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Ctenidodinium fuscibasilarum
Ctenidodinium fuscibasilarum Riding and Helby, 2001d, p.71-72, figs.4A-L.
Holotype: Riding and Helby, 2001d, figs.4J-K.
Age: Mid-Late Callovian.
Original description (Riding and Helby, 2001d):
Derivation of name: From the Latin fuscus, meaning dark or swarthy and basilaris meaning at the base. This refers to the prominent dark, thickened antapical (1’’’’) paraplate.
Holotype and type locality: Figures 4J-K, CPC 35368, Undan-3 well, conventional core sample at 3057.00m.
Stratigraphical distribution: Ctenidodinium fuscibasilarum has been recorded from Middle to Upper Callivian starta of the Timor Sea region. It ranges from the Wanaea digitate Zone (7bi) to the middle Rignaudella aemula Zone (7aiiaii) (Foster, this volume; Helby and Partridge, in prep.).
A species of Ctenidodinium, which is elongate subhexagonal in dorsoventral outline and with or without a small apical protuberance. Autophragm thin, smooth to occasionally microscabrate axcept the antapical paraplate, which has significantly thicker and darker autophragm. Paratabulatio fully indicated by low parasutural ridges, which may be surmounted by short, solid, slender spines or denticles. The spines and/or denticles are sharply pointed or bifurcate. Gonal spines are consistently present on the antapical paraplate, which normally is also characteristic by closely inserted intergonal spines. Elsewhere on the cyst, particularly on paraplates of the precingular and postcingular series, spines are sparse, irregularly developed and/ or commonly absent.
Dimensions (µm; n=37): Min.(Mean)Max.
Length of cyst excl. spines: 61(73)86
Width of cyst body at paracingulum: 54(70)94
Width of antapical paraplate excl. spines: 19(33)44
Length of parasutural spines (mainly on 1’’’’): 3(7)16
The measured specimens are from conventional core samles in undan-3 well at 3048.00m and 3057.00m.
Comments: The most characteristic feature of Ctenidodinium fuscibasilarum is the relatively dark, thickened antapical (1’’’’) paraplate which is normally surrounded by spines or processes (Fig. 4). The preferential thickening of a single paraplate is extremely unusual among dinoflagellate cysts and was hitherto unknown in this genus. The spines are longer and more numerous closer to the antapex and the gonal spines around the 1’’’’ paraplate are longest. This lengthening is typical of Ctenidodinium and other gonyaulacalean genera. The spines/denticles other than around the 1’’’’ paraplate are irregular and short (up to 2µm-5µm, when present). The parasutural ridges are highest around the paracingulum (1-2µm) n=and lowest in the antapical area. Around the apical series, they may occasionally be discontinuous. The specie sis normally elongate , however the outline is somewhat variable and forms which are wider than long have been occasionally observed. Most forms have the paracingulum inserted equatorially, but in some forms the hypocyst is longer than the epicyst. The paratabulation pattern is consistent with the configuration determined for the genus by Woollam (1983) and Benson (1985). Two small anterior intercalary paraplates are present.
Comparison: Ctenidodinium fuscibasilarum most closely resembles C. ancorum (as discussed above). Ctenidodinium fuscibasilarum differs from all other species of Ctenidodinium by the characteristically larg, dark, thickened antapical paraplate with spinose parasutures. The Mid Jurassic species C. sellwoodii may closely resemble C. fuscibasilarum in general morphology aside from the dark 1’’’’ paraplate. Ctenidodinium sellwoodii is a variable form and can have few, irregularly inserted short parasutural processes like C. fuscibasilarum (see Woollam, 1983). Isolated, more spinose epicysts of C. fuscibasilarum may be difficult to distinguish from those of C. sellwoodii. Many other species of this genus have parasutures which are surmounted by regularly inserted and relatively dense processes and thus differ profoundly from Ctenidodinium fuscibasilarum. These comprise capitatum Wheeler & sarjeant 1990 ex Wheeler & Sarjeant 1992, C combazii Dupin 1968, C. complanatum Harding 1990, C. continuum Gocht, 1970, C. cornigerum (Valensi 1953) jan du dhêne et al., 1985, C. elegantulum Millioud 1969, C. ornatum (Eisenack 1935) Deflandre 1939, C? rotundum Dodekova 1975, C.? scissum McIntre & brideaux 1980, C. tenellum and C? Thulium (Davies 19832) Jan du chêne et al. 1986. Ctenidodinium coronatum Prauss 1989 is characterised by prominent, distally smooth parasutural crests. The Late Jurassic species Ctenidodinium chondrum Drugg 1978 and C.? schizoblatum (Norris 1965) Lentin & Williams 1973 exhibit low, smooth parasutural crests. The most common Mid Jurassic representatives of Ctenidodinium in northwest Europe are C. combazii, C. continuum, C. ornatum and C. sellwoodii (Woollam & Riding 1983). Ctenidodinium combazii has a small antapical paraplate and long, distally furcate processes (Riding et al., 1985, pl. 1). The parasutural crests of C. continuum and C. ornatum are relatively high and surmounted by densely-inserted denticles or processes lacking bifid terminations.
