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Rhynchodiniopsis crassicornuta
Rhynchidiniopsis crassicornuta (Klement, 1960, p.38–39, pl.5, figs.1–3) Below, 1981a, p.118. Emendation: Sarjeant, 1984a, p.158–160, as Rhynchodiniopsis crassicornuta.
Now Gonyaulacysta?. Originally Gonyaulax, subsequently Gonyaulacysta, thirdly (and now) Gonyaulacysta?, fourthly Rhynchodiniopsis. Lentin and Williams, 1981 questionably retained this species in Gonyaulacysta Deflandre, 1964; however, Sarjeant, 1982 emended the diagnosis of Rhynchodiniopsis and retained the species in this genus. Jan du Chêne et al., 1986 questionably retained the species in Gonyaulacysta.
Holotype: Klement, 1960, pl., pl.5, fig.1; Sarjeant, 1984, pl.2, figs.1-2, text-fig.2; Jan du Chêne et al., 1986, pl.45, figs.1-4
Paratypes: Klement, 1960
Locus typicus: Scherstetten 1 borehole, southwest Germany, at between 1715.2 and 1716.8 m. depth
Stratum typicum: Kimmeridgian
Emended diagnosis: Sarjeant, 1984, p.158-159
Cyst proximate to proximochorate, monocornucavate to almost epicavate; minor separation of wall layers laterally at the level of the cingulum may also occur, but the circumcavate condition is not approached. Ambitus ovoidal to broadly ellipsoidal; epitract and hypotract of comparable size and shape. Apical horn strong and broad, blunt-tipped. Parasutures marked by low to moderately high crests bearing well-spaced spinelets, capitate, bifurcate or trifurcate. Paratabulation 2pr, ?3, 4", ?0a, 6", 7c, 6""", 2p, 0pv, 1"""", 4s. Cingulum of moderate width, strongly laevorotatory, its two ends differing in anteroposterior position by roughly twice its width; the seventh cingular (7c) is small and quadrate. Sulcus narrow, widening slightly in its midventral section and divided into four paraplates - an elongate anterior sulcal, two median sulcals (the more anterior almost quadrate, the more posterior of irregular shape) and an elongate posterior sulcal, somewhat broader than the anterior sulcal. Paraplate 4" is of relatively small size and quadrate shape, though narrowing anteriorly; it has a broad boundary with 6". The parasuture separating these two paraplates intersects 1" in a position markedly anterior to the junction of the latter paraplate with the sulcus. The small first postcingular (1""") is separated from the antapex by a posterior intercalary paraplate (1p) similar in size and shape to the posterior sulcal. The sixth postcingular (6""") is transversely flattened and divided from the antapex by an almost quadrate posterior intercalary (2p). The antapical paraplate (1"""") is relatively small. Archaeopyle single-plate precingular, Type P (3" only); operculum free.
Dimensions: Holotype; overall length 101 µm, length of horn 22 µm, overall breadth 66 µm, maximum height of crests (including spines) 8 µm. Range of dimensions; overall length 78-112 µm (mean 104 µm), overall breadth 52-69 µm (mean 70 µm), length of horn 17-29 µm (mean 20 µm).
Description: Sarjeant, 1984, p.159-160
The apical horn is broad-based, with concave flanks; so broad-based, indeed, that the cysts may be equally well termed cornucavate or epicavate. The blunt tip of the apical horn is occupied by the first preapical paraplate (1pr), while the second (2pr) occupies the right flank of the anterior portion of the horn. A third preapical appears also to be developed in a corresponding position on the ventral surface of the horn tip, but this is so unusual a feature that I prefer to include it only tentatively into my drawing (as ?3pr). If it is indeed present, then the first apical (1") is unusually short and does not reach the horn tip.
In part because of the relatively small size of paraplate 4", in part because the cyst is relatively elongate, the sixth postcingular (6") is quite large, comparable in size to the first (1"). 3" is the largest of the precingulars and 4""" the largest of all the paraplates. The first, second and sixth postcingulars are all reduced; the first two are both separated from the antapex by a posterior intercalary (1p).
The parasutural crests are uniformly acanthate, though the spacing of the spinelets and the relative height of crests and spinelets is variable, reaching a maximum around the antapex. The surface of the phragma is granulate, with granules of variable size and density according to position on the cyst.
Remarks: In the style of its horn and the nature of its sutural crests, this species approaches the morphology of the genera Hystrichogonyaulax and Gonyaulacysta. Because of the shape of its fourth apical paraplate (less elongate than in Gonyaulacysta and with a broader boundary with 6") and because uncertainties concerning the nature of the archaeopyle in Hystrichogonyaulax (see Sarjeant, 1982, p. 126) incline me presently to avoid using that generic name, its placement into Rhynchodiniopsis is preferred. The detail of its ventral paratabulation and the nature of its crests differentiate R. crassicornuta from all other species described to date.
The most similar species is perhaps the Late Oxfordian to lowest Kimmeridgian Meristaulax granulosa (Gitmez, 1970) Sarjeant and Gocht; however, the latter is distinguished by its more densely acanthate crests, by having lines of spines marking accessory crests and by its broader and less pronouncedly helicoid cingulum.
