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Selenopemphix islandensis
Selenopemphix islandensis Verhoeven and Louwye, 2012, p.13–16,18, pl.1, figs.1–12: pl.2, figs.1–12; text-figs.3A–B,4A. Holotype: Verhoeven and Louwye, 2012, pl.1, figs.1–3. Age: early Pliocene.
Original description (Verhoeven & Louwye, 2012)
Holotype. Plate 1; figures 1–3, slide WP 22 (England Finder co-ordinates: K48-1), Serripes Zone, Tjörnes beds, northern Iceland.
Repository. Royal Belgian Institute of Natural Sciences (Brussels, Belgium), catalogue number IRSNB b5759
Derivation of name. ‘Islandensis’ refers to ‘derived from Iceland’. The new species is observed for the first time in the marine deposits of the Serripes Zone in the Tjörnes section.
Diagnosis. An autophragmal, thin-walled protoperidiniacean cyst with a blunt apical horn. The cyst is polar compressed and has a reniform ambitus in apical view. The cyst wall is psilate. The cingular margin is well developed and dorsally and ventro-laterally ornamented with simple or occasionally bifurcating processes which are distally serrate, acuminate or expanded. The ornamentation of the cingular margin is typically absent over a short distance at the ventro-lateral sides, where the cingular margin is also considerably reduced. Cingular margins at the ventral sides are well developed and ornamented with a large, fan-shaped process. The tabulation is only reflected by the broad cingulum and the anterior intercalary archeopyle with rounded angles. Operculum adnate, occasionally free.
Description. The cyst possesses a thin psilate wall with a thickness of less than 0.5 μm. The wall is autophragmal and usually has a pale-brown colour. However, hyaline specimens are often encountered when the preservation was not optimal. The cyst is polar compressed and has a reniform outline in apical/antapical view. A narrow, blunt apical horn is present on the epicyst (Plate 1, figures 2, 5 and 8; Plate 2, figure 6). Antapical horns are absent. The well-developed cingulum is broad and has a width of c. 10–15 μm, and accounts for almost 50% of the total cyst height. The cingulum appears planar and is clearly interrupted in the sulcal area. The wide cingular margins are for the greater part of the circumference ornamented with processes of varying size and shape. The greater part of the processes is to a varying degree joined proximally. The morphology of the processes is tapering to nearly cylindrical. The distal ends of the processes are slightly serrated, acuminate or expanded. Processes bifurcate occasionally. The ornamentation is typically absent over a short distance of 5–10 μm at the ventro-lateral sides and in the sulcal area. The cingular margin between the ventro-lateral sides and the sulcal area is more strongly developed and is ornamented with a wide and large, sometimes asymmetrical, fan-shaped process. The process is distally irregular indented. Two pairs of asymmetrical processes are occasionally observed on a few specimens. No correlation is observed between the size of the cysts and the size of the latter processes (Figure 3A), but a clear size difference between the small dorsal processes and thelarger fan-shaped processes is always present although no exact ratio between the two sizes is found (Figure 3B). The archeopyle is formed by the release of a single anterior intercalary plate. The operculum is mostly adnate and only occasionally free. The angles of the operculum are rounded. The archeopyle is offset to the left on the dorsal side. The archeopyle and the cingulum are the only indications of tabulation.
Dimension. Maximum equatorial cyst diameter without processes: 42.8 (50.5) 64.7 μm. Minimum equatorial cyst diameter without processes: 25.1 (33.6) 44.1 μm. Dorsal process length: 1.5 (3.1) 4.8 μm. Width of the base of the first ventral arch, closest to the sulcus: 3.0 (9.6) 16.9 μm. Length of the first fan-shaped process: 2.4 (6.8) 12.1 μm. The well-developed cingulum is broad and has a width of c. 10–15 μm. Measurement based on 25 specimens.
Remarks. Selenopemphix islandensis sp. nov. is often overlooked during microscopic analysis because of its very pale, thin wall which folds readily.
Type locality. Lower Pliocene Serripes Zone, Tjörnesbeds, Tjörnes Peninsula, northern Iceland. Selenopemphix islandensis sp. nov. is recorded in the upper part of the Tjörnes beds from the base (unit 13 of Bárdason 1925) to halfway through the Serripes Zone (unit 22 of Bárdason 1925).
