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Ambonosphaera staffinensis
Ambonosphaera staffinensis, (Gitmez, 1970), Poulsen and Riding, 1992; Emendation: Poulsen and Riding, 1992, p.26, as Ambonosphaera? staffinensis.
Originally Meiourogonyaulax, subsequently Lithodinia, thirdly Polygonifera, fourthly (and now) Ambonosphaera?, fifthly Lithodinia?. Williams et al. (1998, p.39) retained this species in Ambonosphaera?.
Questionable assignment: Poulsen and Riding (1992, p.26).
Taxonomic junior synonym: Senoniasphaera? frisia, according to Poulsen and Riding (1992, p.26); Hexagonifera (now Senoniasphaera) jurassica, according to Williams et al. (1993, p.32) - however, elsewhere in the same publication, Williams et al. (1993, p.56) retained Hexagonifera (now Senoniasphaera) jurassica.
Holotype: Gitmez, 1970, pl.3, fig.1, text-figs.20A-B
Locus typicus: Shale from 100 ft. above the second dolerite sill, Staifin Bay, Skye (SS 627), England
Stratum typicum: Early Kimmeridgian
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Original description as Meiourogonyaulax staffinensis: [Gitmez, 1970, p. 276-278]:
Diagnosis:
Meiourogonyaulax having a subspherical to elongate theca, lacking the apex in all specimens seen.
Tabulation: ?", ?0a, 6", 6c, 6""", 2p, 1pv and 1"""".
Crests are moderately high, slightly granulate with smooth distal edges.
Cingulum and sulcus are characteristically marked by deep furrows. The cingulum is slightly helicoid, laevorotatory, the sulcus broads towards the antapex.
The shell surface is densely granular, sometimes tuberculate.
Description:
A proximate cyst of subspherical to elongate outline, with a dome-shaped hypotract. Because of the densely granulate surface, determination of the tabulation was difficult. The apex, with all the apical plates, was always lost to form the apical archaeopyle. No intercalary plate was observed. Six precingular plates are present: plate 1" is the smallest of the precingular plates, the others being almost uniform of size.
Six postcingular plates are also present, plates 1""" and 2""" being reduced to accommodate posterior intercalary plates, 1p, 2p and 1pv; plate 6""" is much larger. The positions of the boundaries between the plates 3""" and 4""", and between the sulcus and plate 1pv, could not be confirmed. The antapex is occupied by a single plate 1"""".
The cingulum is broad, not less than one tenth of the shell length, being slightly laevorotatory spiral.
The sulcus is likewise broad, extending onto both epitract and hypotract, being much broader towards the posterior.
The shell surface is densely granular and sometimes coarsely tuberculate. The tubercles have a diameter of approximately 0.5-1 µm; they are scattered at random over the generally finely granulate surface.
The crests on the sutures are moderately high, smooth or slightly granulate and faintly striate.
Dimensions:
Holotype: overall length (apex lacking) 50 µm, breadth 55 µm; crests 3-8 µm high; cingulum c. 6 µm broad.
Range of the English specimens (7 specimens measured): overall length (apex lacking) 48-80 µm, breadth 50-78 µm;
French specimens (6 specimens measured): overall length (apex lacking) 65-75 µm, breadth 58-80 µm; Scottish samples (4 specimens measured): overall length (apex lacking) 50-60 µm, breadth 45-70 µm.
Affinities:
Specimens were observed in the assemblages from England, Scotland and France; they differ in the nature of the crests, surface ornamentation and general aspect from all previously described species of Meiourogonyaulax.
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Emended description:
Poulsen and Riding, 1992, p. 26:
Diagnosis:
Small, proximate, camocavate to circumcavate, dinoflagellate cysts with a subspherical, ovoidal to rounded subpentagonal ambitus. Wall layers attached laterally and/or dorsoventrally. Endocyst consistently subspherical, formed by relatively thick, scabrate to granulate endophragm. Periphragm thin and smooth, normally formed into a rounded antapical protuberance.
Gonyaulacacean paratabulation partially indicated.
