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Chaenosphaerula magnifica
Chaenosphaerula magnifica, Damassa, 1997, p.169,171,173, pl.1, figs.1-12; pl.2, figs.4-7; pl.3, figs.1-3,6-9; text-figs.6A-D,7A-D,8A-D,9A-D.
Holotype: Damassa, 1997, pl.1, figs.1-2; text-fig.6B.
Stratigraphic and geographic occurrence: Late Oligocene at DSDP Site 338; Voering Plateau, Norwegian Sea (see Table 1).
Age: Late Oligocene.
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Original description: [Damassa, 1997, p.169,171,173]:
Diagnosis:
Spheroidal cysts, consisting of parasutural framework only, indicating a sexiform gonyaulacoid tabulation. Ventral configuration modified S-type; apical-ventral plate contacts variable, li/lu (6"/1') or A/ai (4'/as) for the {A, lu, ai, li} quartet, A/li (4'/6") for the {6, A, ai, li} quartet. Hypocyst torsion neutral. Antapical configuration symmetrical to weakly asymmetrical. Archeopyle not present, as there is no wall material except for the parasutural framework. Parasutural framework may be incompletely developed in apical and sulcal regions.
Description:
Shape: Spheroidal when not deformed.
Wall structure: Cysts composed of parasutural framework only; intervening wall material is not present. Parasutural framework consists of a structure which is T-shaped in cross section, composed of an outer element parallel to what would have been the cyst surface and an inner element which is perpendicular to it (e.g. Plate II, 7).
Archeopyle: Not present in the usual sense.
Tabulation: Sexiform gonyaulacoid tabulation delineated by parasutural framework; ventral configuration modified S-type. The following paraplates are present: four apicals (A-C, lu or 1'-4'); six precingulars (2-6, li or 1"6"); six cingulars (au, b, c, d, e, fi or lc-6c); anterior sulcal ai (as) and posterior sulcal Z (ps) consistently developed; others in sulcal series (Ii, Im, fm or rs, Is, ras) variably developed; six postcingulars (Iu, II-VI or 1"-6"3 of which Iu (1"3 may be only partially delineated; one posterior intercalary (X or ps); one antapical (Y or 1"'). Preapicals P and Q are not clearly delineated and may not be present. Incidental or anterior intercalary plate (K) not obviously present in most specimens (Plate I, 9). Flagellar scar area not clearly delineated. Apical contacts variable: lu (1') and A (4') may both contact C (3'), leaving A (4") in a metasert configuration (Plate I, 8; Fig. 8C, Fig. 9C). Apical sutures not consistently developed. Apical-ventral plate contacts also variable: contacts involving the plate quartet {A, lu, ai, li} or {4', 1', as, 6"} may be either A/ai (4'/as) or li/lu (6"/1') (Figs. 6 and 7). The {6, A, ai, li} or {5", 4', as, 6"} quartet is nearly always in the A/li or 4'/6" configuration (Figs. 6 and 7). Kofoidian tabulation formula: ?pr, 4', ?la, 6", 6c, 5s, 6", lp, 1"".
Dimensions:
Size: Intermediate
60-80 μm.
Remarks:
Intraspecific variability of the configuration of the quartet {A, ai, li, lu} or {4', as, 6", 1'} also occurs in an undescribed species of Cribroperidinium (Damassa et al., 1990, figs. 4A, B). Interspecific variability of configuration of the same plate quartet is known in the genus Hystrichokolpoma Klumpp, 1953 (Damassa et al., 1988). For example, in the type species, H. cincture, the configuration is li/lu (6"/1'), while in H. torquatum and other species, the plates are in the A/ai (4'/as) configuration. The two configurations of this quartet are among the criteria used to differentiate Leptodinium Klement, 1960 and Spiniferella Stover and Hardenbol, 1993, which are in the li/lu (6"/1') configuration, from Impagidinium Stover and Evitt, 1978 and Spiniferites Mantell, 1850, which are in the A/ai (4'/as) configuration. Although most specimens of Chaenosphaerula magnifica exhibit the A/li (4'/6") configuration of the {6, A, ai, li} or {5", 4', as, 6"} quartet, the opposite configuration (6/ai or 5"/as) is present in rare individuals (Plate I, 11; Fig. 8B, Fig. 9B). Chaenosphaerula magnifica shows an unusual degree of intraspecific variability in developing both the A/ai (4'/as) and li/lu (6"/1') configurations of the {A, ai, li, lu} or {4', as, 6", 1'} quartet (PlateI, 3, 8, 10, 11; Fig. 7); the A/ai (4'/as) configuration is dominant among specimens observed; the lengths of the paraplate contacts involved are also variable.
Affinities:
Chaenosphaerula magnifica most closely resembles Evittosphaerula paratabulata in the development of a cyst in which only a parasutural framework is preserved. The two species differ in aspects of tabulation and framework structure as described here. The expression of the sulcal paraplate Ii (rs) and the first postcingular Iu(1"3 in an otherwise 'open' sulcal area is reminiscent of species of Impagidinium (Plate I, 1, 5). In contrast to E. paratabulata, the 'perpendicular' element of the parasutural framework is internal to the one which would be parallel to the cyst surface in C. magnifica. Although the implications of this structure are uncertain, the interior expression of morphological features and elements of tabulation are known to occur in several other fossil dinoflagellates (e.g. Fensome et al., 1993).
