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Egmontodinium elongatum
Egmontodinium elongatum Mantle, 2005, p.253,255,256, pl.2, figs.1–9; text-figs.6A–B.
Holotype: Mantle, 2005, pl. 2, figs.4–5, text-figs.6A–B.
Age: Callovian–early Oxfordian.
Original description (Mantle, 2005):
Egmontodinium elongatum sp. nov. (Plate II, 1–9; Fig. 6A,B).
Holotype and type locality: Challis 11 ST1 well, sidewall core at 1552.50 m, Slide no. 2, EF R40/1. CPC no. 38825 (Plate II, 4, 5).
Etymology: Latin, elongatus (elongate); with reference to the large length to width ratio of the outline.
Diagnosis: Cysts proximochorate, acavate, ambitus elongate-ellipsoidal. Wall single-layered; autophragm smooth to scabrate. Gonyaulacalean paratabulation indicated by high membranous septa that form a coarse reticulum with characteristic elongate, rectangular lumina on the pre- and postcingular paraplates. Solid, distally furcate processes interspersed along the parasutural septa and in intratabular positions on the precingular, postcingular, and antapical paraplates. Apical archeopyle, occasionally attached, type (tA). Description: A proximochorate, acavate cyst with an elongate–ellipsoidal or rarely ovoidal ambitus; apices rounded; cyst length is typically almost twice cyst width. Length of epicyst is equal to or slightly less than that of hypocyst. The cyst wall is apparently single-layered; autophragm typically 1.5 µm thick; laevigate to scabrate. Autophragm bears coarse reticulum formed by membranous, distally smooth septa, 3–7 µm high that form elongate, rectangular lumina on the preand postcingular paraplates and variable parasutural lumina elsewhere on the cyst. Reticulum reflects the cysts paratabulation (Fig. 6). Laevigate, solid processes of variable width (1–5 µm) and branching distally (usually bi- or trifurcate) are interspersed along the septa. Isolated processes are commonly present in intratabular positions, particularly on the pre- and postcingular paraplates and occasionally at the antapex. The antapical and postcingular processes may display fenestrate branching at their bases. The septa are predominantly parasutural and appear to indicate a gonyaulacalean paratabulation with the formula: pr, 4’, 6’’, ?6c, ?s, 6’’’, 1p, 1’’’’. The septa infrequently bifurcate and diverge from the parasutures thus forming small lumina that do not delineate paraplate boundaries. The precingular paraplates are elongate and may have reduced septa along their anterior borders. These septa typically remain attached to the operculum after dehiscence, but a fraction of the septa may stay adhered to the anterior end of the precingular paraplates. The first postcingular paraplate (1’’’) is much-reduced. The antapical paraplate (1’’’’) often appears partially subdivided but the septa forming this part of the reticulum are intratabular features. Archeopyle is apical, type (tA). Operculum is simple and typically free but may rarely remain attached. The constituent apical paraplates are not clearly delimited, apart from the operculum outline. A deeply indented, narrow sulcal notch is present on the weakly angular apical margin. The paracingulum is laevorotatory and displaced by about a cingulum width. The septa that typically delimit the paracingulum are occasionally incomplete, particularly along the posterior border. Parasulcus appears to have an L-type ventral organization but parasutures are typically not expressed within the sulcus. The parasulcus is narrow on the epicyst but distinctly broader on the hypocyst (Fig. 6A).
Dimensions (based on 18 specimens): Total length of loisthocyst, 52 (63) 77 µm; maximum width of cyst, 22 (35) 50 µm; thickness of cyst wall, 11 (1.5) 2 µm; height of septa, 3 (5) 7 µm.
Holotype: Total length of cyst, 73 µm; maximum width of cyst, 38 µm; thickness of cyst wall, 1.5 µm; height of septa, 5 µm.
Remarks: Egmontodinium elongatum sp. nov is characterized by its elongate ellipsoidal ambitus and coarsely reticulate phragma delimited by high, laevigate septa. Its assignment to Egmontodinium Gitmez and Sarjeant, 1972 is based on the paratabulation pattern and the prominent gonal and intergonal processes (see discussion above relating to Stover and Evitt (1978) and Davey, 1979). Ellipsoidictyum Klement, 1960 is irregularly reticulate with weakly developed paratabulation (typically indicated solely by the archeopyle margin and paracingulum). Occasionally parasutural septa are apparent on specimens with a coarse reticulum, but these differ from Egmontodinium in lacking prominent gonal, intergonal, and intratabular processes.
Comparison: Egmontodinium polyplacophorum Gitmez and Sarjeant, 1972, whilst possessing a similar paratabulation to E. elongatum, is characterized by penitabular crests towards the apex and antapex and, moreover, lacks the solid bi- and trifurcating processes of E. elongatum. Egmontodinium torynum (Cookson and Eisenack, 1960) Davey, 1979 has rows of distally furcate processes that are variably linked by low septa or completely unconnected. This contrasts with the high, laevigate, membranous septa of E. elongatum. Furthermore, the processes of E. torynum are longer and more closely spaced than those of E. elongatum. Egmontodinium expiratum Davey, 1982 is morphologically intermediate between E. polyplacophorum and E. torynum, and has low parasutural crests connecting long flared processes; it is distinguished from E. elongatum by its rounder ambitus and less prominent parasutural septa. The holotype of E. sp. A of Davey, 1979 was redesignated as the holotype of E. expiratum. Egmontodinium minor Kumar, 1987 has a more squat appearance, is shorter (~75%), and lacks the parasutural processes of E. elongatum. Ellipsoidictyum cinctum Klement, 1960 typically possesses a finer, irregular reticulum but may have parasutural septa, particularly on the epicyst. It differs from E. elongatum in having a more spheroidal shape and lacks the prominent gonal, intergonal, and intratabular processes.