Comparisons. The general outline and process morphology of Selenopemphix islandensis sp. nov. is reminiscent of the outline and the process morphology of Selenopemphix brevispinosa, Selenopemphix conspicua, Selenopemphix coronata, Selenopemphix dionaeacysta and Selenopemphix selenoides (Figure 4; Plate 3). The new species has the strong polar compression, the reniform outline in apical/antapical view, the narrow apical horn and the presence of processes restricted to the cingular margins in common with the latter species. The adcingular processes of Selenopemphix sp. 3 of Head and Norris (1989) are comparable to the fan-shaped processes of Selenopemphix islandensis sp. nov., but the latter species possesses a more circular outline in apical/antapical view (Plate 3, figures 3, 4; Figure 4). The relatively wide processes (3–4 μm breadth) of Selenopemphix conspicua (de Verteuil and Norris 1992; Figure 4) are morphologically more or less comparable to the processes present on the dorsal side of Selenopemphix islandensis sp. nov. However, the processes of Selenopemphix conspicua are more or less equally spaced and continuously present over the entire cingular margin, which however is not the case on Selenopemphix islandensis sp. nov. Selenopemphix dionaeacysta (Plate 3, figures 1, 2; Figure 4) possesses a broad range of process morphologies, but the processes are more or less of equal dimensions.
The cingular ornamentation of Selenopemphix sp. 3 of Head and Norris (1989) is formed by a continuous ridge with only an interruption in the sulcal area (Plate3, figures 3–4; Figure 4). In contrast, the presence of the fan-shaped membranes on Selenopemphix islandensis sp. nov. is limited to the ventral side and never forms a continuous membrane. Furthermore, only small, simple processes are observed on Selenopemphix sp. 3 of Head and Norris (1989). Selenopemphix sp. 3 of Head and Norris (1989) also possesses two small, sharp antapical horns (Plate 3, figure 4; Figure 4), whereas no antapical horns are observed on Selenopemphix islandensis sp. nov. Selenopemphix coronata possesses simple, evenly distributed, distally bifurcating processes of equal length. The distal tips of the bifurcations are typically joined (Plate 3, figures 9, 10; Figure 4). The latter species furthermore possesses a well-pronounced apical horn and two small, antapical horns.
The cingular ornamentation of Selenopemphix islandensis sp. nov. is comparable to the ornamentation of Selenopemphix selenoides. The latter species however possesses a deep sulcus (Plate 3, figures 11, 12; Figure 4) and a supplementary perforate ridge on the hypocyst.
Original description (Verhoeven & Louwye, 2012)
Holotype. Plate 1; figures 1–3, slide WP 22 (England Finder co-ordinates: K48-1), Serripes Zone, Tjörnes beds, northern Iceland.
Repository. Royal Belgian Institute of Natural Sciences (Brussels, Belgium), catalogue number IRSNB b5759
Derivation of name. ‘Islandensis’ refers to ‘derived from Iceland’. The new species is observed for the first time in the marine deposits of the Serripes Zone in the Tjörnes section.
Diagnosis. An autophragmal, thin-walled protoperidiniacean cyst with a blunt apical horn. The cyst is polar compressed and has a reniform ambitus in apical view. The cyst wall is psilate. The cingular margin is well developed and dorsally and ventro-laterally ornamented with simple or occasionally bifurcating processes which are distally serrate, acuminate or expanded. The ornamentation of the cingular margin is typically absent over a short distance at the ventro-lateral sides, where the cingular margin is also considerably reduced. Cingular margins at the ventral sides are well developed and ornamented with a large, fan-shaped process. The tabulation is only reflected by the broad cingulum and the anterior intercalary archeopyle with rounded angles. Operculum adnate, occasionally free.
