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Spinidinium irmoechinatum
From Fensome et al., 2019:
Spinidinium ?irmoechinatum (Heisecke, 1970, p.230, pl.1, fig.3; pl.2, figs.2–3) Stover and Evitt, 1978, p.125. Holotype: Heisecke, 1970, pl.1, fig.3; pl.2, figs.2–3. Originally Deflandrea, subsequently Gonyaulacysta, thirdly (and now) Spinidinium?, fourthly Volkheimeridium. Questionable assignment: Stover and Evitt (1978, p.125). Sluijs et al. (2009,p.47) questionably retained this species in Spinidinium. Age: Early Paleocene.
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Original description (Heisecke, 1970) Translation PKB 2025:
DIAGNOSIS. Excavated cyst with an irregular bipyramidal outline. The wall is covered with spines, forming an apical and an antiapical horn. The spines are preferentially arranged in a line, often joined by delicate septa, delimiting a characteristic circular cingulum and sulcal area. No aperture is observed.
HOLOTYPE. Preparation 429(4), coordinates 54.8/105.
DIMENSIONS. Total length 68 µm, length (without horns) 38 µm, width 43.5 µm, spine length 1-3.5 µm, septum height 2-9 µm, cingulum thickness 3.5 µm, apical horn 12.5 µm, antiapical horn 17 µm.
DESCRIPTION. Excavated cyst with an irregular bipyramidal outline. The wall is composed of two layers: the outer layer forms a pyramidal apical horn that terminates in two spines and an antiapical horn densely covered with spines. The surface is covered with spines that are preferentially aligned and often joined by delicate septa, thus delimiting the plates. In some cases, this boundary is indicated by a septum up to 9 µm high that terminates in small spines. The circular cingulum is bi-characteristic, as it is depressed, free of spines, and almost continuously delimited by spiny ridges or septa. The sulcal area is also delimited by spiny ridges or septa and is restricted to the hypotract and the cingulum; in the epitract, it narrows, forming a simple boundary between plates. Tabulation. The reflected plate is 5', 6", 6c(-7c), 6"', ls(2s), lp(?), 1"''. Plate 7c is smaller than the other cingulate plates because it coincides with the width of the sulcal area, so it is considered interchangeably as a cingulate plate or sulcal plate. The plate considered doubtful, lp, has an unusual position, as it is located between 2"' and 3"'. The boundary between plates 3" and 4" is not clearly defined, but only suggested. No type of opening has been observed.
OBSERVATIONS. The specimens in preparation 429 (4), coordinates 45.3/95; 53.2/107.8; 53.9/105.6, are smaller than the one previously described (total length 44-48 pp., width 23-30 pp.) 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 present a well-marked angle and a large number of spines joined by septa, delimiting areas, but this characteristic is unclear so that the tabulation could not be determined. These specimens, due to the absence of antiapical horns, the presence of the antiapical prominence that culminates in a spine, and their dimensions, also resemble Spinidinium rallum sp. nov. They differ in having a well-defined angle and possibly a greater number of spines. From these similarities, it follows that the presence of the two genera, Spinidinium and Deflandrea, is arbitrary in this case, since in three forms with few differences between them, one gradually transitions 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 ridges that terminate in spines.
However, it differs from that species in the type of spines, which are much stronger in *P. murciforme*, in the presence of two antiapical horns, one of which is very reduced, and in the tabulation, which is indeterminable.
It differs from the *Deflandrea cf. macmurdoensis* specimen described in this work in that the latter possesses two more or less well-developed antiapical horns and a precingulate archeopyle, and in the absence of tabulation, in addition to a different general appearance and shape. Therefore, despite being a single specimen, and until further data are obtained, it is provisionally considered a new species because the available specimen presents very clear and defined characteristics.
HORIZON. Specimen MH2. DERIVATIO NOMINIS. From the Greek serie, concadena, and from the Latin echinatul, derived from the Greek erizo, referring to the alignment of spines at the boundaries between plates.
