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Volkheimeridium irmoechinatum
From Fensome et al., 2019:
Volkheimeridium irmoechinatum (Heisecke, 1970, p.230, pl.1, fig.3; pl.2, figs.2–3) Quattrocchio and Sarjeant, 2003, p138.
NOW Spinidinium? Originally Deflandrea, subsequently Gonyaulacysta, thirdly (and now) Spinidinium?, fourthly ?Volkheimeridium. Questionable assignment: Quattrocchio and Sarjeant (2003, p.138). Sluijs et al. (2009,p.47) questionably retained this species in Spinidinium.
Holotype: Heisecke, 1970, pl.1, fig.3; pl.2, figs.2–3.
Age: early Paleocene.
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Original description (Heisecke, 1970) Not yet translated from Spanish.
DIAGNOSIS. Cavate cyst with an irregular bipyramidal contour. The wall is covered with spines, forming an apical and an antiapical horn. The spines are preferably arranged in a line, often joined by delicate partitions, delimiting a circular girdle and a very characteristic sulcal area. No type of opening is observed.
HOLOTYPE. Slide 429( 4), coordinates 54.8/105.
DIMENSIONS. Total length 68 µm, length (without horns) 38 µm, width 43.5 µm, length of spines 1-3.5 µm, height of septa 2-9 µm, angle width 3.5 µm, apical horn 12.5 µm, antiapical horn 17 µm,
DESCRIPTION. Caved cyst with irregular bipyramidal contour. The wall is composed of two layers, the outer one forming a pyramidal apical horn culminating in two spines and an antiapical horn densely covered with spines. The surface is covered by spines that are preferably arranged in a line and often joined by delicate septa, thus delimiting the plates. In some cases this limit is indicated by a septum up to 9 µm. high, ending in small spines. The circular cingulum is very characteristic, as it is depressed, free of spines and almost continuously bordered by spiny ridges or septa. The sulcal area is also bordered by spiny ridges or septa and is restricted to the hypotract and the cingulum; in the epitract it narrows, forming a simple border between the plates. The tabulation. The reflected area is 5', 6", 6c(-7c), 6"', ls(2s), lp(?), l"''. Plate 7c is smaller than the other cingular plates as it coincides with the width of the sulcal area, and is therefore considered to be either the cingular plate or the sulcal plate. The plate doubtfully considered lp has an unusual position, as it is located between 2"' and 3"'. The limit between plates 3" and 4" is not clearly defined, but only hinted at. No opening of any kind has been observed.
OBSERVATIONS. The specimens in preparation 429 (4), coordinates 4 5 ,3 / 95; 53,2/ 107,8; 53,9/105,6 are smaller than the one previously described (total length 44-48 p., width 23-30 p.) and lack an antiapical horn, presenting only a prominence that culminates in a spine. However, they have a very similar appearance to the one previously described, since they have a well-marked angle and a large number of spines joined by partitions, delimiting areas, but this characteristic is unclear so that the tabulation could not be determined. These specimens, due to the absence of antiapical horns, presenting the antiapical prominence that culminates in a spine and due to their dimensions, also resemble Spinidinium rallum sp. nov. from which they differ in having a well-defined angle and possibly a greater number of spines. From these similarities it can be deduced that the presence of the two genera, Spinidinium and Deflandrea, is, in this case, arbitrary since in three forms with few differences between them, one gradually passes from one genus to the other.
COMPARISONS. The new species resembles Palaeoperidinium murciforme Conrad, 1941 in its general appearance, the presence of a depressed angle and the possession of crests that culminate in spines.
However, it differs from this species in the type of spines that are much stronger in P. murciforme, in the presence of two antiapical horns, one very reduced and the tabulation that is not determinable.
It differs from the specimen of Deflandrea cf. macmurdoensis described in this work because it has two more or less well-developed antiapical horns and a precingular archeopyle and because of the absence of tabulation, in addition to a different general appearance and form. Therefore, despite being a single specimen and until more data are obtained, it is provisionally considered a new species because the available specimen presents very clear and defined characteristics.
HORIZON. Sample MH2.
Derivation of name:. From the Greek serie, chain, and from the Latin echinatul' derived from the Greek hedgehog, referring to the alignment of the spines at the limits between the plates.
