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Eisenackia crassitabulata
Eisenackia crassitabulata Deflandre and Cookson, 1955; emend. McLean, 1973
Eisenackia crassitabulata was a nomen nudum in Deflandre and Cookson, 1954.
Holotype: pl.12, figs.1-2. Age: Late Miocene
Holotype: Deflandre and Cookson, 1955, pl.5, fig.2
Locus typicus: Pebble Point Formation, Victoria
Stratum typicum: Paleocene-Early Eocene
Original diagnosis: Deflandre and Cookson, 1955, p.258
Theca with a relatively thick wall, ellipsoidal, slightly compressed. Epitheca and hypotheca about equal. Transverse girdle level with the surface, slightly but clearly helicoidal. Longitudinal furrow level with the surface indicated on the epitheca by an elongated plate, and on the hypotheca by an inconspicuous and short ventral area. All the plates, including those constituting an equatorial belt corresponding to the girdle, are clearly outlined by a translucent, widely reticulate thickening. At the level of the belt, the girdle is marked not by a single depression but, on the contrary, by a medium elevation with a depression on both sides of it situated between it and the pre-equatorial and post-equatorial plates. All the spaces between the plates, and between the plates and the girdle, are ornamented with a linear thick-walled mesh of the same shape as the plates. In our material, treated as previously indicated and stained with safranin, the thick membrane is strongly coloured red, whilst the raised walls of the reticulum are either pink or uncoloured. Thus, in spite of reservations necessary on account of the age and treatment of the material, there seems to be a certain difference in composition between the 2 parts of the area, i.e. the thick basal membrane and superficial ornamentation.
The schematic tabulation has been obtained from the examination of some 20 specimens of which, however, only 2 have been complete. All the others have a large apical opening that corresponds with few exceptions to the position of the apical plates. These seem to have been interdependent and shed as a whole from the theca, but since all the specimens in an apical position have lost their apical plates, it has not been possible to determine their exact form and disposition. For this reason, therefore, the number 2-3" has been given in the generic description. It appears evident that, in this species, the opening formed by the detachment of the apical plates is related to some biological process either associated with the reproduction of the cell by divisions beneath the membrane, or with the exit of a cell after an encystment. In the latter eventuality there will not be a distinct cyst membrane, as is observed in many dinoflagellates, for example Deflandrea, which is present in the same deposit.
In addition to the apical plates just mentioned, the epitheca is composed of 6 pre-equatorial plates. One plate occupies the position of the upper longitudinal furrow. This plate can be compared with the more or less diamond-shaped 1st apical plate characteristic of the genus Peridinium. However, the general affinities of the genus Eisenackia do not approach the genus Peridinium, where an apical pore, absent in Eisenackia, is always found. Also it is more logical to consider this plate asrepresentingtheupper part of the longitudinal furrow. The pre-equatorial plates are unequal in size, plates 1" and 6" being clearly smaller than the others.
The hypotheca has been intact in all the specimens. It is composed of 6 post-equatorial plates, 1 antapical and 2 posterior intercalaries. The 1st post-equatorial plate 1""" is very small, and should be considered as 1 of the plates of the ventral area. This reduction of the 1st post-equatorial plate is not unusual in dinoflagellates and, generally speaking, our specimens show this plate more clearly than the others comprising the ventral area.
The antapical plate 1"""" is always pentagonal, and the 2 sides of the angle directed towards the ventral area are adjacent to the 2 small posterior intercalary plates 1p and 2p. The ventral area is relatively large and infavourable specimens it is possible to recognize 3 distinct plates and a possible 4th.
Dimensions: Relatively constant; length 72-78 Ám, breadth 55-67 Ám, depth 50-61 Ám. A single thicker and more globular specimen differs from all others, the length being 67 Ám and the breadth 58 Ám.
Affinities:
Deflandre and Cookson, 1955, p.258: The affinities of the genus Eisenackia are uncertain. In the flattened nature of the transverse furrow the new genus approaches the Podalampidae, especially the genus Blepharocysta. At first sight Eisenackia crassitabulata resembles B. striata Sch³tt, but this resemblance is quite superficial, for in the Podolampidae the shell either terminates in a horn-like process or there is an apical pore.
