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Eodinia pachytheca
From Fensome et al., 2019:
Eodinia pachytheca Eisenack, 1936, p.73–75, text-figs.1–6. Emendation: Gocht, 1975a, p.27. Holotype: Eisenack, 1936,
text-fig.1; Gocht, 1975a, figs.21a–b. Age: Callovian.
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Original description (Eisenack, 1936) Translation PKB 2025:
The carapace of this species consists of two parts, the epicyst and the hypocyst. The former is generally flat, hemispherical with a short, superimposed horn; the latter is rounded, truncated, and taller than the epicyst. The interior is more ovoid and extends only slightly, or not at all, into the horn. In completely undamaged carapace, a transverse furrow or suture is difficult to detect, but carapace specimens are often found that have burst at the annular suture, leaving the two halves, only loosely connected, more or less wide apart. In others, even a fine trace indicates this dividing line. Often, the individual halves are also present. The annular suture is completely circular; in posterior section, it sometimes appears as a fine V-shaped notch in the carapace wall. It is, in fact, only a "seam," not a girdle consisting of separate plates. It encircles the carapace at its greatest circumference. The longitudinal furrow is even more difficult to detect. As such, one must consider an indentation that begins shallowly at the transverse groove and extends on the hypocyst to about halfway up the antapex, thus not reaching it. Its deepest point is approximately in its center. The thickness of the carapace prevents it from being visible in a lateral view of the hypocyst. In the polar view of the hypocyst, it appears as an indentation in the otherwise circular cross-section. It does not extend to the epicyst. The shell is relatively thick and completely unclad. It appears to be perforated by numerous pores, which may be dot-like or streaky. Whether the apical horn is pierced by a fine pore remains undecided, although it sometimes appears so. The color of the shell is yellowish to light brown. If the shell is ignited, it first darkens (charring of organic substances) and then whitens; it does not burn. Concentrated sulfuric acid only darkens it without destroying it. It is therefore composed of silica. Treated with zinc chloride-iodine, it becomes yellowish-brown, even if it was lighter in color. This can also be attributed to organic substances, but which rules out the presence of cellulose, at least in its current state, as a component of the shell substance. This is consistent with the negative behavior between crossed Nikols in polarized light. The size varies between approximately 100-120 µ; The transverse diameter is between approximately 84-100 µm. These forms are usually somewhat longer than they are wide, but some are also found with a nearly equal longitudinal and transverse diameter. This species was quite common in the above-mentioned drift, so that approximately 100 specimens could be prepared. The structure of the carapace, consisting of two completely unclad shells that meet in a roughly circular seam, and especially the absence of a girdle carapace, places our form in the anterior division of the Adiniferae Linden., specifically in the class Thecatales Lindem., although its other habitus differs considerably from that of the recent dinoflagellates included in this group. The possession of pores, similar to those found in the carapace of the genus Exuviaella, could also support the above-mentioned opinion, especially since the polar view of the hypovalva presents a similar appearance to that of Exuviaella compressa Ostenfled. However, I would like to point out that this comparison of a Jurassic form with recent species and the attempt to classify this, for the time being, quite isolated fossil species into the system of present-day dinoflagellates must have something unsatisfactory about it. I would also like to draw attention to a certain similarity between our species and Berghiella perplexa, of which Koffoid & Mitchener have so far only given a description and a small illustration. This form, belonging to the class Kolkwitziellales Lindem, also has an unclad shell and, based on the description, appears to be quite similar to our species. However, the presence of a pronounced girdle furrow constitutes a significant systematic difference. In any case, it can be said that Eodinia is a very primitive form. The discovery of a second Jurassic dinoflagellate with a siliceous shell, especially in a rock that did not show the slightest trace of silicification, leads me to believe that, both here and in Lithodinia jurassica, this shell formation is indeed primary. This could be seen as support for the occasionally expressed view of the relationship between dinoflagellates and diatoms.
Eodinia pachytheca Eisenack, 1936, p.73–75, text-figs.1–6. Emendation: Gocht, 1975a, p.27. Holotype: Eisenack, 1936,
text-fig.1; Gocht, 1975a, figs.21a–b. Age: Callovian.
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Original description (Eisenack, 1936) Translation PKB 2025:
The carapace of this species consists of two parts, the epicyst and the hypocyst. The former is generally flat, hemispherical with a short, superimposed horn; the latter is rounded, truncated, and taller than the epicyst. The interior is more ovoid and extends only slightly, or not at all, into the horn. In completely undamaged carapace, a transverse furrow or suture is difficult to detect, but carapace specimens are often found that have burst at the annular suture, leaving the two halves, only loosely connected, more or less wide apart. In others, even a fine trace indicates this dividing line. Often, the individual halves are also present. The annular suture is completely circular; in posterior section, it sometimes appears as a fine V-shaped notch in the carapace wall. It is, in fact, only a "seam," not a girdle consisting of separate plates. It encircles the carapace at its greatest circumference. The longitudinal furrow is even more difficult to detect. As such, one must consider an indentation that begins shallowly at the transverse groove and extends on the hypocyst to about halfway up the antapex, thus not reaching it. Its deepest point is approximately in its center. The thickness of the carapace prevents it from being visible in a lateral view of the hypocyst. In the polar view of the hypocyst, it appears as an indentation in the otherwise circular cross-section. It does not extend to the epicyst. The shell is relatively thick and completely unclad. It appears to be perforated by numerous pores, which may be dot-like or streaky. Whether the apical horn is pierced by a fine pore remains undecided, although it sometimes appears so. The color of the shell is yellowish to light brown. If the shell is ignited, it first darkens (charring of organic substances) and then whitens; it does not burn. Concentrated sulfuric acid only darkens it without destroying it. It is therefore composed of silica. Treated with zinc chloride-iodine, it becomes yellowish-brown, even if it was lighter in color. This can also be attributed to organic substances, but which rules out the presence of cellulose, at least in its current state, as a component of the shell substance. This is consistent with the negative behavior between crossed Nikols in polarized light. The size varies between approximately 100-120 µ; The transverse diameter is between approximately 84-100 µm. These forms are usually somewhat longer than they are wide, but some are also found with a nearly equal longitudinal and transverse diameter. This species was quite common in the above-mentioned drift, so that approximately 100 specimens could be prepared. The structure of the carapace, consisting of two completely unclad shells that meet in a roughly circular seam, and especially the absence of a girdle carapace, places our form in the anterior division of the Adiniferae Linden., specifically in the class Thecatales Lindem., although its other habitus differs considerably from that of the recent dinoflagellates included in this group. The possession of pores, similar to those found in the carapace of the genus Exuviaella, could also support the above-mentioned opinion, especially since the polar view of the hypovalva presents a similar appearance to that of Exuviaella compressa Ostenfled. However, I would like to point out that this comparison of a Jurassic form with recent species and the attempt to classify this, for the time being, quite isolated fossil species into the system of present-day dinoflagellates must have something unsatisfactory about it. I would also like to draw attention to a certain similarity between our species and Berghiella perplexa, of which Koffoid & Mitchener have so far only given a description and a small illustration. This form, belonging to the class Kolkwitziellales Lindem, also has an unclad shell and, based on the description, appears to be quite similar to our species. However, the presence of a pronounced girdle furrow constitutes a significant systematic difference. In any case, it can be said that Eodinia is a very primitive form. The discovery of a second Jurassic dinoflagellate with a siliceous shell, especially in a rock that did not show the slightest trace of silicification, leads me to believe that, both here and in Lithodinia jurassica, this shell formation is indeed primary. This could be seen as support for the occasionally expressed view of the relationship between dinoflagellates and diatoms.