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Leptodinium ancoralium
Leptodinium ancoralium Mantle, 2005, p.256,258–260, pl.3,figs.1–9; text-figs.7A–D,8A–C.
Questionable assignment: Mantle (2005, p.256).
Holotype: Mantle, 2005, pl.3, figs.4–7.
Age: Callovian–early Oxfordian.
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Original description (Mantle, 2005):
Leptodinium? ancoralium sp. nov. (Plate III, 1–9; Figs. 7A–D, 8A–C).
Holotype and type locality: Challis-11 ST1 well, sidewall core sample at 1552.50 m, Slide no. 3, EF N27/1. CPC no. 38827 (Plate III, 4–7).
Etymology: Latin, ancoralis; with reference to the anchor-shaped processes surmounting the parasutural crests.
Diagnosis: Cysts subspherical, ovoidal, or polyhedral, proximochorate, typically cornucavate, medium-sized with a circular cingular cross-section. Gonyaulacacean paratabulation indicated by parasutural septa surmounted by bifurcating, anchor-like spines. Ventral paratabulation intermediate between L- and S-type sulcal organization, exhibiting a sigmoidal parasulcus and a 1’/6’’ ventral arrangement. Prominent septum may surround antapical paraplate 1’’’’, particularly at the ps/ 1’’’’ junction. Expression of postcingular paraplate 1j and sulcal paraplates commonly suppressed. Archeopyle precingular (3’’). Operculum free. Endophragm and periphragm typically appressed, except at the apex where the periphragm may form a short apical horn and occasionally at the antapex where an antapical pericoel may be evident. Phragma sparsely and irregularly granulate.
Description: A medium-sized, proximochorate, cornucavate cyst with a subspherical to polyhedral ambitus; a weakly developed apical horn is also usually present. Cingular cross-section subcircular with a slight indentation in the parasulcal area. The cyst wall is two-layered and variably cornucavate. The endophragm and periphragm are closely appressed, except at the apex where a short apical horn is formed, and very occasionally at the antapex, when a hypopericoel may be evident. The paratabulation is indicated by continuous parasutural septa surmounted by anchor-like processes (Fig. 7A,B). Processes are typically flat, solid, with wide bases tapering to a narrower neck, and distally bifid with distinctly recurved termini resulting in anchor shaped extremities, or rarely simply acuminate. Processes are variable in length and distribution; minute, isolated processes are sparsely distributed along the low paracingular crests; evenly spaced longer processes surmount the parasutural crests away from the parasulcus and paracingulum; long, often acuminate, processes are located at the antapical gonal points. Low to high intratabular granules are widely scattered on the periphragm surface. The parasutural septa delineate a gonyaulacacean paratabulation with an intermediate L- and S-type ventral organization and a sinistrally helicoid cingulum. Paratabulation formula: Pr, 4’, 6’’, 6c, 5s, 6’’’, 1p, 1’’’’. A small preapical paraplate (Q) is occasionally evident on the apical horn. The first (1’) and fourth (4’) apical paraplates are narrow and elongated, both are Fparallel-sided; but the first apical paraplate (1’) typically extends farther posteriorly and possesses a short contact with the sixth precingular paraplate (6’’), thus precluding any contact between the anterior sulcal paraplate (as) and the fourth apical paraplate (4’). This is the 1’/6’’ ventral arrangement of Helenes (1986, pp. 80– 81). The sixth precingular paraplate (6W) is elongated, curved, and pentagonal. The expression of the sulcal paraplates is commonly suppressed but low parasutural crests occur intermittently (Fig. 7C,D). The parasulcus is weakly sigmoidal and narrowest between the ends of the paracingulum. The paracingulum ends are offset by twice their breadth and are aligned, not overhanging. The first postcingular paraplate (1’’’) is reduced and projects into the parasulcus. The fourth postcingular paraplate (4’’’) is located symmetrically below the third precingular paraplate (3’’), indicating neutral torsion of the epi- and hypocysts. A distinctly curved posterior intercalary paraplate (1p) is sited between the second postcingular paraplate (2’’’) and the asymmetrical sexiform antapical paraplate (1’’’’). Prominent septum is rarely developed surrounding the antapical paraplate (1’’’’), particularly at the ps/1’’’’ contact. The archeopyle is precingular, type P3’’. Operculum is free and may be preserved within the cyst body. Paraplate 3’’ is strongly geniculate.
Dimensions (based on 23 specimens): Length of cyst (excluding processes), 40 (51) 56 µm; width of cyst (excluding processes), 33 (42) 50 µm; thickness of cyst wall, 0.5 (1) 1.5 µm; length of processes, 1 (3) 7 µm; height of septa (excluding processes), 1 (1.5) 5 µm.
