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Bourkidinium elegans
Bourkidinium elegans, Torricelli, 1997, p. 343,345, pl.2, figs.1-9.
Holotype: Torricelli, 1997, pl.2, fig.4.
Paratype: Torricelli, 1997, Plate 2, fig. 7
Type locality: Vallone Rosmarino Section, Sicily, Italy.
Type stratum: Monte Soro Flysch.
Stratigraphic occurrence: Early Hauterivian, Early Cretaceous of Sicily.
Age: early Hauterivian.
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Original description: [Torricelli, 1997]:
Diagnosis:
A Bourkidinium with elongate ellipsoidal cysts, a smooth autophragm and long tubular processes generally confined to the apical and antapical paraplate series. Occasionally, a process may be present in the precingular region.
Description:
Medium-sized skolochorate cyst, elongate ellipsoidal in shape, with rounded apex and antapex.
Autophragm thin and smooth.
Long, hollow, tubular processes occur and are generally confined to the polar extremities of the cyst. In one specimen a single process has been observed on the precingular paraplate series (Plate II, 7). There are usually four apical processes and four antapical processes. Occasionally, five antapical processes have been observed (Plate II, 8). When fewer than four antapical processes are present, circular scars on the cyst body demonstrate that missing processes have been broken off (Plate II, 3). Distal tips of processes open and flared, serrate or simple.
Archeopyle apical, type (tA), operculum free. Principal archeopyle suture exhibiting a marked sulcal notch and short but distinct accessory sutures, possibly indicating six precingular paraplates (Plate II, 9).
Dimensions:
Holotype (without operculum): central body length=43 μm; width=23 μm; processes length=22-23 μm.
Range: central body length = 34-45 μm; width = 23-28 μm; processes length = 19-27 μm; 9 specimens measured.
Affinities/Comparisons:
Bourkidinium elegans differs from Bourkidinium granulatum Morgan, 1975 in possessing a smooth autophragm, and from Bourkidinium psilatum Singh, 1983 in possessing usually four apical and four antapical processes with distal tips open and flared, instead of five to seven processes at each end of the cyst terminating distally in long recurved spines.
Stratigraphic remarks:
In the present study Bourkidinium elegans and Muderongia siciliana have not been found in the same assemblage, the former being observed in a stratigraphic position higher than the latter. According to calcareous nannoplankton data (F. Lottaroli, pers. commun., 1995), both the samples containing Bourkidinium elegans and those containing Muderongia siciliana are characterized by the concurrent presence of nannofossils Nannoconus bucheri Broennimann and Cruciellipsis cuvillieri (Manivit) Thierstein, while Lithraphidites bollii Thierstein is absent. According to Channell et al. (1995), this nannoplankton assemblage constrains the chronostratigraphic attribution of the studied samples to the lower Hauterivian.
Holotype: Torricelli, 1997, pl.2, fig.4.
Paratype: Torricelli, 1997, Plate 2, fig. 7
Type locality: Vallone Rosmarino Section, Sicily, Italy.
Type stratum: Monte Soro Flysch.
Stratigraphic occurrence: Early Hauterivian, Early Cretaceous of Sicily.
Age: early Hauterivian.
-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
Original description: [Torricelli, 1997]:
Diagnosis:
A Bourkidinium with elongate ellipsoidal cysts, a smooth autophragm and long tubular processes generally confined to the apical and antapical paraplate series. Occasionally, a process may be present in the precingular region.
Description:
Medium-sized skolochorate cyst, elongate ellipsoidal in shape, with rounded apex and antapex.
Autophragm thin and smooth.
Long, hollow, tubular processes occur and are generally confined to the polar extremities of the cyst. In one specimen a single process has been observed on the precingular paraplate series (Plate II, 7). There are usually four apical processes and four antapical processes. Occasionally, five antapical processes have been observed (Plate II, 8). When fewer than four antapical processes are present, circular scars on the cyst body demonstrate that missing processes have been broken off (Plate II, 3). Distal tips of processes open and flared, serrate or simple.
Archeopyle apical, type (tA), operculum free. Principal archeopyle suture exhibiting a marked sulcal notch and short but distinct accessory sutures, possibly indicating six precingular paraplates (Plate II, 9).
Dimensions:
Holotype (without operculum): central body length=43 μm; width=23 μm; processes length=22-23 μm.
Range: central body length = 34-45 μm; width = 23-28 μm; processes length = 19-27 μm; 9 specimens measured.
Affinities/Comparisons:
Bourkidinium elegans differs from Bourkidinium granulatum Morgan, 1975 in possessing a smooth autophragm, and from Bourkidinium psilatum Singh, 1983 in possessing usually four apical and four antapical processes with distal tips open and flared, instead of five to seven processes at each end of the cyst terminating distally in long recurved spines.
Stratigraphic remarks:
In the present study Bourkidinium elegans and Muderongia siciliana have not been found in the same assemblage, the former being observed in a stratigraphic position higher than the latter. According to calcareous nannoplankton data (F. Lottaroli, pers. commun., 1995), both the samples containing Bourkidinium elegans and those containing Muderongia siciliana are characterized by the concurrent presence of nannofossils Nannoconus bucheri Broennimann and Cruciellipsis cuvillieri (Manivit) Thierstein, while Lithraphidites bollii Thierstein is absent. According to Channell et al. (1995), this nannoplankton assemblage constrains the chronostratigraphic attribution of the studied samples to the lower Hauterivian.