Description. The cyst possesses a thin psilate wall with a thickness of less than 0.5 μm. The wall is autophragmal and usually has a pale-brown colour. However, hyaline specimens are often encountered when the preservation was not optimal. The cyst is polar compressed and has a reniform outline in apical/antapical view. A narrow, blunt apical horn is present on the epicyst (Plate 1, figures 2, 5 and 8; Plate 2, figure 6). Antapical horns are absent. The well-developed cingulum is broad and has a width of c. 10–15 μm, and accounts for almost 50% of the total cyst height. The cingulum appears planar and is clearly interrupted in the sulcal area. The wide cingular margins are for the greater part of the circumference ornamented with processes of varying size and shape. The greater part of the processes is to a varying degree joined proximally. The morphology of the processes is tapering to nearly cylindrical. The distal ends of the processes are slightly serrated, acuminate or expanded. Processes bifurcate occasionally. The ornamentation is typically absent over a short distance of 5–10 μm at the ventro-lateral sides and in the sulcal area. The cingular margin between the ventro-lateral sides and the sulcal area is more strongly developed and is ornamented with a wide and large, sometimes asymmetrical, fan-shaped process. The process is distally irregular indented. Two pairs of asymmetrical processes are occasionally observed on a few specimens. No correlation is observed between the size of the cysts and the size of the latter processes (Figure 3A), but a clear size difference between the small dorsal processes and thelarger fan-shaped processes is always present although no exact ratio between the two sizes is found (Figure 3B). The archeopyle is formed by the release of a single anterior intercalary plate. The operculum is mostly adnate and only occasionally free. The angles of the operculum are rounded. The archeopyle is offset to the left on the dorsal side. The archeopyle and the cingulum are the only indications of tabulation.
Dimension. Maximum equatorial cyst diameter without processes: 42.8 (50.5) 64.7 μm. Minimum equatorial cyst diameter without processes: 25.1 (33.6) 44.1 μm. Dorsal process length: 1.5 (3.1) 4.8 μm. Width of the base of the first ventral arch, closest to the sulcus: 3.0 (9.6) 16.9 μm. Length of the first fan-shaped process: 2.4 (6.8) 12.1 μm. The well-developed cingulum is broad and has a width of c. 10–15 μm. Measurement based on 25 specimens.
Remarks. Selenopemphix islandensis sp. nov. is often overlooked during microscopic analysis because of its very pale, thin wall which folds readily.
Type locality. Lower Pliocene Serripes Zone, Tjörnesbeds, Tjörnes Peninsula, northern Iceland. Selenopemphix islandensis sp. nov. is recorded in the upper part of the Tjörnes beds from the base (unit 13 of Bárdason 1925) to halfway through the Serripes Zone (unit 22 of Bárdason 1925).
Comparisons. The general outline and process morphology of Selenopemphix islandensis sp. nov. is reminiscent of the outline and the process morphology of Selenopemphix brevispinosa, Selenopemphix conspicua, Selenopemphix coronata, Selenopemphix dionaeacysta and Selenopemphix selenoides (Figure 4; Plate 3). The new species has the strong polar compression, the reniform outline in apical/antapical view, the narrow apical horn and the presence of processes restricted to the cingular margins in common with the latter species. The adcingular processes of Selenopemphix sp. 3 of Head and Norris (1989) are comparable to the fan-shaped processes of Selenopemphix islandensis sp. nov., but the latter species possesses a more circular outline in apical/antapical view (Plate 3, figures 3, 4; Figure 4). The relatively wide processes (3–4 μm breadth) of Selenopemphix conspicua (de Verteuil and Norris 1992; Figure 4) are morphologically more or less comparable to the processes present on the dorsal side of Selenopemphix islandensis sp. nov. However, the processes of Selenopemphix conspicua are more or less equally spaced and continuously present over the entire cingular margin, which however is not the case on Selenopemphix islandensis sp. nov. Selenopemphix dionaeacysta (Plate 3, figures 1, 2; Figure 4) possesses a broad range of process morphologies, but the processes are more or less of equal dimensions.
The cingular ornamentation of Selenopemphix sp. 3 of Head and Norris (1989) is formed by a continuous ridge with only an interruption in the sulcal area (Plate3, figures 3–4; Figure 4). In contrast, the presence of the fan-shaped membranes on Selenopemphix islandensis sp. nov. is limited to the ventral side and never forms a continuous membrane. Furthermore, only small, simple processes are observed on Selenopemphix sp. 3 of Head and Norris (1989). Selenopemphix sp. 3 of Head and Norris (1989) also possesses two small, sharp antapical horns (Plate 3, figure 4; Figure 4), whereas no antapical horns are observed on Selenopemphix islandensis sp. nov. Selenopemphix coronata possesses simple, evenly distributed, distally bifurcating processes of equal length. The distal tips of the bifurcations are typically joined (Plate 3, figures 9, 10; Figure 4). The latter species furthermore possesses a well-pronounced apical horn and two small, antapical horns.
The cingular ornamentation of Selenopemphix islandensis sp. nov. is comparable to the ornamentation of Selenopemphix selenoides. The latter species however possesses a deep sulcus (Plate 3, figures 11, 12; Figure 4) and a supplementary perforate ridge on the hypocyst.