Spinidinium ?irmoechinatum (Heisecke, 1970, p.230, pl.1, fig.3; pl.2, figs.2–3) Stover and Evitt, 1978, p.125. Holotype: Heisecke, 1970, pl.1, fig.3; pl.2, figs.2–3. Originally Deflandrea, subsequently Gonyaulacysta, thirdly (and now) Spinidinium?, fourthly Volkheimeridium. Questionable assignment: Stover and Evitt (1978, p.125). Sluijs et al. (2009,p.47) questionably retained this species in Spinidinium. Age: Early Paleocene.
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Original description (Heisecke, 1970) Translation PKB 2025:
DIAGNOSIS. Excavated cyst with an irregular bipyramidal outline. The wall is covered with spines, forming an apical and an antiapical horn. The spines are preferentially arranged in a line, often joined by delicate septa, delimiting a characteristic circular cingulum and sulcal area. No aperture is observed.
HOLOTYPE. Preparation 429(4), coordinates 54.8/105.
DIMENSIONS. Total length 68 µm, length (without horns) 38 µm, width 43.5 µm, spine length 1-3.5 µm, septum height 2-9 µm, cingulum thickness 3.5 µm, apical horn 12.5 µm, antiapical horn 17 µm.
DESCRIPTION. Excavated cyst with an irregular bipyramidal outline. The wall is composed of two layers: the outer layer forms a pyramidal apical horn that terminates in two spines and an antiapical horn densely covered with spines. The surface is covered with spines that are preferentially aligned and often joined by delicate septa, thus delimiting the plates. In some cases, this boundary is indicated by a septum up to 9 µm high that terminates in small spines. The circular cingulum is bi-characteristic, as it is depressed, free of spines, and almost continuously delimited by spiny ridges or septa. The sulcal area is also delimited by spiny ridges or septa and is restricted to the hypotract and the cingulum; in the epitract, it narrows, forming a simple boundary between plates. Tabulation. The reflected plate is 5', 6", 6c(-7c), 6"', ls(2s), lp(?), 1"''. Plate 7c is smaller than the other cingulate plates because it coincides with the width of the sulcal area, so it is considered interchangeably as a cingulate plate or sulcal plate. The plate considered doubtful, lp, has an unusual position, as it is located between 2"' and 3"'. The boundary between plates 3" and 4" is not clearly defined, but only suggested. No type of opening has been observed.
OBSERVATIONS. The specimens in preparation 429 (4), coordinates 45.3/95; 53.2/107.8; 53.9/105.6, are smaller than the one previously described (total length 44-48 pp., width 23-30 pp.) 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 present a well-marked angle and a large number of spines joined by septa, delimiting areas, but this characteristic is unclear so that the tabulation could not be determined. These specimens, due to the absence of antiapical horns, the presence of the antiapical prominence that culminates in a spine, and their dimensions, also resemble Spinidinium rallum sp. nov. They differ in having a well-defined angle and possibly a greater number of spines. From these similarities, it follows that the presence of the two genera, Spinidinium and Deflandrea, is arbitrary in this case, since in three forms with few differences between them, one gradually transitions 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 ridges that terminate in spines.
However, it differs from that species in the type of spines, which are much stronger in *P. murciforme*, in the presence of two antiapical horns, one of which is very reduced, and in the tabulation, which is indeterminable.
It differs from the *Deflandrea cf. macmurdoensis* specimen described in this work in that the latter possesses two more or less well-developed antiapical horns and a precingulate archeopyle, and in the absence of tabulation, in addition to a different general appearance and shape. Therefore, despite being a single specimen, and until further data are obtained, it is provisionally considered a new species because the available specimen presents very clear and defined characteristics.
HORIZON. Specimen MH2. DERIVATIO NOMINIS. From the Greek serie, concadena, and from the Latin echinatul, derived from the Greek erizo, referring to the alignment of spines at the boundaries between plates.