Because the detail of its paratabulation was left vague in the original description, the recognition of this species has presented considerable difficulties hitherto. The western Canadian specimens attributed to it by Pocock (1972) were not illustrated and his identification cannot, therefore, be confirmed.
Now Gonyaulacysta?. Originally Gonyaulax, subsequently Gonyaulacysta, thirdly (and now) Gonyaulacysta?, fourthly Rhynchodiniopsis. Lentin and Williams, 1981 questionably retained this species in Gonyaulacysta Deflandre, 1964; however, Sarjeant, 1982 emended the diagnosis of Rhynchodiniopsis and retained the species in this genus. Jan du Chêne et al., 1986 questionably retained the species in Gonyaulacysta.
Holotype: Klement, 1960, pl., pl.5, fig.1; Sarjeant, 1984, pl.2, figs.1-2, text-fig.2; Jan du Chêne et al., 1986, pl.45, figs.1-4
Paratypes: Klement, 1960
Locus typicus: Scherstetten 1 borehole, southwest Germany, at between 1715.2 and 1716.8 m. depth
Stratum typicum: Kimmeridgian
Emended diagnosis: Sarjeant, 1984, p.158-159
Cyst proximate to proximochorate, monocornucavate to almost epicavate; minor separation of wall layers laterally at the level of the cingulum may also occur, but the circumcavate condition is not approached. Ambitus ovoidal to broadly ellipsoidal; epitract and hypotract of comparable size and shape. Apical horn strong and broad, blunt-tipped. Parasutures marked by low to moderately high crests bearing well-spaced spinelets, capitate, bifurcate or trifurcate. Paratabulation 2pr, ?3, 4", ?0a, 6", 7c, 6""", 2p, 0pv, 1"""", 4s. Cingulum of moderate width, strongly laevorotatory, its two ends differing in anteroposterior position by roughly twice its width; the seventh cingular (7c) is small and quadrate. Sulcus narrow, widening slightly in its midventral section and divided into four paraplates - an elongate anterior sulcal, two median sulcals (the more anterior almost quadrate, the more posterior of irregular shape) and an elongate posterior sulcal, somewhat broader than the anterior sulcal. Paraplate 4" is of relatively small size and quadrate shape, though narrowing anteriorly; it has a broad boundary with 6". The parasuture separating these two paraplates intersects 1" in a position markedly anterior to the junction of the latter paraplate with the sulcus. The small first postcingular (1""") is separated from the antapex by a posterior intercalary paraplate (1p) similar in size and shape to the posterior sulcal. The sixth postcingular (6""") is transversely flattened and divided from the antapex by an almost quadrate posterior intercalary (2p). The antapical paraplate (1"""") is relatively small. Archaeopyle single-plate precingular, Type P (3" only); operculum free.
Dimensions: Holotype; overall length 101 µm, length of horn 22 µm, overall breadth 66 µm, maximum height of crests (including spines) 8 µm. Range of dimensions; overall length 78-112 µm (mean 104 µm), overall breadth 52-69 µm (mean 70 µm), length of horn 17-29 µm (mean 20 µm).
Description: Sarjeant, 1984, p.159-160
The apical horn is broad-based, with concave flanks; so broad-based, indeed, that the cysts may be equally well termed cornucavate or epicavate. The blunt tip of the apical horn is occupied by the first preapical paraplate (1pr), while the second (2pr) occupies the right flank of the anterior portion of the horn. A third preapical appears also to be developed in a corresponding position on the ventral surface of the horn tip, but this is so unusual a feature that I prefer to include it only tentatively into my drawing (as ?3pr). If it is indeed present, then the first apical (1") is unusually short and does not reach the horn tip.
In part because of the relatively small size of paraplate 4", in part because the cyst is relatively elongate, the sixth postcingular (6") is quite large, comparable in size to the first (1"). 3" is the largest of the precingulars and 4""" the largest of all the paraplates. The first, second and sixth postcingulars are all reduced; the first two are both separated from the antapex by a posterior intercalary (1p).
The parasutural crests are uniformly acanthate, though the spacing of the spinelets and the relative height of crests and spinelets is variable, reaching a maximum around the antapex. The surface of the phragma is granulate, with granules of variable size and density according to position on the cyst.
Remarks: In the style of its horn and the nature of its sutural crests, this species approaches the morphology of the genera Hystrichogonyaulax and Gonyaulacysta. Because of the shape of its fourth apical paraplate (less elongate than in Gonyaulacysta and with a broader boundary with 6") and because uncertainties concerning the nature of the archaeopyle in Hystrichogonyaulax (see Sarjeant, 1982, p. 126) incline me presently to avoid using that generic name, its placement into Rhynchodiniopsis is preferred. The detail of its ventral paratabulation and the nature of its crests differentiate R. crassicornuta from all other species described to date.
The most similar species is perhaps the Late Oxfordian to lowest Kimmeridgian Meristaulax granulosa (Gitmez, 1970) Sarjeant and Gocht; however, the latter is distinguished by its more densely acanthate crests, by having lines of spines marking accessory crests and by its broader and less pronouncedly helicoid cingulum.
Because the detail of its paratabulation was left vague in the original description, the recognition of this species has presented considerable difficulties hitherto. The western Canadian specimens attributed to it by Pocock (1972) were not illustrated and his identification cannot, therefore, be confirmed.