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Impletosphaeridium banterwickense
Impletosphaeridium banterwickense sp. nov., Pearce, M. A., 2018, p. 82-84
Holotype: Pearce, M. A., 2018, Pl. 5, figs. 7–9.
Type locality and horizon: Middle Chalk Formation, New Pit Chalk Member, Terebratulina lata Zone
Stratigraphic range: uppermost Cenomanian to Middle Coniacian
Original description: Pearce, M. A., 2018:
Diagnosis:
A species of Impletosphaeridium possessing spines that terminate distally into a simple bifurcation with endings of equal length.
Description:
A small chorate dinoflagellate cyst with a sub-rounded body.
Wall: composed of a finely granular autophragm from which arises evenly distributed, non-tabular solid spines, which terminate in a short bifurcation.
No expression of the cingulum or sulcus is present.
Archaeopyle: apical, Type tA, with a zig-zag margin and accessory sutures
The operculum may be attached but more usually detached.
Dimensions:
Holotype, central body w/ l = 46 × 39 μm, maximum process length = 12 μm.
Paratype: central body w/ l = 46 × 39 μm, maximum process length = 14 μm.
Range: central body w/ l = 35(41)47 × 29(36)43 μm, maximum process length = 10(13)16 μm.
Twenty specimens measured.
Affinities/Comparison:
Impletosphaeridium furcillatum (Prössl, 1990 ex Prössl, 1992) Williams et al., 1998 differs in
possessing thicker bifurcate to multifurate processes, while I. ligospinosum (de Coninck, 1969) Islam, 1983 differs in possessing bifurcations of unequal length. In I. Varispinosum (Sarjeant, 1959) Islam, 1993, the spines are more numerous and differ in being occasionally simple but more frequently bifurcate, clavate or “hammer-headed”. The only similar species of comparable age is I. williamsii (Boltenhagen, 1977) Islam, 1993; although it possesses acuminate to bifurcate processes, many of the latter style more closely resemble flared process endings than bifurcating spines. Species of Downiesphaeridium differ in possessing hollow (and distally closed) processes, the closest species of which is D. aciculare (Davey, 1969) Islam, 1993, which differs further by possessing wider (although relatively thin), blade-
like processes. According to Davey (1969), the processes of Downiesphaeridium aciculare are always pointed distally and occasionally bear small subsidiary spines near their extremities. In I. banterwickense sp. nov., the subsidiary spines occur at the extremity and are significantly longer.
Holotype: Pearce, M. A., 2018, Pl. 5, figs. 7–9.
Type locality and horizon: Middle Chalk Formation, New Pit Chalk Member, Terebratulina lata Zone
Stratigraphic range: uppermost Cenomanian to Middle Coniacian
Original description: Pearce, M. A., 2018:
Diagnosis:
A species of Impletosphaeridium possessing spines that terminate distally into a simple bifurcation with endings of equal length.
Description:
A small chorate dinoflagellate cyst with a sub-rounded body.
Wall: composed of a finely granular autophragm from which arises evenly distributed, non-tabular solid spines, which terminate in a short bifurcation.
No expression of the cingulum or sulcus is present.
Archaeopyle: apical, Type tA, with a zig-zag margin and accessory sutures
The operculum may be attached but more usually detached.
Dimensions:
Holotype, central body w/ l = 46 × 39 μm, maximum process length = 12 μm.
Paratype: central body w/ l = 46 × 39 μm, maximum process length = 14 μm.
Range: central body w/ l = 35(41)47 × 29(36)43 μm, maximum process length = 10(13)16 μm.
Twenty specimens measured.
Affinities/Comparison:
Impletosphaeridium furcillatum (Prössl, 1990 ex Prössl, 1992) Williams et al., 1998 differs in
possessing thicker bifurcate to multifurate processes, while I. ligospinosum (de Coninck, 1969) Islam, 1983 differs in possessing bifurcations of unequal length. In I. Varispinosum (Sarjeant, 1959) Islam, 1993, the spines are more numerous and differ in being occasionally simple but more frequently bifurcate, clavate or “hammer-headed”. The only similar species of comparable age is I. williamsii (Boltenhagen, 1977) Islam, 1993; although it possesses acuminate to bifurcate processes, many of the latter style more closely resemble flared process endings than bifurcating spines. Species of Downiesphaeridium differ in possessing hollow (and distally closed) processes, the closest species of which is D. aciculare (Davey, 1969) Islam, 1993, which differs further by possessing wider (although relatively thin), blade-
like processes. According to Davey (1969), the processes of Downiesphaeridium aciculare are always pointed distally and occasionally bear small subsidiary spines near their extremities. In I. banterwickense sp. nov., the subsidiary spines occur at the extremity and are significantly longer.