Paracingulum consistently marked by low, smooth parasutural ridges on the periphragm. The remaining paraplate series may be delineated by complete or discontinuous parasutural ridges.
Kofoidian formula: ?pr, 4", 6", ?6c, ?6""", ?1p, ?1""""; sexiform gonyaulacacean configuration with a median, L-type parasulcus (Evitt, 1985). Archeopyle apical, type (4A), operculum free.
Description:
A small (42 to 51 µm in length) species, questionably attributed to Ambonosphaera, which is camocavate to circumcavate, proximate and strongly dorsoventrally compressed. The periphragm and endophragm are in contact laterally or the contact area may comprise the dorsal and ventral sides. The dorsoventral outline varies from subcircular to rounded subpentangular, largely depending on the development or prominence of the relatively short, rounded antapical protuberance formed by the thin, smooth periphragm. The endophragm, by contrast, is scabrate to granulate and relatively thick (up to 1.5 µm) the endocyst has a circular ambitus. Low, distally smooth ridges, formed by periphragm, partially indicate a sexiform gonyaulacacean paratabulation. The parasulcus is median and longitudinal (L-type of Evitt, 1985) and the Kofoidian formula is interpreted as being: ?pr, 4", 6", ?6c, ?6""", ?1p, ?1"""". The paracingulum is consistently marked, but is undivided; it is laevorotatory and displaced ventrally by up to its height, although the offset is commonly less than this. Remaining paraplate series may be partially delineated, the parasutural ridges are commonly discontinuous.
The principal archeopyle suture indicates the position of the parasulcus and the nature of the anterior and posterior sides of the precingular and apical paraplate series respectively (see Text-Figure 1). The archeopyle is apical, type (4A), apparently with a free operculum. No isolated operculae have been recovered.
Dimensions: Minimum (Mean) Maximum
Overall cyst length:42.0 (46.5) 51.0 µm (excluding operculum)
Overall cyst width:40.0 (44.5) 53.5 µm
Endocyst length:36.0 (42.5) 45.0 µm (excluding operculum)
Endocyst width:35.5 (43.5) 48.0 µm
Originally Meiourogonyaulax, subsequently Lithodinia, thirdly Polygonifera, fourthly (and now) Ambonosphaera?, fifthly Lithodinia?. Williams et al. (1998, p.39) retained this species in Ambonosphaera?.
Questionable assignment: Poulsen and Riding (1992, p.26).
Taxonomic junior synonym: Senoniasphaera? frisia, according to Poulsen and Riding (1992, p.26); Hexagonifera (now Senoniasphaera) jurassica, according to Williams et al. (1993, p.32) - however, elsewhere in the same publication, Williams et al. (1993, p.56) retained Hexagonifera (now Senoniasphaera) jurassica.
Holotype: Gitmez, 1970, pl.3, fig.1, text-figs.20A-B
Locus typicus: Shale from 100 ft. above the second dolerite sill, Staifin Bay, Skye (SS 627), England
Stratum typicum: Early Kimmeridgian
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Original description as Meiourogonyaulax staffinensis: [Gitmez, 1970, p. 276-278]:
Diagnosis:
Meiourogonyaulax having a subspherical to elongate theca, lacking the apex in all specimens seen.
Tabulation: ?", ?0a, 6", 6c, 6""", 2p, 1pv and 1"""".
Crests are moderately high, slightly granulate with smooth distal edges.
Cingulum and sulcus are characteristically marked by deep furrows. The cingulum is slightly helicoid, laevorotatory, the sulcus broads towards the antapex.
The shell surface is densely granular, sometimes tuberculate.
Description:
A proximate cyst of subspherical to elongate outline, with a dome-shaped hypotract. Because of the densely granulate surface, determination of the tabulation was difficult. The apex, with all the apical plates, was always lost to form the apical archaeopyle. No intercalary plate was observed. Six precingular plates are present: plate 1" is the smallest of the precingular plates, the others being almost uniform of size.
