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Spinidinium stellatum
Spinidinium stellatum Soncini, 1992
Holotype: Soncini, 1992, pl.3, figs.1-3
Locus typicus: Abdoun, Morocco
Stratum typicum: Thanetian-Ypresian
Original diagnosis: Soncini, 1992, p.335
Rounded polygonal, compressed dorsoventrally, proximochorate two-layered cyst, circumcavate (to bicavate). Short apical horn truncated, left antapical horn variable in length, pointed, right antapical reduced or absent. Broad and laterally prominent paracingulum. Numerous projections on cyst surface, variable in length and shape complexity. Tapering proximally, with pericoele often protruding into their base; solid stem short to long, narrow to broad; distal part simple, bifurcate, trifurcate or more; at any scale, every distal extremity expanding and aculeate. Paratabulation evident (except in paracingular and parasulcal areas), peridinioid ortho- (ventral side) hexa type (dorsal side). Projections in parasutural position on ventral side, in penitabular position on dorsal side, partially missing on 2a intercalary paraplate (border-side with 4") and on 3""" (borderside with paracingulum), absent in the paracingulum and the sulcal areas. Strong antapical dissymmetry, 2"""" large and almost centered, 1"""" reduced to the left antapical horn. Peri- and endo-archeopyle type la, eurydeltaform. Perioperculum commonly adnate, endoperculum adnate, rarely discernible.
Dimensions: holotype length: 95.5 µm, width: 77 µm; range length: 67-116.5 µm, width: 60.5-112 µm; processes length: 2-9.5 µm (homogeneous on each specimen); 120 specimens measured.
Original description: Soncini, 1992, p.335-336
Spinidinium stellatum cysts are two layered, the endophragm is thin and smooth, spheroidal, variably appressed to the periphragm (circumcavate to bicavate). The periphragm is generally smooth or shagrinate, but sometimes foveolate (Plate lll, 5, 6). Straight, long and simple projections are particularly well developed on the extremities of apical and antapical horn (Plate lll, 4). Paracingulum borders are also prominent, underlined by more complex projections: simple, bifid or trifid, they can be linked together proximally in a discontinuous ridge. Although they are homogeneous on a single specimen, projections show a great diversity in shape and length (Fig.7); it is then hard to call them "spines" or "processes". With short or long, narrow or broad solid stem, straight or branched, bifid, trifid, they are all distally expanded and aculeate, but the rows of minute acuminate spines are hardly discernible (Plate III, 13, 14). Anyway, the first striking feature all projections have in common is their roughly star-shaped tip (hence the species name: stellatum).
Projections are scarce on paraplates surface, but numerous in parasutural position on ventral side (Plate III, 3), and in penitabular position on dorsal side (Plate III, 1, 10, 11) (rare specimens with just few "diminutive processes" underlying paratabulation). Lack of projection on posterior margin of intercalary paraplate 2a (contact 2a/u"), and on the anterior margin of postcingular paraplate 3""" (contact 3"""/paracing.) are also diagnostic features (Fig.8). Paratabulation peridinioid, with ventral ortho-type. Dorsally, la and 3a intercalaries seem to be smaller than the six-sided 2a (hexa-type). The archeopyle (type la) is eurydeltaform (Plate III, 1), the operculum (2a) is generally adnate (Plate III, 10). The endoperculum is also adnate and eurydeltaform, sometimes discernible inside the cyst (Plate III, 4).
Affinities:
Soncini, 1992, p.336: Although it belongs clearly to the genus Spinidinium, S. stellatum differs greatly from other Spinidinium species: with the penitabular and parasutural distribution of the projections (commonly covering the surface of the cyst except on pandasutural areas on other paratabulated Spinidinium species);
- with the complexity of these projections: short to long spines (like most Spinidinium) or diminutive processes typically expanded and aculeate (very distinctive character). Some features in S. stellatum suggest morphological affinities with the Wetzeliellaceae: processes distribution could compare with some Wilsonidium Lentin and Williams 1976, but not the ambitus (no equatorial extension for instance); distal rows of minute spines on narrow processes tip could compare with ornamentation on some Apectodinium (Costa and Downie) Lentin and Williams 1977, but paratabulation is generally not clear on Apectodinium cysts. However, in no case Spinidinium stellatum shows the characteristic quadra-type dorsal organization of the Wetzeliellaceae (2a quadra, large and broad 4"), nor the para ventral organization (1" contacts 2" and 6").
