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Impagidinium pentahedrias
Impagidinium pentahedrias Damassa, 1979
Holotype: Damassa, 1979, pl.3, fig.25; Jan du Chene et al., 1986, pl.59, figs.7-8
Locus typicus: Coastal Belt, Franciscan Complex, California
Straum typicum: ?Danian
Age: Early Paleocene
Original diagnosis: Damassa 1979, p. 202: Impagidinium pentahedrias
Subspherical to ellipsoidal cysts gonyaulacacean paratabulation indicated by parasutural septa. Sixth precingular paraplate pentagonal first and fourth apical paraplates elongate and longitudinally parallel. Surface of cyst distinctly granulate. Sulcal paraplates not delineated by septa except for partial indication of the posterior sulcal paraplate.
Description: Damassa 1979, p. 202, 204: Impagidinium pentahedrias
Cyst subspherical to ellipsoidal, wall 2.5-3 µm thick. Length (exclusive of septa) 51-67µm (mean = 62 µm, of 12 specimens), width 43-59µm (mean = 52 µm, of 12 specimens). Gonyaulacacean paratabulation indicated by parasutural septa. Septa thin, transparent, up to 12 Ám in height, may be perforate. Surface of cyst has a densely granulate texture. Paraplate shapes are more or less standard gonyaulacacean. 6 " is pentagonal and slightly reduced in size relative to the other precingular paraplates. I" and 4" are elongate, longitudinally parallel; 4" is slightly smaller than 1 ". Septum between these paraplates generally completely developed, and paraplates 2 " and 3 " about equal in size. Sulcal paraplates not delineated except for ps, which together with paraplates 1 " " and lp, may be indicated by partially developed septa; lp smaller than ps. Ends of paracingulum offset a distance about equal to the width of the paracingulum. Precingular archeopyle slightly reduced; formed by loss of the third precingular paraplate. Loss of operculum occurs within the borders of 3 ", leaving the parasutural septa intact on the cyst. Operculum simple, free.
Paratabulation: ?pr, 4 ", 6 ", 6c, lp, ps, 5 " ", 1 " ". Inferred thecal tabulation: pr, 4", 6", 6c, 5s, lp, 6 " ", 1 " ".
Remarks: Impagidinium pentahedrias is unusual among species of this genus in having a pentagonal sixth precingular paraplate, while others are characterized by a triangular 6" (Stover and Evitt, 1978). However, like other species attributed to Impagidinium, 1. pentahedrias has elongate and longitudinally parallel first and fourth apical paraplates. These features of paratabulation allow separation of I. pentahedrias from closely similar species. I. maculatum (Cookson and Eisenack) Stover and Evitt 1978, I. elegans (Cookson and Eisenack) Stover and Evitt 1978, and Leptodinium multiplexum Wall and Dale 1968 are similar to I. pentahedrias in wall surface texture, but differ in having the characteristic triangular sixth precingular paraplate. I. elegans is decidedly spherical, and the posterior sulcal paraplate is completely delineated by septa. In addition, Cookson and Eisenack "s (1965, p . 123- 124) description suggests that fusion of the first and fourth apical paraplates is a consistent feature of I. elegans (paratabulation given as 3 ", 6 ", 5 " ", 1 p, 1 " ", Cookson and Eisenack, 1965, p. 123). Leptodinium multiplexum (described from the Pleistocene of England), also exhibits fusion of the first and fourth apical paraplates. I. maculatum may also be distinguished from I. pentahedrias by the complete delineation of the posterior sulcal paraplate. The degree of septal development in the parasulcal region of I. pentahedrias is slightly variable, particularly along the margins of paraplates 1 " ", l p and ps. The septum between the first and fourth apical paraplates generally is completely developed, and the configuration of the apical paraplates indicates the presence of a preapical paraplate as well. Material and occurrence: PL 4764, 60 specimens.
Holotype: Damassa, 1979, pl.3, fig.25; Jan du Chene et al., 1986, pl.59, figs.7-8
Locus typicus: Coastal Belt, Franciscan Complex, California
Straum typicum: ?Danian
Age: Early Paleocene
Original diagnosis: Damassa 1979, p. 202: Impagidinium pentahedrias
Subspherical to ellipsoidal cysts gonyaulacacean paratabulation indicated by parasutural septa. Sixth precingular paraplate pentagonal first and fourth apical paraplates elongate and longitudinally parallel. Surface of cyst distinctly granulate. Sulcal paraplates not delineated by septa except for partial indication of the posterior sulcal paraplate.
Description: Damassa 1979, p. 202, 204: Impagidinium pentahedrias
Cyst subspherical to ellipsoidal, wall 2.5-3 µm thick. Length (exclusive of septa) 51-67µm (mean = 62 µm, of 12 specimens), width 43-59µm (mean = 52 µm, of 12 specimens). Gonyaulacacean paratabulation indicated by parasutural septa. Septa thin, transparent, up to 12 Ám in height, may be perforate. Surface of cyst has a densely granulate texture. Paraplate shapes are more or less standard gonyaulacacean. 6 " is pentagonal and slightly reduced in size relative to the other precingular paraplates. I" and 4" are elongate, longitudinally parallel; 4" is slightly smaller than 1 ". Septum between these paraplates generally completely developed, and paraplates 2 " and 3 " about equal in size. Sulcal paraplates not delineated except for ps, which together with paraplates 1 " " and lp, may be indicated by partially developed septa; lp smaller than ps. Ends of paracingulum offset a distance about equal to the width of the paracingulum. Precingular archeopyle slightly reduced; formed by loss of the third precingular paraplate. Loss of operculum occurs within the borders of 3 ", leaving the parasutural septa intact on the cyst. Operculum simple, free.
Paratabulation: ?pr, 4 ", 6 ", 6c, lp, ps, 5 " ", 1 " ". Inferred thecal tabulation: pr, 4", 6", 6c, 5s, lp, 6 " ", 1 " ".
Remarks: Impagidinium pentahedrias is unusual among species of this genus in having a pentagonal sixth precingular paraplate, while others are characterized by a triangular 6" (Stover and Evitt, 1978). However, like other species attributed to Impagidinium, 1. pentahedrias has elongate and longitudinally parallel first and fourth apical paraplates. These features of paratabulation allow separation of I. pentahedrias from closely similar species. I. maculatum (Cookson and Eisenack) Stover and Evitt 1978, I. elegans (Cookson and Eisenack) Stover and Evitt 1978, and Leptodinium multiplexum Wall and Dale 1968 are similar to I. pentahedrias in wall surface texture, but differ in having the characteristic triangular sixth precingular paraplate. I. elegans is decidedly spherical, and the posterior sulcal paraplate is completely delineated by septa. In addition, Cookson and Eisenack "s (1965, p . 123- 124) description suggests that fusion of the first and fourth apical paraplates is a consistent feature of I. elegans (paratabulation given as 3 ", 6 ", 5 " ", 1 p, 1 " ", Cookson and Eisenack, 1965, p. 123). Leptodinium multiplexum (described from the Pleistocene of England), also exhibits fusion of the first and fourth apical paraplates. I. maculatum may also be distinguished from I. pentahedrias by the complete delineation of the posterior sulcal paraplate. The degree of septal development in the parasulcal region of I. pentahedrias is slightly variable, particularly along the margins of paraplates 1 " ", l p and ps. The septum between the first and fourth apical paraplates generally is completely developed, and the configuration of the apical paraplates indicates the presence of a preapical paraplate as well. Material and occurrence: PL 4764, 60 specimens.