E. crasitabulata to some extent approaches the Protoceratidae, and more precisely the genus Protoceratium Bergh., in which there is no apical pore and the ornamentation is in the form of a thickwalled, wide-meshed reticulum, The tabulation of Protoceratium is 1-3", 0a, 6", 0-1p, 1-3"""". The variations indicated by various authors allow us to consider the tabulation of Eisenackia as coming within the limits of these variations. The fundamental difference between the 2 genera lies in the absence of a depressed furrow in Eisenackia. In the present state of our knowledge of the Dinoflagellata this character appears to be important, and to justify the creation of a new genus and perhaps a distinct family.
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Emended description: McLean 1973, p. 262-264
Cyst spheroidal to slightly ellipsoidal, lacking horns or processes; bi-layered; outer-wall layer occurs in shapes of plate-equivalents superimposed on inner layer, reflecting tabulation of 4", 0a, 6"", 6c, 1p, 1"""". Archeopyle apical (Type A) with shimple, free operculum; corresponds to four apical plate-equivalents plus an apical pore-closing platelet in their midst. Cingulum levorotatory; ends displaced vertically about one-half cingulum width and laterally three to four cingulum widths. Sulcal area (see Discussion) reflected at top and bottom by anterior and posterior sulcal plate-equivalants, respectively, and in between by two pairs of small plate-equivalents; of the anteriormost pair, the left-hand member is the larger and is designated as the 1 "", the other pair is between the 6"" and 1p plate-equivalants. Outer-wall layer 2-3µ thick; occurs in shapes of plate-equivalents superimposed on the innerwall layer; externally coarsely microreticulate Inner-wall layer 2-3µ thick; continuous, except at archeopyle; externally smooth to granulose to weakly microreticulate.
Dimensions: The dimensions of the specimen figured herein are L x W=50 x 45 Á Known length range=50 to 78Á; width range=45 to 67Á.
Remarks: McLean 1973, p. 262-264
The tabulation of Eisenackia crassitatiulata was onginally recorded as 2--3", 6" ?6, 6"", 2p, 1"" Deflandre and Cookson (1955) found no specimens with the operculum intact or oriented in such a way that the apex could be viewed directly, and recorded the apical tabulation as consisting of two or three apical plate-equivalents A specimen examined by the author has an operculum consisting of four apical plate-equivalents with a small apical pore-closing platelet in their midst (Fig 1); the operculum is simple and free The plate-equivalent designated 2p by Deflandre and Cookson corresponds in position to a typical Conyaulax-type posterior sulcal plate-equivalent and is so designated by the author. The postcingular tabulation is interpreted as consisting of six plate-equivalents; however, uncertainty exists concerning the interpretation of the anteriormost pair of small processes in the sulcal area. If both members of the pair are considered to be sulcal plate- equivalents, five postcingulars are indicated If, however, the left-hand, larger member of the pair is considered a postcingular plate-equivalent, six postcingulars are indicated. Because the thecae of many modern dinoflagellate species display reduced 1"" plates, the latter course was followed in interpreting the fossil.
Comparison with similar species. The combinayion of tabulation type apical archeopyle type and the nature of the outer-wall layer occurring in the shapes of the plale-equivalents differentiates Eisenackia crassitabulata from other similarly shaped species.
Occurrence: The specimens investigated for this paper are from a sample collected at the locality discussed under Materials and methods. The sample was taken about 25 feet from the top of the section. Eisenackia crassitabulata constitutes less than 1 per cent of the phytoplankton content of the sample.
Previously reported occurrence: Paleocene to Lower Eocene of Australia (Deflandre & Cookson 1954, 1955); Upper Paleocene of Germany (Alberti 1961); Upper Paleocene til lowermost Eocene of Russia (Alberti 1961); Middle Paleocene of Australia (Cookson & Eisenack 1965); Cenomanian to Santonian of England (Clarke and Verdier 1967); Eocene of Chile (Cookson and Cranwell 1967); Danian of California (Drugg 1967).