Holotype: Soncini, 1992, pl.3, figs.1-3
Locus typicus: Abdoun, Morocco
Stratum typicum: Thanetian-Ypresian
Original diagnosis: Soncini, 1992, p.335
Rounded polygonal, compressed dorsoventrally, proximochorate two-layered cyst, circumcavate (to bicavate). Short apical horn truncated, left antapical horn variable in length, pointed, right antapical reduced or absent. Broad and laterally prominent paracingulum. Numerous projections on cyst surface, variable in length and shape complexity. Tapering proximally, with pericoele often protruding into their base; solid stem short to long, narrow to broad; distal part simple, bifurcate, trifurcate or more; at any scale, every distal extremity expanding and aculeate. Paratabulation evident (except in paracingular and parasulcal areas), peridinioid ortho- (ventral side) hexa type (dorsal side). Projections in parasutural position on ventral side, in penitabular position on dorsal side, partially missing on 2a intercalary paraplate (border-side with 4") and on 3""" (borderside with paracingulum), absent in the paracingulum and the sulcal areas. Strong antapical dissymmetry, 2"""" large and almost centered, 1"""" reduced to the left antapical horn. Peri- and endo-archeopyle type la, eurydeltaform. Perioperculum commonly adnate, endoperculum adnate, rarely discernible.
Dimensions: holotype length: 95.5 µm, width: 77 µm; range length: 67-116.5 µm, width: 60.5-112 µm; processes length: 2-9.5 µm (homogeneous on each specimen); 120 specimens measured.
Original description: Soncini, 1992, p.335-336
Spinidinium stellatum cysts are two layered, the endophragm is thin and smooth, spheroidal, variably appressed to the periphragm (circumcavate to bicavate). The periphragm is generally smooth or shagrinate, but sometimes foveolate (Plate lll, 5, 6). Straight, long and simple projections are particularly well developed on the extremities of apical and antapical horn (Plate lll, 4). Paracingulum borders are also prominent, underlined by more complex projections: simple, bifid or trifid, they can be linked together proximally in a discontinuous ridge. Although they are homogeneous on a single specimen, projections show a great diversity in shape and length (Fig.7); it is then hard to call them "spines" or "processes". With short or long, narrow or broad solid stem, straight or branched, bifid, trifid, they are all distally expanded and aculeate, but the rows of minute acuminate spines are hardly discernible (Plate III, 13, 14). Anyway, the first striking feature all projections have in common is their roughly star-shaped tip (hence the species name: stellatum).
Projections are scarce on paraplates surface, but numerous in parasutural position on ventral side (Plate III, 3), and in penitabular position on dorsal side (Plate III, 1, 10, 11) (rare specimens with just few "diminutive processes" underlying paratabulation). Lack of projection on posterior margin of intercalary paraplate 2a (contact 2a/u"), and on the anterior margin of postcingular paraplate 3""" (contact 3"""/paracing.) are also diagnostic features (Fig.8). Paratabulation peridinioid, with ventral ortho-type. Dorsally, la and 3a intercalaries seem to be smaller than the six-sided 2a (hexa-type). The archeopyle (type la) is eurydeltaform (Plate III, 1), the operculum (2a) is generally adnate (Plate III, 10). The endoperculum is also adnate and eurydeltaform, sometimes discernible inside the cyst (Plate III, 4).
Affinities:
Soncini, 1992, p.336: Although it belongs clearly to the genus Spinidinium, S. stellatum differs greatly from other Spinidinium species: with the penitabular and parasutural distribution of the projections (commonly covering the surface of the cyst except on pandasutural areas on other paratabulated Spinidinium species);
- with the complexity of these projections: short to long spines (like most Spinidinium) or diminutive processes typically expanded and aculeate (very distinctive character). Some features in S. stellatum suggest morphological affinities with the Wetzeliellaceae: processes distribution could compare with some Wilsonidium Lentin and Williams 1976, but not the ambitus (no equatorial extension for instance); distal rows of minute spines on narrow processes tip could compare with ornamentation on some Apectodinium (Costa and Downie) Lentin and Williams 1977, but paratabulation is generally not clear on Apectodinium cysts. However, in no case Spinidinium stellatum shows the characteristic quadra-type dorsal organization of the Wetzeliellaceae (2a quadra, large and broad 4"), nor the para ventral organization (1" contacts 2" and 6").