Holotype: Mantle, 2005, pl. 2, figs.4–5, text-figs.6A–B.
Age: Callovian–early Oxfordian.
Original description (Mantle, 2005):
Egmontodinium elongatum sp. nov. (Plate II, 1–9; Fig. 6A,B).
Holotype and type locality: Challis 11 ST1 well, sidewall core at 1552.50 m, Slide no. 2, EF R40/1. CPC no. 38825 (Plate II, 4, 5).
Etymology: Latin, elongatus (elongate); with reference to the large length to width ratio of the outline.
Diagnosis: Cysts proximochorate, acavate, ambitus elongate-ellipsoidal. Wall single-layered; autophragm smooth to scabrate. Gonyaulacalean paratabulation indicated by high membranous septa that form a coarse reticulum with characteristic elongate, rectangular lumina on the pre- and postcingular paraplates. Solid, distally furcate processes interspersed along the parasutural septa and in intratabular positions on the precingular, postcingular, and antapical paraplates. Apical archeopyle, occasionally attached, type (tA). Description: A proximochorate, acavate cyst with an elongate–ellipsoidal or rarely ovoidal ambitus; apices rounded; cyst length is typically almost twice cyst width. Length of epicyst is equal to or slightly less than that of hypocyst. The cyst wall is apparently single-layered; autophragm typically 1.5 µm thick; laevigate to scabrate. Autophragm bears coarse reticulum formed by membranous, distally smooth septa, 3–7 µm high that form elongate, rectangular lumina on the preand postcingular paraplates and variable parasutural lumina elsewhere on the cyst. Reticulum reflects the cysts paratabulation (Fig. 6). Laevigate, solid processes of variable width (1–5 µm) and branching distally (usually bi- or trifurcate) are interspersed along the septa. Isolated processes are commonly present in intratabular positions, particularly on the pre- and postcingular paraplates and occasionally at the antapex. The antapical and postcingular processes may display fenestrate branching at their bases. The septa are predominantly parasutural and appear to indicate a gonyaulacalean paratabulation with the formula: pr, 4’, 6’’, ?6c, ?s, 6’’’, 1p, 1’’’’. The septa infrequently bifurcate and diverge from the parasutures thus forming small lumina that do not delineate paraplate boundaries. The precingular paraplates are elongate and may have reduced septa along their anterior borders. These septa typically remain attached to the operculum after dehiscence, but a fraction of the septa may stay adhered to the anterior end of the precingular paraplates. The first postcingular paraplate (1’’’) is much-reduced. The antapical paraplate (1’’’’) often appears partially subdivided but the septa forming this part of the reticulum are intratabular features. Archeopyle is apical, type (tA). Operculum is simple and typically free but may rarely remain attached. The constituent apical paraplates are not clearly delimited, apart from the operculum outline. A deeply indented, narrow sulcal notch is present on the weakly angular apical margin. The paracingulum is laevorotatory and displaced by about a cingulum width. The septa that typically delimit the paracingulum are occasionally incomplete, particularly along the posterior border. Parasulcus appears to have an L-type ventral organization but parasutures are typically not expressed within the sulcus. The parasulcus is narrow on the epicyst but distinctly broader on the hypocyst (Fig. 6A).
Dimensions (based on 18 specimens): Total length of loisthocyst, 52 (63) 77 µm; maximum width of cyst, 22 (35) 50 µm; thickness of cyst wall, 11 (1.5) 2 µm; height of septa, 3 (5) 7 µm.
Holotype: Total length of cyst, 73 µm; maximum width of cyst, 38 µm; thickness of cyst wall, 1.5 µm; height of septa, 5 µm.
Remarks: Egmontodinium elongatum sp. nov is characterized by its elongate ellipsoidal ambitus and coarsely reticulate phragma delimited by high, laevigate septa. Its assignment to Egmontodinium Gitmez and Sarjeant, 1972 is based on the paratabulation pattern and the prominent gonal and intergonal processes (see discussion above relating to Stover and Evitt (1978) and Davey, 1979). Ellipsoidictyum Klement, 1960 is irregularly reticulate with weakly developed paratabulation (typically indicated solely by the archeopyle margin and paracingulum). Occasionally parasutural septa are apparent on specimens with a coarse reticulum, but these differ from Egmontodinium in lacking prominent gonal, intergonal, and intratabular processes.
Comparison: Egmontodinium polyplacophorum Gitmez and Sarjeant, 1972, whilst possessing a similar paratabulation to E. elongatum, is characterized by penitabular crests towards the apex and antapex and, moreover, lacks the solid bi- and trifurcating processes of E. elongatum. Egmontodinium torynum (Cookson and Eisenack, 1960) Davey, 1979 has rows of distally furcate processes that are variably linked by low septa or completely unconnected. This contrasts with the high, laevigate, membranous septa of E. elongatum. Furthermore, the processes of E. torynum are longer and more closely spaced than those of E. elongatum. Egmontodinium expiratum Davey, 1982 is morphologically intermediate between E. polyplacophorum and E. torynum, and has low parasutural crests connecting long flared processes; it is distinguished from E. elongatum by its rounder ambitus and less prominent parasutural septa. The holotype of E. sp. A of Davey, 1979 was redesignated as the holotype of E. expiratum. Egmontodinium minor Kumar, 1987 has a more squat appearance, is shorter (~75%), and lacks the parasutural processes of E. elongatum. Ellipsoidictyum cinctum Klement, 1960 typically possesses a finer, irregular reticulum but may have parasutural septa, particularly on the epicyst. It differs from E. elongatum in having a more spheroidal shape and lacks the prominent gonal, intergonal, and intratabular processes.