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Wetzeliella lobisca
Wetzeliella lobisca (Williams and Downie, 1966) Jolley and Spinner, 1989
Originally Wetzeliella symmetrica var. lobisca, subsequently Wetzeliella symmetrica subsp. lobisca, thirdly Wetzeliella meckelfeldensis subsp. lobisca, fourthly Wetzeliella lobisca, fifthly (and now) Dracodinium lobiscum.
Holotype: Williams and Downie, 1966, pl.20, fig.3
Locus typicus: London Clay, Sheppey, England
Stratum typicum: Early Eocene
Original description: Williams and Downie, 1966, p. 196: Wetzeliella (Wetzeliella) symmetrica ssp. Iobisca
This is a variety of W. (W.) symmetrica which has a slightly reduced apical horn and the single antapical horn is offset to the right of the midventral line. It is identical with the two figured specimens of W. symmetrica symmetrica Gerlach (1961) and Hystrichosphaeridium articulatum Pastiels (1948).
Dimensions: holotype: outer shell, length 137 µm, breadth 123 µm. Capsule, length 78 µm, breadth 70 µm. Observed range: outer shell, length 25-137 µm, breadth, 118-150 µm. Capsule, length 72-80 µm, breadth 70-79 µm.
Supplemental description: Jolley and Spinner, 1989, p.369, 371
Shape: Pericyst is distinctly subpentagonal in dorso-ventral view due to its extension into five relatively large horns which range in length from l/4 to l/2 of the diameter of the pericyst. The right antapical horn is variably developed being of smaller size and shape to the left horn, or represented by a cluster of processes. The cingular and apical horns vary between l/4 and l/2 of the breadth of the pericyst, but are of unequal length. The left cingular horn is usually shorter than the right. Wall relationships: A narrow pericoel is developed which is continuous, but wider at the bases of the horns. Wall features: Numerous hollow distally open intratabular processes are scattered over the periphragm. The processes may bifurcate at the midpoint and terminate in a number of secae (4 to 8) often recurved. Evidence of paratabulation is slight, the paracingulum is indicated from the parallel arrangement of the processes on either side of an unornamented band connecting the two lateral horns and the archaeopyle. Archaeopyle: Intercalary Type I/I(2a); both the periarchaeopyle and endarchaeopyle are visible, the former is always more distinctly elongate axially than is the endarchaeopyle.
Discussion: In the studied population the endocyst varies in shape from rounded oval to sub-rhomboidal, a feature reflected in the periphragm. A parallel sided pericoel is maintained throughout. In the majority of specimens observed the right antapical is approximately half the length of the left. The apical horn is not larger than the largest cingular horn, the cingular horns themselves are long and tapering finishing in a flat distal termination. The archaeopyle is quite distinctive with the periarchaeopyle extending apically into the base of the apical horn.
The close relationship between this species and W. astra is illustrated (Fig.4) which shows the relationship between apical and cingular horn lengths. This relationship is perhaps best defined as a plexus. The delineation between the two species is apparent from this graph, including specimens attributed to both species from two separate samples. It is however evident that separation of the two species using this method may encounter difficulties at the boundary between the species. It emphasises the close relationships of the species and the tendency in W. Iobisca for cingular horns larger than the apical.
Summary of Dimensions of Population Studied in Sample Horizon C8: Length of pericyst including horns 91-131 µm, mean 107 µm; breadth of pericyst including horns 94-104 µm, mean 107 µm; length of endocyst 62-75 µm, mean 69 µm; breadth of endocyst 61-79 µm, mean 63 µm; length of apical horn 11-25 µm, mean 17 µm; length of cingular horns, left 15-31 µm, right 12-30 µm, length of antapical horns, left 15-21 µm, right 9-16 µm.
