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Belowia balteus
Belowia balteus, Riding and Helby, 2001g, p.191,193,195, figs.5A-L,6A-F,7A-L.
NOW Belowicysta. Originally Belowia (generic name illegitimate), subsequently (and now) Belowicysta.
Holotype: Riding and Helby, 2001g, figs.6A-C. N.I.A.
Type locality: Lelinta Formation, Misool, eastern Indonesia
Stratigraphical distribution: Thitonian Cirbroperidinium perforans Zone (5d) to the Omatia montgomeryi Zone(5c) in the Timor Sea region (Foster, this volume; Helby & Partridge, in prep.); Tithonian lower part of the Lelinta Formation (Fageo Group) of Misool, eastern Indonesia.
Age: Tithonian.
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Original description: [Riding and Helby, 2001g]:
Description:
A species of Belowia with an ellipsoidal cyst body, that in polar view, is indented at the parasulcus. The autophragm is 1-1.5 µm thick and usually densely striate to occasionally rugulate, especially close to the postcingular processes. It may also be verrucate and irregularly and sparsely reticulate. The ectophragm is extremely variable in form, ranging from a sparse trabeculum, through a wide, complex trabeculum, to a thin (0.5µm), perforate wall.
Relatively short, solid, trabeculate processes consistently emerge from the vicinity of the anterior and posterior paracingular sutures. These form a projecting ectophragmal tunnel along the paracingulum, terminating at the relatively broad parasulcus. Close to the top of the postcingular paraplate series, a skirt-like ectophragmal structure is generally developed which extends antapically. This ectophragmal skirt may be supported by five intratabular postcingular processes representing paraplates 2"' to 6"', or by a variable number of nontabular processes. The processes are displaced toward the anterior margin of the paraplates. Where developed, the processes are extremely variable and may be slender, solid, wide or hollow and occasionally merge distally with the ectophragm. The ectophragmal skirt commonly terminates antapically in an open, solid girdle-like structure (Figs 5I, L), but this structure is sometimes absent (Fig. 7L).
The strongly indented parasulcus is frequently indicated by a low, smooth parasultural ridge.
The operculum is normally free, but specimens were observed where the operculum has fallen back into the autocyst.
Dimensions (µm, n=57): Min. (Mean) Max.
Maximum overall diameter: 83 (118) 159
Maximum lateral diameter of cyst body: 64 (91) 107
Maximum overall dorsoventral diameter: 80 (110) 151
Maximum dorsoventral diameter of cyst body: 63 (85) 105
Height of paracingular processes/trabeculum: 3 (8) 105
Height of postcingular processes/trabeculum: 8 (18) 35
The measured specimens are from ditch cuttings in Tenacious-1 ST1 well between 2975.00m and 2980m and outcrop material from the Thitonian Lelinta Formation (Fageo Group) of Misool, eastern Indonesia (Hasibuan, 1990; Helby & Hasibuan, 1988).
The 57 specimens in the above table comprise 37 of a larger morphotype 1 with distinct postcingular processes (Figs 5,6), 14 examples of the smaller morphotype 2, with a more continuous perforate extophragm (Fig. 7), and 6 intermediate forms. The dimensions of morphotypes 1 and 2 are set out below to document the size differences between these two end members of a continuously variable complex. The dimensions of the intermediate forms are not tabulated. The tables below principally illustrate the difference in the size of the ectophragm of the two morphotypes. Thus the maximum overall lateral and dorsoventral diameters are significantly different while other measurements are comparable.
Morphotype 1 (µm=37):
Maximum overall lateral diameter: 83 (124) 159
Maximum lateral diameter of cyst body: 64 (92) 107
Maximum overall dorsoventral diameter: 86 (116) 151
Maximum dorsoventral diameter of cyst body: 63 (85) 102
Height of paracingular processes/trabeculum: 3 (8) 19
Height of postcingular processes/trabeculum: 12 (19) 35
The above specimens are from Tenacious-1 ST1 well at 2975.00m-2980.00m and the Tithonian part of the Lelinta Formation of Misool, eastern Indonesia.
