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Canninginopsis lindseyensis
Figures 6.8, 6.9, 7.7
Derivation of name. From Lindsey, a former Anglo-Saxon kingdom and current district of Lincolnshire.
Designation of holotype. Figures 6.8, 6.9. Sample MR11. Slide MR11(B). Coordinates P44/3. Location, Melton Ross Quarry, Lincolnshire, UK. Stratum, Bed C, Flixton Member, Welton Chalk Formation. The specimen is curated in the MPK collection of the British Geological Survey, Keyworth, Nottingham, UK, specimen number MPK 14663.
Diagnosis. An areoligeracean dinoflagellate cyst possessing tabular to penitabular thickenings that form the bases of thinner, entire septae.
Description. Small to intermediate-sized, lenticularshaped autocysts with differential development of a larger left antapical horn. A sulcal notch is present. The cyst wall is c. 1 μm thick and has a smooth to slightly reticulate surface. Tabulation is indicated by an apical archaeopyle (operculum detached) and tabular to penitabular thickenings, c. 1–2 μm high and 1–3 μm wide, that form the bases of thinner septae. The septae are c. 2–5 μm high and 1 μm wide, entire, smooth to slightly reticulate and often exhibit some longitudinal folding (‘creases’). Proximal thickenings/septae are adjacent (tabular) or separated by gaps of up to 4 μm ( penitabular). The gonyaulacoid tabulation pattern is (operculum not observed); 6II, 6c, 5–6III, ?1P, 1IIII, ?s.
Dimensions (length × width, without operculum).
Holotype: length 44.4 μm, width 54.1 μm. Other specimens (two measured): length 43.0 (46.3) 49.6 μm, width 58.9 (64.3) 69.6 μm.
Discussion. The shape, presence of a sulcal notch and a probable small postcingular 1III plate (Fig. 6.8) indicate an areoligeracean affinity (cf. Evitt 1985, text-figs 10.2, 10.6). Strongly developed tabulation is consistent with the genus Canninginopsis. Although the type species and most other accepted species often possess discontinuous ornament elements reflecting tabulation such as spines or grana, continuous septae are present on the species Canninginopsis maastrichtiensis from the Maastrichtian of Belgium and Netherlands (Slimani 1994). However, the development of gaps between septae, giving rise to penitabular ornament, is inconsistent with Canninginopsis and warrants questionable assignment to the genus. Penitabulation has been noted in the related genus Canningia, e.g. Canningia transitoria (Stover and Helby 1987, fig. 4) but its septae are coarsely perforate. Schematophora possesses entire to occasionally perforate penitabular ridges but has a spherical, non-areoligeracean shape and lacks any tabulation in the cingulum region (Deflandre and Cookson 1955; Stover and Evitt 1978). On the holotype of C.? lindseyensis, the dorsal precingular plate (3II) appears to be absent but this could be due to specimen damage. Likewise, a precingular 6II plate may be damaged. A second specimen with less well-developed or preserved septae (Fig. 7.7) indicates that six precingular plates may usually be present. The highly distinctive morphology warrants erection of a formal species, although it is acknowledged that doing so is unusual for just three specimens. Recovery and inspection of further specimens is required to fully elucidate the taxon and its generic assignment.
Stratigraphic range/occurrence. At Melton Ross, Bed C (sample -11 only).
Derivation of name. From Lindsey, a former Anglo-Saxon kingdom and current district of Lincolnshire.
Designation of holotype. Figures 6.8, 6.9. Sample MR11. Slide MR11(B). Coordinates P44/3. Location, Melton Ross Quarry, Lincolnshire, UK. Stratum, Bed C, Flixton Member, Welton Chalk Formation. The specimen is curated in the MPK collection of the British Geological Survey, Keyworth, Nottingham, UK, specimen number MPK 14663.
Diagnosis. An areoligeracean dinoflagellate cyst possessing tabular to penitabular thickenings that form the bases of thinner, entire septae.
Description. Small to intermediate-sized, lenticularshaped autocysts with differential development of a larger left antapical horn. A sulcal notch is present. The cyst wall is c. 1 μm thick and has a smooth to slightly reticulate surface. Tabulation is indicated by an apical archaeopyle (operculum detached) and tabular to penitabular thickenings, c. 1–2 μm high and 1–3 μm wide, that form the bases of thinner septae. The septae are c. 2–5 μm high and 1 μm wide, entire, smooth to slightly reticulate and often exhibit some longitudinal folding (‘creases’). Proximal thickenings/septae are adjacent (tabular) or separated by gaps of up to 4 μm ( penitabular). The gonyaulacoid tabulation pattern is (operculum not observed); 6II, 6c, 5–6III, ?1P, 1IIII, ?s.
Dimensions (length × width, without operculum).
Holotype: length 44.4 μm, width 54.1 μm. Other specimens (two measured): length 43.0 (46.3) 49.6 μm, width 58.9 (64.3) 69.6 μm.
Discussion. The shape, presence of a sulcal notch and a probable small postcingular 1III plate (Fig. 6.8) indicate an areoligeracean affinity (cf. Evitt 1985, text-figs 10.2, 10.6). Strongly developed tabulation is consistent with the genus Canninginopsis. Although the type species and most other accepted species often possess discontinuous ornament elements reflecting tabulation such as spines or grana, continuous septae are present on the species Canninginopsis maastrichtiensis from the Maastrichtian of Belgium and Netherlands (Slimani 1994). However, the development of gaps between septae, giving rise to penitabular ornament, is inconsistent with Canninginopsis and warrants questionable assignment to the genus. Penitabulation has been noted in the related genus Canningia, e.g. Canningia transitoria (Stover and Helby 1987, fig. 4) but its septae are coarsely perforate. Schematophora possesses entire to occasionally perforate penitabular ridges but has a spherical, non-areoligeracean shape and lacks any tabulation in the cingulum region (Deflandre and Cookson 1955; Stover and Evitt 1978). On the holotype of C.? lindseyensis, the dorsal precingular plate (3II) appears to be absent but this could be due to specimen damage. Likewise, a precingular 6II plate may be damaged. A second specimen with less well-developed or preserved septae (Fig. 7.7) indicates that six precingular plates may usually be present. The highly distinctive morphology warrants erection of a formal species, although it is acknowledged that doing so is unusual for just three specimens. Recovery and inspection of further specimens is required to fully elucidate the taxon and its generic assignment.
Stratigraphic range/occurrence. At Melton Ross, Bed C (sample -11 only).