Holotype: Riding and Helby, 2001d, figs.4J-K.
Age: Mid-Late Callovian.
Original description (Riding and Helby, 2001d):
Derivation of name: From the Latin fuscus, meaning dark or swarthy and basilaris meaning at the base. This refers to the prominent dark, thickened antapical (1’’’’) paraplate.
Holotype and type locality: Figures 4J-K, CPC 35368, Undan-3 well, conventional core sample at 3057.00m.
Stratigraphical distribution: Ctenidodinium fuscibasilarum has been recorded from Middle to Upper Callivian starta of the Timor Sea region. It ranges from the Wanaea digitate Zone (7bi) to the middle Rignaudella aemula Zone (7aiiaii) (Foster, this volume; Helby and Partridge, in prep.).
A species of Ctenidodinium, which is elongate subhexagonal in dorsoventral outline and with or without a small apical protuberance. Autophragm thin, smooth to occasionally microscabrate axcept the antapical paraplate, which has significantly thicker and darker autophragm. Paratabulatio fully indicated by low parasutural ridges, which may be surmounted by short, solid, slender spines or denticles. The spines and/or denticles are sharply pointed or bifurcate. Gonal spines are consistently present on the antapical paraplate, which normally is also characteristic by closely inserted intergonal spines. Elsewhere on the cyst, particularly on paraplates of the precingular and postcingular series, spines are sparse, irregularly developed and/ or commonly absent.
Dimensions (µm; n=37): Min.(Mean)Max.
Length of cyst excl. spines: 61(73)86
Width of cyst body at paracingulum: 54(70)94
Width of antapical paraplate excl. spines: 19(33)44
Length of parasutural spines (mainly on 1’’’’): 3(7)16
The measured specimens are from conventional core samles in undan-3 well at 3048.00m and 3057.00m.
Comments: The most characteristic feature of Ctenidodinium fuscibasilarum is the relatively dark, thickened antapical (1’’’’) paraplate which is normally surrounded by spines or processes (Fig. 4). The preferential thickening of a single paraplate is extremely unusual among dinoflagellate cysts and was hitherto unknown in this genus. The spines are longer and more numerous closer to the antapex and the gonal spines around the 1’’’’ paraplate are longest. This lengthening is typical of Ctenidodinium and other gonyaulacalean genera. The spines/denticles other than around the 1’’’’ paraplate are irregular and short (up to 2µm-5µm, when present). The parasutural ridges are highest around the paracingulum (1-2µm) n=and lowest in the antapical area. Around the apical series, they may occasionally be discontinuous. The specie sis normally elongate , however the outline is somewhat variable and forms which are wider than long have been occasionally observed. Most forms have the paracingulum inserted equatorially, but in some forms the hypocyst is longer than the epicyst. The paratabulation pattern is consistent with the configuration determined for the genus by Woollam (1983) and Benson (1985). Two small anterior intercalary paraplates are present.
Comparison: Ctenidodinium fuscibasilarum most closely resembles C. ancorum (as discussed above). Ctenidodinium fuscibasilarum differs from all other species of Ctenidodinium by the characteristically larg, dark, thickened antapical paraplate with spinose parasutures. The Mid Jurassic species C. sellwoodii may closely resemble C. fuscibasilarum in general morphology aside from the dark 1’’’’ paraplate. Ctenidodinium sellwoodii is a variable form and can have few, irregularly inserted short parasutural processes like C. fuscibasilarum (see Woollam, 1983). Isolated, more spinose epicysts of C. fuscibasilarum may be difficult to distinguish from those of C. sellwoodii. Many other species of this genus have parasutures which are surmounted by regularly inserted and relatively dense processes and thus differ profoundly from Ctenidodinium fuscibasilarum. These comprise capitatum Wheeler & sarjeant 1990 ex Wheeler & Sarjeant 1992, C combazii Dupin 1968, C. complanatum Harding 1990, C. continuum Gocht, 1970, C. cornigerum (Valensi 1953) jan du dhêne et al., 1985, C. elegantulum Millioud 1969, C. ornatum (Eisenack 1935) Deflandre 1939, C? rotundum Dodekova 1975, C.? scissum McIntre & brideaux 1980, C. tenellum and C? Thulium (Davies 19832) Jan du chêne et al. 1986. Ctenidodinium coronatum Prauss 1989 is characterised by prominent, distally smooth parasutural crests. The Late Jurassic species Ctenidodinium chondrum Drugg 1978 and C.? schizoblatum (Norris 1965) Lentin & Williams 1973 exhibit low, smooth parasutural crests. The most common Mid Jurassic representatives of Ctenidodinium in northwest Europe are C. combazii, C. continuum, C. ornatum and C. sellwoodii (Woollam & Riding 1983). Ctenidodinium combazii has a small antapical paraplate and long, distally furcate processes (Riding et al., 1985, pl. 1). The parasutural crests of C. continuum and C. ornatum are relatively high and surmounted by densely-inserted denticles or processes lacking bifid terminations.