Holotype: Length of cyst (excluding processes), 52 µm; width of cyst (excluding processes), 40 µm; thickness of cyst wall, 1 µm; length of processes, 2– 4 µm; height of septa (excluding processes), 1–2 µm.
Remarks: Prominent anchor-tipped processes surmounting relatively low parasutural crests characterize Leptodinium? ancoralium sp. nov. The crests are much-reduced or absent around the parasulcus and paracingulum, but are more prominent near the antapex, where the endophragm and periphragm are rarely separated to form a small hypopericoel. The parasutural septa surrounding the antapical paraplate (1’’’’) may form high (3–6 µm) perforate crests.
Variable dorsoventral outline, stunted apical horn, irregular occurrence of a hypopericoel, and intermediate L-/S-type ventral organization cause some difficulty in generic attribution. The new species is provisionally assigned to Leptodinium Klement, 1960 emend. Stover and Evitt, 1978 as it possesses a similar paratabulation including a 1’/6’’ ventral arrangement, an asymmetrical antapical paraplate (1’’’’), and generally lacks cavation, other than the formation of the apical horn by the periphragm (cornucavate). Leptodinium? ancoralium diverges from Stover and Evitt’s (1978) emendation of the genus in having only a short 4’/6’’ contact and in occasionally possessing a cavate antapex. Although featuring an asymmetrical antapical paraplate (1’’’’) and lacking obvious incidentals, some aspects of the paratabulation of this species are closer to Gonyaulacysta Deflandre, 1964 emend. Helenes and Lucas-Clark, 1997 than to Leptodinium. The narrow, elongated, Fparallel-sided first (1’) and fourth (4’) apical paraplates, with the first apical paraplate (1’) extending farther posteriorly is a trait typically associated with Gonyaulacysta. Indeed, if specimens of L? ancoralium with well-developed antapical cavation were recorded exclusively they would probably be assigned to Gonyaulacysta. The development of antapical cavation in L? ancoralium is not common; most specimens recorded exhibited only limited apical cavation (Fig. 8A–C). Species of Gonyaulacysta are typically bicavate, with well-developed epi- and hypopericoels and attribution of the new species to Leptodinium was thus preferred. Leptodinium? ancoralium has a roughly circular cingular cross-section (only slight sulcal indentation is apparent), which differentiates it further from Gonyaulacysta, which is dorso-ventrally compressed. Gonyaulacysta is also distinguished by its possession of two anterior dorsal intercalary paraplates, an as/2’’’ contact, and the common presence of an antapical claustrum.
The paratabulation pattern and degree of cavation exhibited by L? ancoralium superficially resembles that of Stanfordella Helenes and Lucas-Clark, 1997 but critically it lacks the 1’/5’’ (1u/6) contact that distinguishes this genus. The new species is also morphologically similar to Impagidinium Stover and Evitt, 1978 and possesses several features indicative of an S-type ventral organization: sigmoidal shape of the parasulcus; marked offset of the ends of paracingulum; and the typically suppressed expression of the paraplates within the parasulcus. However, the contact between the first apical paraplate (1’) and the sixth precingular paraplate (6’’) precludes the contact between the anterior sulcal paraplate (as) and fourth apical paraplate (4’’) that is standard in typical S-type ventral organization. Furthermore, Impagidinium differs in having a triangular precingular paraplate (6’’), typically lacking an apical horn, and the often incompletely expressed paratabulation.
Comparison: The anchor-tipped processes surmounting smooth parasutural septa, short apical horn, and occasional development of antapical cavation characterize L? ancoralium. Leptodinium sepimentum Stevens and Helby, 1987 superficially resembles L? ancoralium but differs in paratabulation and in bearing baculate processes or rarely discontinuous perforate septa with denticulate crests along its parasutures. Leptodinium? ancoralium differs from most other species within the genus in possessing a degree of cavation and having ornamented parasutural septa. Gonyaulacysta pectinigera (Gocht, 1970) Fensome (1979) has a comparable morphology to L? ancoralium and possesses a broadly similar paratabulation but is distinguished by its distinctive pentagonal shape, narrower apical horn, and higher denticulate and spinose parasutural crests. These denticles and spines occasionally bifurcate but do not resemble the characteristic anchor-tipped processes of L? ancoralium. Atypical specimens of L? ancoralium exhibiting bicavation (e.g., Fig. 8C) may recall Gonyaulacysta eisenackii (Deflandre, 1939) Sarjeant, 1982, which features variable antapical cavation, but is readily separable by its coarser and higher parasutural crests surmounted by long, pointed spines.