Volkheimeridium irmoechinatum (Heisecke, 1970, p.230, pl.1, fig.3; pl.2, figs.2–3) Quattrocchio and Sarjeant, 2003, p138.
NOW Spinidinium? Originally Deflandrea, subsequently Gonyaulacysta, thirdly (and now) Spinidinium?, fourthly ?Volkheimeridium. Questionable assignment: Quattrocchio and Sarjeant (2003, p.138). Sluijs et al. (2009,p.47) questionably retained this species in Spinidinium.
Holotype: Heisecke, 1970, pl.1, fig.3; pl.2, figs.2–3.
Age: early Paleocene.
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Original description (Heisecke, 1970) Not yet translated from Spanish.
DIAGNOSIS. Cavate cyst with an irregular bipyramidal contour. The wall is covered with spines, forming an apical and an antiapical horn. The spines are preferably arranged in a line, often joined by delicate partitions, delimiting a circular girdle and a very characteristic sulcal area. No type of opening is observed.
HOLOTYPE. Slide 429( 4), coordinates 54.8/105.
DIMENSIONS. Total length 68 µm, length (without horns) 38 µm, width 43.5 µm, length of spines 1-3.5 µm, height of septa 2-9 µm, angle width 3.5 µm, apical horn 12.5 µm, antiapical horn 17 µm,
DESCRIPTION. Caved cyst with irregular bipyramidal contour. The wall is composed of two layers, the outer one forming a pyramidal apical horn culminating in two spines and an antiapical horn densely covered with spines. The surface is covered by spines that are preferably arranged in a line and often joined by delicate septa, thus delimiting the plates. In some cases this limit is indicated by a septum up to 9 µm. high, ending in small spines. The circular cingulum is very characteristic, as it is depressed, free of spines and almost continuously bordered by spiny ridges or septa. The sulcal area is also bordered by spiny ridges or septa and is restricted to the hypotract and the cingulum; in the epitract it narrows, forming a simple border between the plates. The tabulation. The reflected area is 5', 6", 6c(-7c), 6"', ls(2s), lp(?), l"''. Plate 7c is smaller than the other cingular plates as it coincides with the width of the sulcal area, and is therefore considered to be either the cingular plate or the sulcal plate. The plate doubtfully considered lp has an unusual position, as it is located between 2"' and 3"'. The limit between plates 3" and 4" is not clearly defined, but only hinted at. No opening of any kind has been observed.
OBSERVATIONS. The specimens in preparation 429 (4), coordinates 4 5 ,3 / 95; 53,2/ 107,8; 53,9/105,6 are smaller than the one previously described (total length 44-48 p., width 23-30 p.) and lack an antiapical horn, presenting only a prominence that culminates in a spine. However, they have a very similar appearance to the one previously described, since they have a well-marked angle and a large number of spines joined by partitions, delimiting areas, but this characteristic is unclear so that the tabulation could not be determined. These specimens, due to the absence of antiapical horns, presenting the antiapical prominence that culminates in a spine and due to their dimensions, also resemble Spinidinium rallum sp. nov. from which they differ in having a well-defined angle and possibly a greater number of spines. From these similarities it can be deduced that the presence of the two genera, Spinidinium and Deflandrea, is, in this case, arbitrary since in three forms with few differences between them, one gradually passes from one genus to the other.
COMPARISONS. The new species resembles Palaeoperidinium murciforme Conrad, 1941 in its general appearance, the presence of a depressed angle and the possession of crests that culminate in spines.
However, it differs from this species in the type of spines that are much stronger in P. murciforme, in the presence of two antiapical horns, one very reduced and the tabulation that is not determinable.
It differs from the specimen of Deflandrea cf. macmurdoensis described in this work because it has two more or less well-developed antiapical horns and a precingular archeopyle and because of the absence of tabulation, in addition to a different general appearance and form. Therefore, despite being a single specimen and until more data are obtained, it is provisionally considered a new species because the available specimen presents very clear and defined characteristics.
HORIZON. Sample MH2.
Derivation of name:. From the Greek serie, chain, and from the Latin echinatul' derived from the Greek hedgehog, referring to the alignment of the spines at the limits between the plates.