Eisenackia crassitabulata was a nomen nudum in Deflandre and Cookson, 1954.
Holotype: pl.12, figs.1-2. Age: Late Miocene
Holotype: Deflandre and Cookson, 1955, pl.5, fig.2
Locus typicus: Pebble Point Formation, Victoria
Stratum typicum: Paleocene-Early Eocene
Original diagnosis: Deflandre and Cookson, 1955, p.258
Theca with a relatively thick wall, ellipsoidal, slightly compressed. Epitheca and hypotheca about equal. Transverse girdle level with the surface, slightly but clearly helicoidal. Longitudinal furrow level with the surface indicated on the epitheca by an elongated plate, and on the hypotheca by an inconspicuous and short ventral area. All the plates, including those constituting an equatorial belt corresponding to the girdle, are clearly outlined by a translucent, widely reticulate thickening. At the level of the belt, the girdle is marked not by a single depression but, on the contrary, by a medium elevation with a depression on both sides of it situated between it and the pre-equatorial and post-equatorial plates. All the spaces between the plates, and between the plates and the girdle, are ornamented with a linear thick-walled mesh of the same shape as the plates. In our material, treated as previously indicated and stained with safranin, the thick membrane is strongly coloured red, whilst the raised walls of the reticulum are either pink or uncoloured. Thus, in spite of reservations necessary on account of the age and treatment of the material, there seems to be a certain difference in composition between the 2 parts of the area, i.e. the thick basal membrane and superficial ornamentation.
The schematic tabulation has been obtained from the examination of some 20 specimens of which, however, only 2 have been complete. All the others have a large apical opening that corresponds with few exceptions to the position of the apical plates. These seem to have been interdependent and shed as a whole from the theca, but since all the specimens in an apical position have lost their apical plates, it has not been possible to determine their exact form and disposition. For this reason, therefore, the number 2-3" has been given in the generic description. It appears evident that, in this species, the opening formed by the detachment of the apical plates is related to some biological process either associated with the reproduction of the cell by divisions beneath the membrane, or with the exit of a cell after an encystment. In the latter eventuality there will not be a distinct cyst membrane, as is observed in many dinoflagellates, for example Deflandrea, which is present in the same deposit.
In addition to the apical plates just mentioned, the epitheca is composed of 6 pre-equatorial plates. One plate occupies the position of the upper longitudinal furrow. This plate can be compared with the more or less diamond-shaped 1st apical plate characteristic of the genus Peridinium. However, the general affinities of the genus Eisenackia do not approach the genus Peridinium, where an apical pore, absent in Eisenackia, is always found. Also it is more logical to consider this plate asrepresentingtheupper part of the longitudinal furrow. The pre-equatorial plates are unequal in size, plates 1" and 6" being clearly smaller than the others.
The hypotheca has been intact in all the specimens. It is composed of 6 post-equatorial plates, 1 antapical and 2 posterior intercalaries. The 1st post-equatorial plate 1""" is very small, and should be considered as 1 of the plates of the ventral area. This reduction of the 1st post-equatorial plate is not unusual in dinoflagellates and, generally speaking, our specimens show this plate more clearly than the others comprising the ventral area.
The antapical plate 1"""" is always pentagonal, and the 2 sides of the angle directed towards the ventral area are adjacent to the 2 small posterior intercalary plates 1p and 2p. The ventral area is relatively large and infavourable specimens it is possible to recognize 3 distinct plates and a possible 4th.
Dimensions: Relatively constant; length 72-78 Ám, breadth 55-67 Ám, depth 50-61 Ám. A single thicker and more globular specimen differs from all others, the length being 67 Ám and the breadth 58 Ám.
Affinities:
Deflandre and Cookson, 1955, p.258: The affinities of the genus Eisenackia are uncertain. In the flattened nature of the transverse furrow the new genus approaches the Podalampidae, especially the genus Blepharocysta. At first sight Eisenackia crassitabulata resembles B. striata Sch³tt, but this resemblance is quite superficial, for in the Podolampidae the shell either terminates in a horn-like process or there is an apical pore.