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Questionable assignment: Mantle (2005, p.256).
Holotype: Mantle, 2005, pl.3, figs.4–7.
Age: Callovian–early Oxfordian.
---------------------------------------------
Original description (Mantle, 2005):
Leptodinium? ancoralium sp. nov. (Plate III, 1–9; Figs. 7A–D, 8A–C).
Holotype and type locality: Challis-11 ST1 well, sidewall core sample at 1552.50 m, Slide no. 3, EF N27/1. CPC no. 38827 (Plate III, 4–7).
Etymology: Latin, ancoralis; with reference to the anchor-shaped processes surmounting the parasutural crests.
Diagnosis: Cysts subspherical, ovoidal, or polyhedral, proximochorate, typically cornucavate, medium-sized with a circular cingular cross-section. Gonyaulacacean paratabulation indicated by parasutural septa surmounted by bifurcating, anchor-like spines. Ventral paratabulation intermediate between L- and S-type sulcal organization, exhibiting a sigmoidal parasulcus and a 1’/6’’ ventral arrangement. Prominent septum may surround antapical paraplate 1’’’’, particularly at the ps/ 1’’’’ junction. Expression of postcingular paraplate 1j and sulcal paraplates commonly suppressed. Archeopyle precingular (3’’). Operculum free. Endophragm and periphragm typically appressed, except at the apex where the periphragm may form a short apical horn and occasionally at the antapex where an antapical pericoel may be evident. Phragma sparsely and irregularly granulate.
Description: A medium-sized, proximochorate, cornucavate cyst with a subspherical to polyhedral ambitus; a weakly developed apical horn is also usually present. Cingular cross-section subcircular with a slight indentation in the parasulcal area. The cyst wall is two-layered and variably cornucavate. The endophragm and periphragm are closely appressed, except at the apex where a short apical horn is formed, and very occasionally at the antapex, when a hypopericoel may be evident. The paratabulation is indicated by continuous parasutural septa surmounted by anchor-like processes (Fig. 7A,B). Processes are typically flat, solid, with wide bases tapering to a narrower neck, and distally bifid with distinctly recurved termini resulting in anchor shaped extremities, or rarely simply acuminate. Processes are variable in length and distribution; minute, isolated processes are sparsely distributed along the low paracingular crests; evenly spaced longer processes surmount the parasutural crests away from the parasulcus and paracingulum; long, often acuminate, processes are located at the antapical gonal points. Low to high intratabular granules are widely scattered on the periphragm surface. The parasutural septa delineate a gonyaulacacean paratabulation with an intermediate L- and S-type ventral organization and a sinistrally helicoid cingulum. Paratabulation formula: Pr, 4’, 6’’, 6c, 5s, 6’’’, 1p, 1’’’’. A small preapical paraplate (Q) is occasionally evident on the apical horn. The first (1’) and fourth (4’) apical paraplates are narrow and elongated, both are Fparallel-sided; but the first apical paraplate (1’) typically extends farther posteriorly and possesses a short contact with the sixth precingular paraplate (6’’), thus precluding any contact between the anterior sulcal paraplate (as) and the fourth apical paraplate (4’). This is the 1’/6’’ ventral arrangement of Helenes (1986, pp. 80– 81). The sixth precingular paraplate (6W) is elongated, curved, and pentagonal. The expression of the sulcal paraplates is commonly suppressed but low parasutural crests occur intermittently (Fig. 7C,D). The parasulcus is weakly sigmoidal and narrowest between the ends of the paracingulum. The paracingulum ends are offset by twice their breadth and are aligned, not overhanging. The first postcingular paraplate (1’’’) is reduced and projects into the parasulcus. The fourth postcingular paraplate (4’’’) is located symmetrically below the third precingular paraplate (3’’), indicating neutral torsion of the epi- and hypocysts. A distinctly curved posterior intercalary paraplate (1p) is sited between the second postcingular paraplate (2’’’) and the asymmetrical sexiform antapical paraplate (1’’’’). Prominent septum is rarely developed surrounding the antapical paraplate (1’’’’), particularly at the ps/1’’’’ contact. The archeopyle is precingular, type P3’’. Operculum is free and may be preserved within the cyst body. Paraplate 3’’ is strongly geniculate.
Dimensions (based on 23 specimens): Length of cyst (excluding processes), 40 (51) 56 µm; width of cyst (excluding processes), 33 (42) 50 µm; thickness of cyst wall, 0.5 (1) 1.5 µm; length of processes, 1 (3) 7 µm; height of septa (excluding processes), 1 (1.5) 5 µm.