Six postcingular plates are also present, plates 1""" and 2""" being reduced to accommodate posterior intercalary plates, 1p, 2p and 1pv; plate 6""" is much larger. The positions of the boundaries between the plates 3""" and 4""", and between the sulcus and plate 1pv, could not be confirmed. The antapex is occupied by a single plate 1"""".
The cingulum is broad, not less than one tenth of the shell length, being slightly laevorotatory spiral.
The sulcus is likewise broad, extending onto both epitract and hypotract, being much broader towards the posterior.
The shell surface is densely granular and sometimes coarsely tuberculate. The tubercles have a diameter of approximately 0.5-1 µm; they are scattered at random over the generally finely granulate surface.
The crests on the sutures are moderately high, smooth or slightly granulate and faintly striate.
Dimensions:
Holotype: overall length (apex lacking) 50 µm, breadth 55 µm; crests 3-8 µm high; cingulum c. 6 µm broad.
Range of the English specimens (7 specimens measured): overall length (apex lacking) 48-80 µm, breadth 50-78 µm;
French specimens (6 specimens measured): overall length (apex lacking) 65-75 µm, breadth 58-80 µm; Scottish samples (4 specimens measured): overall length (apex lacking) 50-60 µm, breadth 45-70 µm.
Affinities:
Specimens were observed in the assemblages from England, Scotland and France; they differ in the nature of the crests, surface ornamentation and general aspect from all previously described species of Meiourogonyaulax.
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Emended description:
Poulsen and Riding, 1992, p. 26:
Diagnosis:
Small, proximate, camocavate to circumcavate, dinoflagellate cysts with a subspherical, ovoidal to rounded subpentagonal ambitus. Wall layers attached laterally and/or dorsoventrally. Endocyst consistently subspherical, formed by relatively thick, scabrate to granulate endophragm. Periphragm thin and smooth, normally formed into a rounded antapical protuberance.
Gonyaulacacean paratabulation partially indicated.
Paracingulum consistently marked by low, smooth parasutural ridges on the periphragm. The remaining paraplate series may be delineated by complete or discontinuous parasutural ridges.
Kofoidian formula: ?pr, 4", 6", ?6c, ?6""", ?1p, ?1""""; sexiform gonyaulacacean configuration with a median, L-type parasulcus (Evitt, 1985). Archeopyle apical, type (4A), operculum free.
Description:
A small (42 to 51 µm in length) species, questionably attributed to Ambonosphaera, which is camocavate to circumcavate, proximate and strongly dorsoventrally compressed. The periphragm and endophragm are in contact laterally or the contact area may comprise the dorsal and ventral sides. The dorsoventral outline varies from subcircular to rounded subpentangular, largely depending on the development or prominence of the relatively short, rounded antapical protuberance formed by the thin, smooth periphragm. The endophragm, by contrast, is scabrate to granulate and relatively thick (up to 1.5 µm) the endocyst has a circular ambitus. Low, distally smooth ridges, formed by periphragm, partially indicate a sexiform gonyaulacacean paratabulation. The parasulcus is median and longitudinal (L-type of Evitt, 1985) and the Kofoidian formula is interpreted as being: ?pr, 4", 6", ?6c, ?6""", ?1p, ?1"""". The paracingulum is consistently marked, but is undivided; it is laevorotatory and displaced ventrally by up to its height, although the offset is commonly less than this. Remaining paraplate series may be partially delineated, the parasutural ridges are commonly discontinuous.
The principal archeopyle suture indicates the position of the parasulcus and the nature of the anterior and posterior sides of the precingular and apical paraplate series respectively (see Text-Figure 1). The archeopyle is apical, type (4A), apparently with a free operculum. No isolated operculae have been recovered.
Dimensions: Minimum (Mean) Maximum
Overall cyst length:42.0 (46.5) 51.0 µm (excluding operculum)
Overall cyst width:40.0 (44.5) 53.5 µm
Endocyst length:36.0 (42.5) 45.0 µm (excluding operculum)
Endocyst width:35.5 (43.5) 48.0 µm