Morphotype 2 (µm, n=14):
Maximum overall lateral diameter: 91 (104) 130
Maximum lateral diameter of cyst body: 78 (89) 105
Maximum overall dorsoventral diameter: 80 (100) 118
Maximum dorsoventral diameter of cyst body: 66 (85) 105
Height of paracingular processes/trabeculum: 4 (8) 14
Height of postcingular processes/trabeculum: 8 (14) 29
The above specimens are all from sample 81FH11 in the Lelinta Formation of Misool, eastern Indonesia (Tithonian).
Remarks:
The morphology of the processes and the ectophragm are extremely variable. As indicated above, two morphotypes are recognised, both of which are mainly found as polar compressions. The relatively common morphotype 1 normally has intratabular postcingular processes which support a skirt-like ectophragmal trabeculum that is open antapically and terminates in a solid, girdle-like structure. The postcingular processes are located unusually high on the postcingular paraplate series. Because the ectophragm is made up of thin elements, it is prone to folding. Thus the size and polar outline of the ectocyst are somewhat variable. The relatively rare morphotype 2, lacks postcingular processes, the ectocoel is relatively narrow and the ectophragm is reticulate with lacunae of varying sizes. Most lacunae are relatively small (1-3µm), but some may be considerably larger. These two variants are not assigned to separate taxa because intermediate forms occur and all variants have the same stratigraphical range.
Affinities:
Belowia is currently a monotypic genus and thus the principal comparisons with other taxa are at the generic level (see above). Specimens of morphotype 1 of Belowia balteus and Belowia sp. A herein, however, resemble variants of Rigaudella aemula (Deflandre 1939) Below 1982. This similarity is confined to the postcingular paraplate series, where the intratabular processes are connected distally by narrow trabeculae (compare Below, 1982, figs. 22-34). The other paraplate series lack these, therefore the two forms can be readily distinguished.
NOW Belowicysta. Originally Belowia (generic name illegitimate), subsequently (and now) Belowicysta.
Holotype: Riding and Helby, 2001g, figs.6A-C. N.I.A.
Type locality: Lelinta Formation, Misool, eastern Indonesia
Stratigraphical distribution: Thitonian Cirbroperidinium perforans Zone (5d) to the Omatia montgomeryi Zone(5c) in the Timor Sea region (Foster, this volume; Helby & Partridge, in prep.); Tithonian lower part of the Lelinta Formation (Fageo Group) of Misool, eastern Indonesia.
Age: Tithonian.
-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
Original description: [Riding and Helby, 2001g]:
Description:
A species of Belowia with an ellipsoidal cyst body, that in polar view, is indented at the parasulcus. The autophragm is 1-1.5 µm thick and usually densely striate to occasionally rugulate, especially close to the postcingular processes. It may also be verrucate and irregularly and sparsely reticulate. The ectophragm is extremely variable in form, ranging from a sparse trabeculum, through a wide, complex trabeculum, to a thin (0.5µm), perforate wall.
Relatively short, solid, trabeculate processes consistently emerge from the vicinity of the anterior and posterior paracingular sutures. These form a projecting ectophragmal tunnel along the paracingulum, terminating at the relatively broad parasulcus. Close to the top of the postcingular paraplate series, a skirt-like ectophragmal structure is generally developed which extends antapically. This ectophragmal skirt may be supported by five intratabular postcingular processes representing paraplates 2"' to 6"', or by a variable number of nontabular processes. The processes are displaced toward the anterior margin of the paraplates. Where developed, the processes are extremely variable and may be slender, solid, wide or hollow and occasionally merge distally with the ectophragm. The ectophragmal skirt commonly terminates antapically in an open, solid girdle-like structure (Figs 5I, L), but this structure is sometimes absent (Fig. 7L).
