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Batiacasphaera variabilis
Plate 31, Figures 1-3, 5, 6, 9, 10, 13
Holotype: Plate 31, Figures 5, 6
Paratype: Plate 31, Figure 13
Type Locality: Well 14/19-19 at 8715.50 ft (conventional core chip), early Barremian.
Holotype: Well 14/19-19 at 8715.50 ft E.F. K34.2.
Paratype: Well 14/19-19 at 8769.70 ft E.F. H43.3.
Derivation of Name: From the Latin variabilis, changeable - in reference to the varied surface ornament of this species.
Diagnosis: A small, spheroidal dinocyst with a tetratabular apical archeopyle and without accessory archeopyle sutures. Operculum usually lost, but often present. Surface ornament of even height completely covers the cyst and varies from numerous, very short, spatulate to “t-shaped” spines to complete, low rugulation; the ornament type is consistent over individual specimens. On some specimens, some spines may be joined by delicate cross-bars, at or below the spine tips.
Dimensions: Holotype (polar orientation): 51 × 51 μm
Paratype (operculum displaced): Length – 61 μm.Width – 56 μm
Overall: 58 (50) 43 μm × 61 (52) 46 μm
Specimens Measured: 21
Remarks: This small, robust species was observed in very large numbers in the early Barremian, palynofloral Subzone LKP17.1, with its acme occurrence between 8806.90 ft and 8765.00 ft in well 14/19-19 (Fig. 9); at its peak occurrence (8783.70 ft ) it constituted over 50% of the total assemblage. Abundant B. variabilis were also recorded in well 14/19-21 at the same level, but in that case restricted to the 10303.50 ft sample (Fig. 11).
The high abundance of this species has allowed a clear assessment of its morphological range and, although its size, spheroidal shape, wall thickness, etc. remain remarkably consistent, the surface ornament varies significantly from spatulate, very short spines to a complete, low rugulation. These variations can, therefore, be regarded as within a single population. The flat, t-shaped spines observed in some of the “simpler” variants are similar to the flat supporting-structures described by Davey in Cassiculosphaeridia magna (Davey 1974, p. 46), particularly well-illustrated in his Plate 2, Figs. 3, 4.
The surface ornament exhibited by B. variabilis is similar to that in Escharisphaeridia rudis Davies 1983. Although the latter species appears to have a wider range of ornament, from granules or verrucae to an imperfect reticulum (see further comments under Sentusidinium, below), it does not appear to possess very short, spatulate spines or the delicate cross-bars joining them, both typical of B. variabilis.
Specimens assigned to Membranosphaera sp. A in Davey 1979b (p. 557, Plate 4, Figs. 8-12) are similar to B. variabilis in having short “spines which vary in width, up to about 1 μm, and broaden distally where they sometimes bifurcate and link with adjoining ones”. Davey’s illustrations, particularly his Plate 4, Figs. 8 and 11, suggest a “t-shaped” spine morphology and distal linkage similar to that in B. variabilis. However, characteristics of Membranosphaera sp. A not observed in B. variabilis include ornament reduction in mid-dorsal and mid-ventral areas and longitudinal alignment of crest-like structures, particularly towards the lateral margins of the cyst.
Batiacasphaera mica Harding 1990 ex Harding in Williams et al. 1998 was recorded by Harding (1990) from the late Hauterivian to late Barremian at Speeton and Gott. It bears some superficial resemblance to B. variabilis but differs in having a granular surface with granules varying in size on individual specimens, often coarser along cingular margins (see Plate 32, Figs. 3, 4, 8, 12, 15 here).
Holotype: Plate 31, Figures 5, 6
Paratype: Plate 31, Figure 13
Type Locality: Well 14/19-19 at 8715.50 ft (conventional core chip), early Barremian.
Holotype: Well 14/19-19 at 8715.50 ft E.F. K34.2.
Paratype: Well 14/19-19 at 8769.70 ft E.F. H43.3.
Derivation of Name: From the Latin variabilis, changeable - in reference to the varied surface ornament of this species.
Diagnosis: A small, spheroidal dinocyst with a tetratabular apical archeopyle and without accessory archeopyle sutures. Operculum usually lost, but often present. Surface ornament of even height completely covers the cyst and varies from numerous, very short, spatulate to “t-shaped” spines to complete, low rugulation; the ornament type is consistent over individual specimens. On some specimens, some spines may be joined by delicate cross-bars, at or below the spine tips.
Dimensions: Holotype (polar orientation): 51 × 51 μm
Paratype (operculum displaced): Length – 61 μm.Width – 56 μm
Overall: 58 (50) 43 μm × 61 (52) 46 μm
Specimens Measured: 21
Remarks: This small, robust species was observed in very large numbers in the early Barremian, palynofloral Subzone LKP17.1, with its acme occurrence between 8806.90 ft and 8765.00 ft in well 14/19-19 (Fig. 9); at its peak occurrence (8783.70 ft ) it constituted over 50% of the total assemblage. Abundant B. variabilis were also recorded in well 14/19-21 at the same level, but in that case restricted to the 10303.50 ft sample (Fig. 11).
The high abundance of this species has allowed a clear assessment of its morphological range and, although its size, spheroidal shape, wall thickness, etc. remain remarkably consistent, the surface ornament varies significantly from spatulate, very short spines to a complete, low rugulation. These variations can, therefore, be regarded as within a single population. The flat, t-shaped spines observed in some of the “simpler” variants are similar to the flat supporting-structures described by Davey in Cassiculosphaeridia magna (Davey 1974, p. 46), particularly well-illustrated in his Plate 2, Figs. 3, 4.
The surface ornament exhibited by B. variabilis is similar to that in Escharisphaeridia rudis Davies 1983. Although the latter species appears to have a wider range of ornament, from granules or verrucae to an imperfect reticulum (see further comments under Sentusidinium, below), it does not appear to possess very short, spatulate spines or the delicate cross-bars joining them, both typical of B. variabilis.
Specimens assigned to Membranosphaera sp. A in Davey 1979b (p. 557, Plate 4, Figs. 8-12) are similar to B. variabilis in having short “spines which vary in width, up to about 1 μm, and broaden distally where they sometimes bifurcate and link with adjoining ones”. Davey’s illustrations, particularly his Plate 4, Figs. 8 and 11, suggest a “t-shaped” spine morphology and distal linkage similar to that in B. variabilis. However, characteristics of Membranosphaera sp. A not observed in B. variabilis include ornament reduction in mid-dorsal and mid-ventral areas and longitudinal alignment of crest-like structures, particularly towards the lateral margins of the cyst.
Batiacasphaera mica Harding 1990 ex Harding in Williams et al. 1998 was recorded by Harding (1990) from the late Hauterivian to late Barremian at Speeton and Gott. It bears some superficial resemblance to B. variabilis but differs in having a granular surface with granules varying in size on individual specimens, often coarser along cingular margins (see Plate 32, Figs. 3, 4, 8, 12, 15 here).