Holotype: Length of cyst (excluding processes), 52 µm; width of cyst (excluding processes), 40 µm; thickness of cyst wall, 1 µm; length of processes, 2– 4 µm; height of septa (excluding processes), 1–2 µm.
Remarks: Prominent anchor-tipped processes surmounting relatively low parasutural crests characterize Leptodinium? ancoralium sp. nov. The crests are much-reduced or absent around the parasulcus and paracingulum, but are more prominent near the antapex, where the endophragm and periphragm are rarely separated to form a small hypopericoel. The parasutural septa surrounding the antapical paraplate (1’’’’) may form high (3–6 µm) perforate crests.
Variable dorsoventral outline, stunted apical horn, irregular occurrence of a hypopericoel, and intermediate L-/S-type ventral organization cause some difficulty in generic attribution. The new species is provisionally assigned to Leptodinium Klement, 1960 emend. Stover and Evitt, 1978 as it possesses a similar paratabulation including a 1’/6’’ ventral arrangement, an asymmetrical antapical paraplate (1’’’’), and generally lacks cavation, other than the formation of the apical horn by the periphragm (cornucavate). Leptodinium? ancoralium diverges from Stover and Evitt’s (1978) emendation of the genus in having only a short 4’/6’’ contact and in occasionally possessing a cavate antapex. Although featuring an asymmetrical antapical paraplate (1’’’’) and lacking obvious incidentals, some aspects of the paratabulation of this species are closer to Gonyaulacysta Deflandre, 1964 emend. Helenes and Lucas-Clark, 1997 than to Leptodinium. The narrow, elongated, Fparallel-sided first (1’) and fourth (4’) apical paraplates, with the first apical paraplate (1’) extending farther posteriorly is a trait typically associated with Gonyaulacysta. Indeed, if specimens of L? ancoralium with well-developed antapical cavation were recorded exclusively they would probably be assigned to Gonyaulacysta. The development of antapical cavation in L? ancoralium is not common; most specimens recorded exhibited only limited apical cavation (Fig. 8A–C). Species of Gonyaulacysta are typically bicavate, with well-developed epi- and hypopericoels and attribution of the new species to Leptodinium was thus preferred. Leptodinium? ancoralium has a roughly circular cingular cross-section (only slight sulcal indentation is apparent), which differentiates it further from Gonyaulacysta, which is dorso-ventrally compressed. Gonyaulacysta is also distinguished by its possession of two anterior dorsal intercalary paraplates, an as/2’’’ contact, and the common presence of an antapical claustrum.
The paratabulation pattern and degree of cavation exhibited by L? ancoralium superficially resembles that of Stanfordella Helenes and Lucas-Clark, 1997 but critically it lacks the 1’/5’’ (1u/6) contact that distinguishes this genus. The new species is also morphologically similar to Impagidinium Stover and Evitt, 1978 and possesses several features indicative of an S-type ventral organization: sigmoidal shape of the parasulcus; marked offset of the ends of paracingulum; and the typically suppressed expression of the paraplates within the parasulcus. However, the contact between the first apical paraplate (1’) and the sixth precingular paraplate (6’’) precludes the contact between the anterior sulcal paraplate (as) and fourth apical paraplate (4’’) that is standard in typical S-type ventral organization. Furthermore, Impagidinium differs in having a triangular precingular paraplate (6’’), typically lacking an apical horn, and the often incompletely expressed paratabulation.
Comparison: The anchor-tipped processes surmounting smooth parasutural septa, short apical horn, and occasional development of antapical cavation characterize L? ancoralium. Leptodinium sepimentum Stevens and Helby, 1987 superficially resembles L? ancoralium but differs in paratabulation and in bearing baculate processes or rarely discontinuous perforate septa with denticulate crests along its parasutures. Leptodinium? ancoralium differs from most other species within the genus in possessing a degree of cavation and having ornamented parasutural septa. Gonyaulacysta pectinigera (Gocht, 1970) Fensome (1979) has a comparable morphology to L? ancoralium and possesses a broadly similar paratabulation but is distinguished by its distinctive pentagonal shape, narrower apical horn, and higher denticulate and spinose parasutural crests. These denticles and spines occasionally bifurcate but do not resemble the characteristic anchor-tipped processes of L? ancoralium. Atypical specimens of L? ancoralium exhibiting bicavation (e.g., Fig. 8C) may recall Gonyaulacysta eisenackii (Deflandre, 1939) Sarjeant, 1982, which features variable antapical cavation, but is readily separable by its coarser and higher parasutural crests surmounted by long, pointed spines.
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