Affinities:
Jolley and Spinner, 1989, p.371-372: W. Iobisca differs from W. astra in the greater length of the periphragmal horns 15-31 µm (compared to 3-21 µm in W. astra) and the more elongate periarchaeopyle. This is related to the greater length of the apical horn in W. Iobisca 11-25 µm (compared to 6-12 µm in W. astra). Figure 4 shows a plot of length of horns in specimens of W. astra and W. Iobisca from two samples. The occurrence of W. astra and W. Iobisca, is of stratigraphical value, the former species declining in number in the younger of the samples. W. Iobisca differs from W. astroides Islam in having a smaller size, less symmetrical outline and with a narrow restricted pericoel. W. articulata differs from W. Iobisca in having a more symmetrical outline with antapical horns of equal dimensions, larger in size and a wider pericoel. W. meckelfeldensis differs from W. Iobisca by its greater size, more centrally positioned larger antapical horn, the sparsely developed ornament on the periphragm and wider pericoel. W. Iunaris is similar to W. Iobisca in size and shape of horns, but is larger in overall size. W. Iunaris lacks the secae on the processes and possesses a wider pericoel. The similarity between W. Iobisca and W. Iunaris may indicate that the latter has origins in this member of W. astra plexus. Chateauneuf and Gruas-Cavagnetto (1978) discussed possible relationship of W. meckelfeldensis with other taxa of the genus. They compared W. meckelfeldensis subsp. Iobisca with their W. meckelfeldensis group 1. The description (p.66, fig.2) and illustrations (pl.1, figs.5-8, pl.2, figs.1-3) of the groups are insufficient in the authors view to allow detailed comparison to be made, but from the limited evidence the authors suggest that W. meckelfeldensis group 2 of Chateauneuf and Gruas-Cavagnetto shows more morphological similarity to W. Iobisca as described here.
Sarjeant (1986) recorded and illustrated specimens as W. meckelfeldensis Gocht subsp. Iobisca (Williams and Downie, 1988) Costa and Downie, 1979. No description was given of the specimens. Sarjeant reported that the specimens were first included within Hystrichosphaeridium articulatum (Eisenack) Pastiels 1948 and suggested that the stratigraphic range was likely to prove identical to W. meckelfeldensis.
Originally Wetzeliella symmetrica var. lobisca, subsequently Wetzeliella symmetrica subsp. lobisca, thirdly Wetzeliella meckelfeldensis subsp. lobisca, fourthly Wetzeliella lobisca, fifthly (and now) Dracodinium lobiscum.
Holotype: Williams and Downie, 1966, pl.20, fig.3
Locus typicus: London Clay, Sheppey, England
Stratum typicum: Early Eocene
Original description: Williams and Downie, 1966, p. 196: Wetzeliella (Wetzeliella) symmetrica ssp. Iobisca
This is a variety of W. (W.) symmetrica which has a slightly reduced apical horn and the single antapical horn is offset to the right of the midventral line. It is identical with the two figured specimens of W. symmetrica symmetrica Gerlach (1961) and Hystrichosphaeridium articulatum Pastiels (1948).
Dimensions: holotype: outer shell, length 137 µm, breadth 123 µm. Capsule, length 78 µm, breadth 70 µm. Observed range: outer shell, length 25-137 µm, breadth, 118-150 µm. Capsule, length 72-80 µm, breadth 70-79 µm.
Supplemental description: Jolley and Spinner, 1989, p.369, 371
Shape: Pericyst is distinctly subpentagonal in dorso-ventral view due to its extension into five relatively large horns which range in length from l/4 to l/2 of the diameter of the pericyst. The right antapical horn is variably developed being of smaller size and shape to the left horn, or represented by a cluster of processes. The cingular and apical horns vary between l/4 and l/2 of the breadth of the pericyst, but are of unequal length. The left cingular horn is usually shorter than the right. Wall relationships: A narrow pericoel is developed which is continuous, but wider at the bases of the horns. Wall features: Numerous hollow distally open intratabular processes are scattered over the periphragm. The processes may bifurcate at the midpoint and terminate in a number of secae (4 to 8) often recurved. Evidence of paratabulation is slight, the paracingulum is indicated from the parallel arrangement of the processes on either side of an unornamented band connecting the two lateral horns and the archaeopyle. Archaeopyle: Intercalary Type I/I(2a); both the periarchaeopyle and endarchaeopyle are visible, the former is always more distinctly elongate axially than is the endarchaeopyle.
