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Stephodinium parvum
Stephodinium? parvum De Coninck, 1986
De Coninck, 1986 questionably included this species in Stephodinium.
Holotype: De Coninck, 1986, pl. 9, fig.21-23
Locus typicus: Woensdrecht borehole, S Netherlands
Stratum typicum: Bartonian-Rupelian
Original diagnosis: De Coninck, 1986, p. 19
The small species is characterized by an ellipsoidal, apical-antapically elongated endocyst. This endocyst is enveloped in a periphragm which lies in direct contact on the endocyst near the poles, occasionally forming a very short protrusion. Away from the polar areas, in the equatorial direction the periphragm seperates from the endocyst and forms a large equatorial belt with straight sides parallel to the axis of the endocyst. This equatorial belt is continuous and its width around the axis is constant. No interruption of the equatorial belt corresponding to a longitudinal furrow can be observed. The periphragm has a reticulous to spongy structure, especially in the equatorial belt where it is rather thick. On the polar areas it is thinner. Between the equatorial belt and the polar areas the periphragm is reduced to some strands between which empty spaces suggest at first sight a tabulation. The number of these spaces is variable (between 6 to 8 on both sides of the equatorial belt).
Dimensions of the central body: Holotype: 17.5 µm long and 10 µm wide. Other specimens: between 17 and 19µm long and 9 to 10 µm wide. Equatorial belt: Holotype: about 7 µm wide and 7 mm high. Other specimens: from 6 to 10 µm wide and 8 to 10 µm high. Overall dimensions: Holotype: 20 µm long and 22.5 µm wide. Other specimens: about 21 µm long and 22 to 30 µm wide.
Affinities:
De Coninck, 1986, p. 19: Several characteristic features of the new species correspond well to those of the genotype S. coronatum Deflandre 1935. In our S. ? parvum the equatorial extension is continuous; its "ventral" portion is not discernible. According to the modified description however of Stephodmium, given by Davey 1970 (p. 347) after studying several specimens of S. coronatum, the equatorial extension of the periphragm is ventrally in contact with the endocyst. For this reason mainly, the attribution of the new species to Stephodinium remains questionable.
De Coninck, 1986 questionably included this species in Stephodinium.
Holotype: De Coninck, 1986, pl. 9, fig.21-23
Locus typicus: Woensdrecht borehole, S Netherlands
Stratum typicum: Bartonian-Rupelian
Original diagnosis: De Coninck, 1986, p. 19
The small species is characterized by an ellipsoidal, apical-antapically elongated endocyst. This endocyst is enveloped in a periphragm which lies in direct contact on the endocyst near the poles, occasionally forming a very short protrusion. Away from the polar areas, in the equatorial direction the periphragm seperates from the endocyst and forms a large equatorial belt with straight sides parallel to the axis of the endocyst. This equatorial belt is continuous and its width around the axis is constant. No interruption of the equatorial belt corresponding to a longitudinal furrow can be observed. The periphragm has a reticulous to spongy structure, especially in the equatorial belt where it is rather thick. On the polar areas it is thinner. Between the equatorial belt and the polar areas the periphragm is reduced to some strands between which empty spaces suggest at first sight a tabulation. The number of these spaces is variable (between 6 to 8 on both sides of the equatorial belt).
Dimensions of the central body: Holotype: 17.5 µm long and 10 µm wide. Other specimens: between 17 and 19µm long and 9 to 10 µm wide. Equatorial belt: Holotype: about 7 µm wide and 7 mm high. Other specimens: from 6 to 10 µm wide and 8 to 10 µm high. Overall dimensions: Holotype: 20 µm long and 22.5 µm wide. Other specimens: about 21 µm long and 22 to 30 µm wide.
Affinities:
De Coninck, 1986, p. 19: Several characteristic features of the new species correspond well to those of the genotype S. coronatum Deflandre 1935. In our S. ? parvum the equatorial extension is continuous; its "ventral" portion is not discernible. According to the modified description however of Stephodmium, given by Davey 1970 (p. 347) after studying several specimens of S. coronatum, the equatorial extension of the periphragm is ventrally in contact with the endocyst. For this reason mainly, the attribution of the new species to Stephodinium remains questionable.