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Scaldecysta doelensis
Scaldecysta doelensis De Schepper et al., 2004, p.641, fig.12, nos.1–12; fig.13, nos.1–8.
Holotype: De Schepper et al., 2004, fig.12, nos.1–4.
Age: Pliocene.
Original description (De Schepper et al., 2004)
Diagnosis
A large species of Scaldecysta n. gen. with horns ending in solid acuminate tips. Cyst wall thin, brown in color and smooth or faintly ornamented. Apical horn approximately rectangular in outline, ends in two divergent, symmetrically distributed, usually recurved, solid tips. Two closely appressed antapical horns, divergent only near distal end, one horn always longer than other. Two pronounced lateral horns of approximate equal size. Epicyst and hypocyst triangular, largely equidimensional. Large trapezoidal archeopyle, formed by loss of single anterior intercalary plate (presumed 2a). Cingulum and sulcus not expressed. Operculum free.
Description
Large cyst, rhombic in dorsoventral outline; moderate dorsoventral compression. Wall is thin (<0.3 μm), unstratified under light microscopy, and medium to pale brown in color. Wall surface smooth or shagreenate. Epicyst and hypocyst each triangular, approximately equal in size. Five horns present: one apical, two lateral, and two antapical. Horns are extensions of central cavity and all end in unbranched solid tips. Apical horn is rectangular in dorsoventral outline, ending in two divergent, usually recurved, symmetrically distributed, solid tips. Closely appressed antapical horns diverge only near distal end of hypocyst, with one antapical horn always longer than other (Fig. 13.5–13.8). No other horns or processes observed. Archeopyle large, trapezoidal in shape, formed by loss of single anterior intercalary plate (presumed 2a). Archeopyle height and width of approximately equal dimensions. Cingulum and sulcus not expressed. No accessory sutures. Operculum free.
Etymology
Named after the village of Doel, which will probably disappear due to expansion of the Antwerp Harbor and particularly with the completion of the Deurganck Dock, where samples for this study were collected.
Type
Holotype, sample VB 31/10/00 2.9, slide p1B, England Finder reference R48/4. Kruisschans Sands Member, Lillo Formation, Verrebroek Dock; upper Lower or lower Upper Pliocene. Figure 12.1–12.4. Royal Belgian Institute of Natural Sciences, Brussels, registration number IRScN b4256.
Measurements
Holotype: length (including horns), 76 μm; width (including horns), 96 μm. Range: length (including horns), 60(84.3)104 μm (12 specimens measured); width (including horns), 77(91.3)108 μm (nine specimens measured); thickness, 24(28.8)35 μm (four specimens measured). Measurements are approximate due to frequent cyst folding.
Occurrence
Restricted to the Lillo Formation (upper Lower and/or lower Upper Pliocene) of both Deurganck Dock and Verrebroek Dock localities, lowest occurrence halfway up Oorderen Sands Member, ranging into the Kruisschans Sands Member. Also observed in the Kruisschans Sands Member at Grobbendonk, Belgium (Vandenberghe et al., 2000), and from Pliocene deposits in the Poederlee borehole, Belgium (SL, personal observation).
Comparison
See under Scaldecysta, since no other species of this genus have yet been identified.
Autecology
The restricted distribution of Scaldecysta doelensis within the shallow marine upper part of the Oorderen Sands and the inner-neritic Kruisschans Sands members (Louwye et al., in press) suggests a preference for shallow marine environments. Temperate climatic conditions prevailed during the deposition of these sequences (Louwye et al., in press).
Discussion
Cysts of this species are prone to preservational folding and to breakage of the solid tips of the horns. The archeopyle was not observed on most specimens, and when it was visible, the general outline was frequently obscured by folding of the cyst wall. The archeopyle tends to be offset slightly to the left of the apical-antapical axis. Observations on a single undistorted specimen indicate an iso-delta-planate archeopyle with reentrant angles 1∧2 and 3∧4 (s. de Verteuil and Norris, 1996, text-fig. 21, p. 101; Fig. 12.5, 12.6). It is difficult to ascertain the dorsoventral orientation of the cyst when the archeopyle is absent, as no other indicators of orientation were observed.