Discussion: In the studied population the endocyst varies in shape from rounded oval to sub-rhomboidal, a feature reflected in the periphragm. A parallel sided pericoel is maintained throughout. In the majority of specimens observed the right antapical is approximately half the length of the left. The apical horn is not larger than the largest cingular horn, the cingular horns themselves are long and tapering finishing in a flat distal termination. The archaeopyle is quite distinctive with the periarchaeopyle extending apically into the base of the apical horn.
The close relationship between this species and W. astra is illustrated (Fig.4) which shows the relationship between apical and cingular horn lengths. This relationship is perhaps best defined as a plexus. The delineation between the two species is apparent from this graph, including specimens attributed to both species from two separate samples. It is however evident that separation of the two species using this method may encounter difficulties at the boundary between the species. It emphasises the close relationships of the species and the tendency in W. Iobisca for cingular horns larger than the apical.
Summary of Dimensions of Population Studied in Sample Horizon C8: Length of pericyst including horns 91-131 µm, mean 107 µm; breadth of pericyst including horns 94-104 µm, mean 107 µm; length of endocyst 62-75 µm, mean 69 µm; breadth of endocyst 61-79 µm, mean 63 µm; length of apical horn 11-25 µm, mean 17 µm; length of cingular horns, left 15-31 µm, right 12-30 µm, length of antapical horns, left 15-21 µm, right 9-16 µm.
Affinities:
Jolley and Spinner, 1989, p.371-372: W. Iobisca differs from W. astra in the greater length of the periphragmal horns 15-31 µm (compared to 3-21 µm in W. astra) and the more elongate periarchaeopyle. This is related to the greater length of the apical horn in W. Iobisca 11-25 µm (compared to 6-12 µm in W. astra). Figure 4 shows a plot of length of horns in specimens of W. astra and W. Iobisca from two samples. The occurrence of W. astra and W. Iobisca, is of stratigraphical value, the former species declining in number in the younger of the samples. W. Iobisca differs from W. astroides Islam in having a smaller size, less symmetrical outline and with a narrow restricted pericoel. W. articulata differs from W. Iobisca in having a more symmetrical outline with antapical horns of equal dimensions, larger in size and a wider pericoel. W. meckelfeldensis differs from W. Iobisca by its greater size, more centrally positioned larger antapical horn, the sparsely developed ornament on the periphragm and wider pericoel. W. Iunaris is similar to W. Iobisca in size and shape of horns, but is larger in overall size. W. Iunaris lacks the secae on the processes and possesses a wider pericoel. The similarity between W. Iobisca and W. Iunaris may indicate that the latter has origins in this member of W. astra plexus. Chateauneuf and Gruas-Cavagnetto (1978) discussed possible relationship of W. meckelfeldensis with other taxa of the genus. They compared W. meckelfeldensis subsp. Iobisca with their W. meckelfeldensis group 1. The description (p.66, fig.2) and illustrations (pl.1, figs.5-8, pl.2, figs.1-3) of the groups are insufficient in the authors view to allow detailed comparison to be made, but from the limited evidence the authors suggest that W. meckelfeldensis group 2 of Chateauneuf and Gruas-Cavagnetto shows more morphological similarity to W. Iobisca as described here.
Sarjeant (1986) recorded and illustrated specimens as W. meckelfeldensis Gocht subsp. Iobisca (Williams and Downie, 1988) Costa and Downie, 1979. No description was given of the specimens. Sarjeant reported that the specimens were first included within Hystrichosphaeridium articulatum (Eisenack) Pastiels 1948 and suggested that the stratigraphic range was likely to prove identical to W. meckelfeldensis.