E. crasitabulata to some extent approaches the Protoceratidae, and more precisely the genus Protoceratium Bergh., in which there is no apical pore and the ornamentation is in the form of a thickwalled, wide-meshed reticulum, The tabulation of Protoceratium is 1-3", 0a, 6", 0-1p, 1-3"""". The variations indicated by various authors allow us to consider the tabulation of Eisenackia as coming within the limits of these variations. The fundamental difference between the 2 genera lies in the absence of a depressed furrow in Eisenackia. In the present state of our knowledge of the Dinoflagellata this character appears to be important, and to justify the creation of a new genus and perhaps a distinct family.
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Emended description: McLean 1973, p. 262-264
Cyst spheroidal to slightly ellipsoidal, lacking horns or processes; bi-layered; outer-wall layer occurs in shapes of plate-equivalents superimposed on inner layer, reflecting tabulation of 4", 0a, 6"", 6c, 1p, 1"""". Archeopyle apical (Type A) with shimple, free operculum; corresponds to four apical plate-equivalents plus an apical pore-closing platelet in their midst. Cingulum levorotatory; ends displaced vertically about one-half cingulum width and laterally three to four cingulum widths. Sulcal area (see Discussion) reflected at top and bottom by anterior and posterior sulcal plate-equivalants, respectively, and in between by two pairs of small plate-equivalents; of the anteriormost pair, the left-hand member is the larger and is designated as the 1 "", the other pair is between the 6"" and 1p plate-equivalants. Outer-wall layer 2-3µ thick; occurs in shapes of plate-equivalents superimposed on the innerwall layer; externally coarsely microreticulate Inner-wall layer 2-3µ thick; continuous, except at archeopyle; externally smooth to granulose to weakly microreticulate.
Dimensions: The dimensions of the specimen figured herein are L x W=50 x 45 Á Known length range=50 to 78Á; width range=45 to 67Á.
Remarks: McLean 1973, p. 262-264
The tabulation of Eisenackia crassitatiulata was onginally recorded as 2--3", 6" ?6, 6"", 2p, 1"" Deflandre and Cookson (1955) found no specimens with the operculum intact or oriented in such a way that the apex could be viewed directly, and recorded the apical tabulation as consisting of two or three apical plate-equivalents A specimen examined by the author has an operculum consisting of four apical plate-equivalents with a small apical pore-closing platelet in their midst (Fig 1); the operculum is simple and free The plate-equivalent designated 2p by Deflandre and Cookson corresponds in position to a typical Conyaulax-type posterior sulcal plate-equivalent and is so designated by the author. The postcingular tabulation is interpreted as consisting of six plate-equivalents; however, uncertainty exists concerning the interpretation of the anteriormost pair of small processes in the sulcal area. If both members of the pair are considered to be sulcal plate- equivalents, five postcingulars are indicated If, however, the left-hand, larger member of the pair is considered a postcingular plate-equivalent, six postcingulars are indicated. Because the thecae of many modern dinoflagellate species display reduced 1"" plates, the latter course was followed in interpreting the fossil.
Comparison with similar species. The combinayion of tabulation type apical archeopyle type and the nature of the outer-wall layer occurring in the shapes of the plale-equivalents differentiates Eisenackia crassitabulata from other similarly shaped species.
Occurrence: The specimens investigated for this paper are from a sample collected at the locality discussed under Materials and methods. The sample was taken about 25 feet from the top of the section. Eisenackia crassitabulata constitutes less than 1 per cent of the phytoplankton content of the sample.
Previously reported occurrence: Paleocene to Lower Eocene of Australia (Deflandre & Cookson 1954, 1955); Upper Paleocene of Germany (Alberti 1961); Upper Paleocene til lowermost Eocene of Russia (Alberti 1961); Middle Paleocene of Australia (Cookson & Eisenack 1965); Cenomanian to Santonian of England (Clarke and Verdier 1967); Eocene of Chile (Cookson and Cranwell 1967); Danian of California (Drugg 1967).