Holotype: De Schepper et al., 2004, fig.12, nos.1–4.
Age: Pliocene.
Original description (De Schepper et al., 2004)
Diagnosis
A large species of Scaldecysta n. gen. with horns ending in solid acuminate tips. Cyst wall thin, brown in color and smooth or faintly ornamented. Apical horn approximately rectangular in outline, ends in two divergent, symmetrically distributed, usually recurved, solid tips. Two closely appressed antapical horns, divergent only near distal end, one horn always longer than other. Two pronounced lateral horns of approximate equal size. Epicyst and hypocyst triangular, largely equidimensional. Large trapezoidal archeopyle, formed by loss of single anterior intercalary plate (presumed 2a). Cingulum and sulcus not expressed. Operculum free.
Description
Large cyst, rhombic in dorsoventral outline; moderate dorsoventral compression. Wall is thin (<0.3 μm), unstratified under light microscopy, and medium to pale brown in color. Wall surface smooth or shagreenate. Epicyst and hypocyst each triangular, approximately equal in size. Five horns present: one apical, two lateral, and two antapical. Horns are extensions of central cavity and all end in unbranched solid tips. Apical horn is rectangular in dorsoventral outline, ending in two divergent, usually recurved, symmetrically distributed, solid tips. Closely appressed antapical horns diverge only near distal end of hypocyst, with one antapical horn always longer than other (Fig. 13.5–13.8). No other horns or processes observed. Archeopyle large, trapezoidal in shape, formed by loss of single anterior intercalary plate (presumed 2a). Archeopyle height and width of approximately equal dimensions. Cingulum and sulcus not expressed. No accessory sutures. Operculum free.
Etymology
Named after the village of Doel, which will probably disappear due to expansion of the Antwerp Harbor and particularly with the completion of the Deurganck Dock, where samples for this study were collected.
Type
Holotype, sample VB 31/10/00 2.9, slide p1B, England Finder reference R48/4. Kruisschans Sands Member, Lillo Formation, Verrebroek Dock; upper Lower or lower Upper Pliocene. Figure 12.1–12.4. Royal Belgian Institute of Natural Sciences, Brussels, registration number IRScN b4256.
Measurements
Holotype: length (including horns), 76 μm; width (including horns), 96 μm. Range: length (including horns), 60(84.3)104 μm (12 specimens measured); width (including horns), 77(91.3)108 μm (nine specimens measured); thickness, 24(28.8)35 μm (four specimens measured). Measurements are approximate due to frequent cyst folding.
Occurrence
Restricted to the Lillo Formation (upper Lower and/or lower Upper Pliocene) of both Deurganck Dock and Verrebroek Dock localities, lowest occurrence halfway up Oorderen Sands Member, ranging into the Kruisschans Sands Member. Also observed in the Kruisschans Sands Member at Grobbendonk, Belgium (Vandenberghe et al., 2000), and from Pliocene deposits in the Poederlee borehole, Belgium (SL, personal observation).
Comparison
See under Scaldecysta, since no other species of this genus have yet been identified.
Autecology
The restricted distribution of Scaldecysta doelensis within the shallow marine upper part of the Oorderen Sands and the inner-neritic Kruisschans Sands members (Louwye et al., in press) suggests a preference for shallow marine environments. Temperate climatic conditions prevailed during the deposition of these sequences (Louwye et al., in press).
Discussion
Cysts of this species are prone to preservational folding and to breakage of the solid tips of the horns. The archeopyle was not observed on most specimens, and when it was visible, the general outline was frequently obscured by folding of the cyst wall. The archeopyle tends to be offset slightly to the left of the apical-antapical axis. Observations on a single undistorted specimen indicate an iso-delta-planate archeopyle with reentrant angles 1∧2 and 3∧4 (s. de Verteuil and Norris, 1996, text-fig. 21, p. 101; Fig. 12.5, 12.6). It is difficult to ascertain the dorsoventral orientation of the cyst when the archeopyle is absent, as no other indicators of orientation were observed.