Holotype: Damassa, 1997, pl.1, figs.1-2; text-fig.6B.
Stratigraphic and geographic occurrence: Late Oligocene at DSDP Site 338; Voering Plateau, Norwegian Sea (see Table 1).
Age: Late Oligocene.
-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
Original description: [Damassa, 1997, p.169,171,173]:
Diagnosis:
Spheroidal cysts, consisting of parasutural framework only, indicating a sexiform gonyaulacoid tabulation. Ventral configuration modified S-type; apical-ventral plate contacts variable, li/lu (6"/1') or A/ai (4'/as) for the {A, lu, ai, li} quartet, A/li (4'/6") for the {6, A, ai, li} quartet. Hypocyst torsion neutral. Antapical configuration symmetrical to weakly asymmetrical. Archeopyle not present, as there is no wall material except for the parasutural framework. Parasutural framework may be incompletely developed in apical and sulcal regions.
Description:
Shape: Spheroidal when not deformed.
Wall structure: Cysts composed of parasutural framework only; intervening wall material is not present. Parasutural framework consists of a structure which is T-shaped in cross section, composed of an outer element parallel to what would have been the cyst surface and an inner element which is perpendicular to it (e.g. Plate II, 7).
Archeopyle: Not present in the usual sense.
Tabulation: Sexiform gonyaulacoid tabulation delineated by parasutural framework; ventral configuration modified S-type. The following paraplates are present: four apicals (A-C, lu or 1'-4'); six precingulars (2-6, li or 1"6"); six cingulars (au, b, c, d, e, fi or lc-6c); anterior sulcal ai (as) and posterior sulcal Z (ps) consistently developed; others in sulcal series (Ii, Im, fm or rs, Is, ras) variably developed; six postcingulars (Iu, II-VI or 1"-6"3 of which Iu (1"3 may be only partially delineated; one posterior intercalary (X or ps); one antapical (Y or 1"'). Preapicals P and Q are not clearly delineated and may not be present. Incidental or anterior intercalary plate (K) not obviously present in most specimens (Plate I, 9). Flagellar scar area not clearly delineated. Apical contacts variable: lu (1') and A (4') may both contact C (3'), leaving A (4") in a metasert configuration (Plate I, 8; Fig. 8C, Fig. 9C). Apical sutures not consistently developed. Apical-ventral plate contacts also variable: contacts involving the plate quartet {A, lu, ai, li} or {4', 1', as, 6"} may be either A/ai (4'/as) or li/lu (6"/1') (Figs. 6 and 7). The {6, A, ai, li} or {5", 4', as, 6"} quartet is nearly always in the A/li or 4'/6" configuration (Figs. 6 and 7). Kofoidian tabulation formula: ?pr, 4', ?la, 6", 6c, 5s, 6", lp, 1"".
Dimensions:
Size: Intermediate
60-80 μm.
Remarks:
Intraspecific variability of the configuration of the quartet {A, ai, li, lu} or {4', as, 6", 1'} also occurs in an undescribed species of Cribroperidinium (Damassa et al., 1990, figs. 4A, B). Interspecific variability of configuration of the same plate quartet is known in the genus Hystrichokolpoma Klumpp, 1953 (Damassa et al., 1988). For example, in the type species, H. cincture, the configuration is li/lu (6"/1'), while in H. torquatum and other species, the plates are in the A/ai (4'/as) configuration. The two configurations of this quartet are among the criteria used to differentiate Leptodinium Klement, 1960 and Spiniferella Stover and Hardenbol, 1993, which are in the li/lu (6"/1') configuration, from Impagidinium Stover and Evitt, 1978 and Spiniferites Mantell, 1850, which are in the A/ai (4'/as) configuration. Although most specimens of Chaenosphaerula magnifica exhibit the A/li (4'/6") configuration of the {6, A, ai, li} or {5", 4', as, 6"} quartet, the opposite configuration (6/ai or 5"/as) is present in rare individuals (Plate I, 11; Fig. 8B, Fig. 9B). Chaenosphaerula magnifica shows an unusual degree of intraspecific variability in developing both the A/ai (4'/as) and li/lu (6"/1') configurations of the {A, ai, li, lu} or {4', as, 6", 1'} quartet (PlateI, 3, 8, 10, 11; Fig. 7); the A/ai (4'/as) configuration is dominant among specimens observed; the lengths of the paraplate contacts involved are also variable.
Affinities:
Chaenosphaerula magnifica most closely resembles Evittosphaerula paratabulata in the development of a cyst in which only a parasutural framework is preserved. The two species differ in aspects of tabulation and framework structure as described here. The expression of the sulcal paraplate Ii (rs) and the first postcingular Iu(1"3 in an otherwise 'open' sulcal area is reminiscent of species of Impagidinium (Plate I, 1, 5). In contrast to E. paratabulata, the 'perpendicular' element of the parasutural framework is internal to the one which would be parallel to the cyst surface in C. magnifica. Although the implications of this structure are uncertain, the interior expression of morphological features and elements of tabulation are known to occur in several other fossil dinoflagellates (e.g. Fensome et al., 1993).