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Ctenidodinium ancora
Ctenidodinium ancora Riding and Helby, 2001d, p.69,71, figs.3A-L.
The epithet is avowedly based on the Latin noun ancora (anchor) and thus should be cited as "ancora", not "ancorum" as indicated in Riding and Helby. N.I.A.
Holotype: Riding and Helby, 2001d, figs.3G, J.
Age: latest Bathonian-Callovian.
Derivation of the name: After the Latin ancora, meaning anchor and referring to the typically anchor-like process terminations.
Holotype and type locality: Figures 3G, J, CPC 35355, Rowan-1ST well, sidewall core sample at 3183.00m.
Statigraphical distribution: Ctenidodinium ancorum has been recorded from the uppermost Bathonian to the Callovian of the Timor Sea area, ranging from the upper Wannaea verrucosa Zone (7ciai) to the Rigaudella aemula Zone (7ai) (Foster, this volume; Helby & Partridge, in prep.)
Original description (Riding and Helby, 2001d):
A species of Ctenidodonium subhexagonal in dorsoventral outline, lacking an apical protuberance or horn. Autophragm thin, smooth to microscrabate and irregularly microreticulate. The antapical paraplate may have a thicker and thus marginally darker autophragm. Paratabulation fully indicated by parasutural ridges, which are regularly surmounted by processes. The processes are consistently solid, but otherwise are variable in form, being acuminate, bifid, conical/subconical or slender; distal terminations are bifurcate, blunt or sharp. Typically many processes are bifurcate with recurved terminations. At the distal end of the processes, immediately below the bifid tip there is a characteristic narrow, neck-like constriction which constitutes a natural breakpoint. Individual specimens may exhibit processes of varying morphologies. The longest processes are those in gonal positions around the antapical paraplate. Dark, subcircular accumulation bodies may be present.
Dimensions: (µm, n=38): Min.(Mean)Max.
Length of cyst excl. spines: 57(73)86
Length of epicyst excl. spines: 16(28)40
Length of hypocyst excl. spoines: 36(53)66
Width of cyst excl. spines: 57(77)106
Length of spines: 2(5)10
Height of parasutural ridges: 1(2)4
The measured speciemens are from conventional core samples from Undan-1 and Undan-4 well at 2996.15m and 3135.24m, respectively and sidewall core samples from mChallis-11 ST1 well at 1552.50m and Rowan-1ST well at 3183.0m
Comments: The most characteristic feature in Ctenidodinium ancorum are the processes which surround the parasutural ridges. Typically, the distal terminations are bifurcate, with recurved furcae (Fig. 3J). The processes may be bent distally at the tips so that they and the processes shafts may be at different focal levels at high magnifications. Trifid tips ion the gonal processes, or elsewhere, were not observed. These grapnel or anchor shaped process endings are reminiscent of the glochidia in the microspore massulae of the Late Cretaceous to Holocene water fern genus Azolla sensu lato (see Collinson, 1980). It is possible that these hooked processes evolved in order that this cyst species could attach itself to other individuals or to other sedimentary particles. The ornamentation elements, which have blunt or sharp terminations, may represent processes which have been damaged, the bifid tips breaking off during sedimentation and/or processing. This seems likely as the ‘necks’ of the processes, immediately below the recurved bifid tips are extremely slender (Fig. 3J). Furthermore, individual specimens have both bifid and sharp processes, thereby supporting the contention that the process terminations may be randomly damaged. Isolated tips were not seen in the residues, being close to the limit of optical resolution and also possibly removed by sieving during processing. The processes are longest around the antapex, being 5 µm and above (Fig. 3C). they become progressively shorter in an apical direction, typically ebing around 4 µm and 3 µm in the postcingular and paracingular series respectively. The species is relatively variable in size (see dimensions, above); this factor is probably due to the variable compressions and preservational style.
Comparison: Ctenidodinium ancorum most closely resembles Ctenidodinium fuscibasilarum sp. Nov., both having thicker and darker 1’’’’ paraplates, although in the latter the development is more extreme. In addition, C. ancorum has bifid processes surmounting the parasutural ridges over the entire cyst. Ctenidodinium aff. Tenellum Deflandre 1939, particularly, “Form B”, of Gocht (1970, pl. 42, figs. 7-8, Pl. 32, figs. 18a, b) is the European form most similar to C. ancorum in process distribution and style, bt is substantially smaller, has a conical epicyst, and appears to lack the thickening of the 1’’’’ paraplate. The Mid Jurassic C. sellwoodii (Sarjeant, 1975) Stover and Evitt 1978 may closely resemble C. ancorum is general morphology apart from the bifid process tips. The most common Mid Jurassic representatives of the genus in northwest Europe are C. combazii, C. continuum, C. ornatum abd C. sellwoodii (Woollam & Riding, 1983). Ctenidodinium combazii has a small antapical paraplate and long, distally elaborate 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 tip furcation. If observation of C. ancorum are gathered using low power objectives the bifid nature of the processes may not be apparent. In these cases the forms would possibly be identified as C. sellwoodii or C. tenellum.