The strongly indented parasulcus is frequently indicated by a low, smooth parasultural ridge.
The operculum is normally free, but specimens were observed where the operculum has fallen back into the autocyst.
Dimensions (µm, n=57): Min. (Mean) Max.
Maximum overall diameter: 83 (118) 159
Maximum lateral diameter of cyst body: 64 (91) 107
Maximum overall dorsoventral diameter: 80 (110) 151
Maximum dorsoventral diameter of cyst body: 63 (85) 105
Height of paracingular processes/trabeculum: 3 (8) 105
Height of postcingular processes/trabeculum: 8 (18) 35
The measured specimens are from ditch cuttings in Tenacious-1 ST1 well between 2975.00m and 2980m and outcrop material from the Thitonian Lelinta Formation (Fageo Group) of Misool, eastern Indonesia (Hasibuan, 1990; Helby & Hasibuan, 1988).
The 57 specimens in the above table comprise 37 of a larger morphotype 1 with distinct postcingular processes (Figs 5,6), 14 examples of the smaller morphotype 2, with a more continuous perforate extophragm (Fig. 7), and 6 intermediate forms. The dimensions of morphotypes 1 and 2 are set out below to document the size differences between these two end members of a continuously variable complex. The dimensions of the intermediate forms are not tabulated. The tables below principally illustrate the difference in the size of the ectophragm of the two morphotypes. Thus the maximum overall lateral and dorsoventral diameters are significantly different while other measurements are comparable.
Morphotype 1 (µm=37):
Maximum overall lateral diameter: 83 (124) 159
Maximum lateral diameter of cyst body: 64 (92) 107
Maximum overall dorsoventral diameter: 86 (116) 151
Maximum dorsoventral diameter of cyst body: 63 (85) 102
Height of paracingular processes/trabeculum: 3 (8) 19
Height of postcingular processes/trabeculum: 12 (19) 35
The above specimens are from Tenacious-1 ST1 well at 2975.00m-2980.00m and the Tithonian part of the Lelinta Formation of Misool, eastern Indonesia.
Morphotype 2 (µm, n=14):
Maximum overall lateral diameter: 91 (104) 130
Maximum lateral diameter of cyst body: 78 (89) 105
Maximum overall dorsoventral diameter: 80 (100) 118
Maximum dorsoventral diameter of cyst body: 66 (85) 105
Height of paracingular processes/trabeculum: 4 (8) 14
Height of postcingular processes/trabeculum: 8 (14) 29
The above specimens are all from sample 81FH11 in the Lelinta Formation of Misool, eastern Indonesia (Tithonian).
Remarks:
The morphology of the processes and the ectophragm are extremely variable. As indicated above, two morphotypes are recognised, both of which are mainly found as polar compressions. The relatively common morphotype 1 normally has intratabular postcingular processes which support a skirt-like ectophragmal trabeculum that is open antapically and terminates in a solid, girdle-like structure. The postcingular processes are located unusually high on the postcingular paraplate series. Because the ectophragm is made up of thin elements, it is prone to folding. Thus the size and polar outline of the ectocyst are somewhat variable. The relatively rare morphotype 2, lacks postcingular processes, the ectocoel is relatively narrow and the ectophragm is reticulate with lacunae of varying sizes. Most lacunae are relatively small (1-3µm), but some may be considerably larger. These two variants are not assigned to separate taxa because intermediate forms occur and all variants have the same stratigraphical range.
Affinities:
Belowia is currently a monotypic genus and thus the principal comparisons with other taxa are at the generic level (see above). Specimens of morphotype 1 of Belowia balteus and Belowia sp. A herein, however, resemble variants of Rigaudella aemula (Deflandre 1939) Below 1982. This similarity is confined to the postcingular paraplate series, where the intratabular processes are connected distally by narrow trabeculae (compare Below, 1982, figs. 22-34). The other paraplate series lack these, therefore the two forms can be readily distinguished.