tips of antapical horns narrowly rounded to pointed.
Archeopyle is epithecal and the adnate operculum joins the hypothecal portion of test ventrally. Epithecal portion of test and girdle are finely alveolate; lateral hypothecal surfaces are in part clear and in part finely to coarselv alveolate; dorsal and ventral surfaces are clear or irregularly alveolate with unevenly spaced, low, transverse ridges.
Affinities and discussion:
Stover, 1966, p.42-43: All specimens were seen in lateral view. Twenty-three of the 40 individuals are complete and most incomplete specimens are lacking only the epitheca (operculum).
Little variability was observed in the lateral outlines. Although the dorsal antapical horn tends to be slightly longer than the ventral antapical horn, and the right lateral surface is longer antapically than the left, these length differences do not seriously modify the subtriangular shape of the specimens.
The slender lateral ridges bordering the hypothecal portion of test vary from faint and low to prominent and well developed. They are usually pitted and commonly coincident with or very near and parallel to a line marking the extent of the lateral surface alveolation. The trace of the lateral ridges differs among specimens, especially in the antapical region. Typically, the right and left dorsal and right and left ventral ridges are parallel from below the girdle to about midway along the antapical horns. From there, the ridges become increasingly farther apart as they extend around the horns, then converge shortly after outlining the lobes of each antapical horn. After uniting, they continue as a single sagittal ridge in the antapical concavity. The condition described above and two variations are illustrated in text-figure 1.
The flattened left side of the epitheca is commonly triangular in outline and covered by a very thin wall. A tear or opening in the left epithecal wall, which may represent an apical pore, was observed on some specimens.
The test is thin, transparent or nearly so, and resistant to staining. Variation in surface sculpturing is believed due to preservation rather than to some inherent character of the species. Different areas on the same specimen may have fine alveolation, coarse alveolation, or be clear. In addition, comparable surface areas on different specimens rarely show identical sculpturing.
Comparison: Nannoceratopsis spiculata Stover differs from N. gracilis Alberti ( = N. defandrei Evitt) in: 1. Being longer and narrower; for specimens of N. gracilis with two clearly developed antapical horns, Evitt (1961) reports a mean length of 73 Ám and a mean width of 60 Ám. In comparison, the mean length and width for specimens of the new species are 96 and 55 Ám, respectively.
2. Having more elongate antapical horns and a deeper antapical cavity; none of the specimens of N. spiculata indicates even a slight tendency toward a marked reduction or loss of the ventral antapical horn as evidenced by specimens of N. gracilis.
3. Having less prominent lateral ridges and narrower dorsal and ventral surfaces.
4. Having a smaller epithecal portion of test which possesses a band-like thickening along its right side rather than a flap-like projection. The new species differs from N. pellucida Deflandre in having somewhat shorter and less divergent antapical horns and in having the right lateral surface of the hypothecal portion of test longer than the left lateral surface.