The epithet is avowedly based on the Latin noun ancora (anchor) and thus should be cited as "ancora", not "ancorum" as indicated in Riding and Helby. N.I.A.
Holotype: Riding and Helby, 2001d, figs.3G, J.
Age: latest Bathonian-Callovian.
Derivation of the name: After the Latin ancora, meaning anchor and referring to the typically anchor-like process terminations.
Holotype and type locality: Figures 3G, J, CPC 35355, Rowan-1ST well, sidewall core sample at 3183.00m.
Statigraphical distribution: Ctenidodinium ancorum has been recorded from the uppermost Bathonian to the Callovian of the Timor Sea area, ranging from the upper Wannaea verrucosa Zone (7ciai) to the Rigaudella aemula Zone (7ai) (Foster, this volume; Helby & Partridge, in prep.)
Original description (Riding and Helby, 2001d):
A species of Ctenidodonium subhexagonal in dorsoventral outline, lacking an apical protuberance or horn. Autophragm thin, smooth to microscrabate and irregularly microreticulate. The antapical paraplate may have a thicker and thus marginally darker autophragm. Paratabulation fully indicated by parasutural ridges, which are regularly surmounted by processes. The processes are consistently solid, but otherwise are variable in form, being acuminate, bifid, conical/subconical or slender; distal terminations are bifurcate, blunt or sharp. Typically many processes are bifurcate with recurved terminations. At the distal end of the processes, immediately below the bifid tip there is a characteristic narrow, neck-like constriction which constitutes a natural breakpoint. Individual specimens may exhibit processes of varying morphologies. The longest processes are those in gonal positions around the antapical paraplate. Dark, subcircular accumulation bodies may be present.
Dimensions: (µm, n=38): Min.(Mean)Max.
Length of cyst excl. spines: 57(73)86
Length of epicyst excl. spines: 16(28)40
Length of hypocyst excl. spoines: 36(53)66
Width of cyst excl. spines: 57(77)106
Length of spines: 2(5)10
Height of parasutural ridges: 1(2)4
The measured speciemens are from conventional core samples from Undan-1 and Undan-4 well at 2996.15m and 3135.24m, respectively and sidewall core samples from mChallis-11 ST1 well at 1552.50m and Rowan-1ST well at 3183.0m
Comments: The most characteristic feature in Ctenidodinium ancorum are the processes which surround the parasutural ridges. Typically, the distal terminations are bifurcate, with recurved furcae (Fig. 3J). The processes may be bent distally at the tips so that they and the processes shafts may be at different focal levels at high magnifications. Trifid tips ion the gonal processes, or elsewhere, were not observed. These grapnel or anchor shaped process endings are reminiscent of the glochidia in the microspore massulae of the Late Cretaceous to Holocene water fern genus Azolla sensu lato (see Collinson, 1980). It is possible that these hooked processes evolved in order that this cyst species could attach itself to other individuals or to other sedimentary particles. The ornamentation elements, which have blunt or sharp terminations, may represent processes which have been damaged, the bifid tips breaking off during sedimentation and/or processing. This seems likely as the ‘necks’ of the processes, immediately below the recurved bifid tips are extremely slender (Fig. 3J). Furthermore, individual specimens have both bifid and sharp processes, thereby supporting the contention that the process terminations may be randomly damaged. Isolated tips were not seen in the residues, being close to the limit of optical resolution and also possibly removed by sieving during processing. The processes are longest around the antapex, being 5 µm and above (Fig. 3C). they become progressively shorter in an apical direction, typically ebing around 4 µm and 3 µm in the postcingular and paracingular series respectively. The species is relatively variable in size (see dimensions, above); this factor is probably due to the variable compressions and preservational style.
Comparison: Ctenidodinium ancorum most closely resembles Ctenidodinium fuscibasilarum sp. Nov., both having thicker and darker 1’’’’ paraplates, although in the latter the development is more extreme. In addition, C. ancorum has bifid processes surmounting the parasutural ridges over the entire cyst. Ctenidodinium aff. Tenellum Deflandre 1939, particularly, “Form B”, of Gocht (1970, pl. 42, figs. 7-8, Pl. 32, figs. 18a, b) is the European form most similar to C. ancorum in process distribution and style, bt is substantially smaller, has a conical epicyst, and appears to lack the thickening of the 1’’’’ paraplate. The Mid Jurassic C. sellwoodii (Sarjeant, 1975) Stover and Evitt 1978 may closely resemble C. ancorum is general morphology apart from the bifid process tips. The most common Mid Jurassic representatives of the genus in northwest Europe are C. combazii, C. continuum, C. ornatum abd C. sellwoodii (Woollam & Riding, 1983). Ctenidodinium combazii has a small antapical paraplate and long, distally elaborate 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 tip furcation. If observation of C. ancorum are gathered using low power objectives the bifid nature of the processes may not be apparent. In these cases the forms would possibly be identified as C. sellwoodii or C. tenellum.