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Fibrocysta acornuta
From Fensome et al., 2019:
Fibrocysta acornuta Norris and Jux, 1984, p.161–162, pl.1, figs.17–20; pl.2, figs.1–4; pl.3, fig.5; pl.5, figs.1–6. Holotype: Norris and Jux, 1984, pl.2, figs.1–3. Age: late Kimmeridgian–late Tithonian.
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Original description (Norris and Jux, 1984):
Fibrocysta acornuta sp. nov.
PI. 1, figs. 17-20; Pl. 2, Figs. 1-4; Pl. 3, Fig. 5; PI. 5, Figs. 1-6
Holotype: Slide No. 1451-4U-+4OSw, 51.4x109.0, Palynology Collection, Dept. of Geology, University of Toronto, PI. 2, Figs. 1-3.
Diagnosis: A species of Fibrocysta with an almost globular midbody. Several processes per plate but tabular boundaries obscure. Length of solid spines approximately a fifth of cyst diameter; proximally funnel-shaped and composed of fibrous elements, a slender shaft, and with some of the knobby distal ends connected by fibrils. No prominent apical projection. Surface of the periphragm irregularly microreticulate. Next to the spines endophragm distinct rom periphragm, otherwise closely adpressed. Rounded trapezoidal archeopyle.
Name: acornutum (lat.) = without horn
Dimensions: Overall diameter 40-45 μm; midbody diameter 30-35 μm.
Distribution: Upper Kimmeridgian, Portlandian, and Lower Purbeck Beds (Upper Tithonian) of Dorset and Sussex, Southern England (NORRIS, 1963).
Description:
Light microscopy: (P. 1, Figs. 17-20; Pl. 2, Figs. 1-4): The globular shell with its abundant slender spines (60-80?) has a granular microreticulate suface, sculptural elements measuring 0.4-0.6 μm.The processes (length: 5-12 μm) have a fibrous appearance - at least in their basal, expanded parts. The spines (ø 0.6-0.9 μm) emerge from rootlike structures of the periphragm with their knobby distal ends, occasionally interconnected by fibrils. These fibrils disappear in the solid shafts of the spines.
The tabulation is not discernible from the arrangenments of the many intratabular processes which arise 3-8 μm apart from each other. Plate boundaries are only clear along the polygonal edge of the precingular archeopyle (ø ca. 15 μm). The apical process is only slightly thicker and not much longer than the other processes.
The antapical processes tend to be slightly longer than those on the epitract.
Scanning electron microscopy (Pl. 3, Fig. 5): The sculpture of the periphragm is composed of a trabecular reticulum. From this substrate the solid spines arise without revealing a distinct plate pattern. One exceptionally stout process (left side of specimen in PI. 3, fig. 5) is surmised to mark the apex of the cyst. A precingular position of the archeopyle is therefore indicated. The inner surface of the endophragm is smooth apart from the underside of the projections, where some openings may occur (Pl. 3, fig. 5).
Transmission electron microscopy (Pl. 5, figs. 1-6): Uncomplicated wall structures are shown in the sections though the cordosphaeridiacean construction is at first not evident. The two layers may be fused together (R5, figs. 2, 3), The endophragm is less than 0.1 μm thick and is penetrated by minute pores (0 [sic] ca. 0.02-0.05 μm).
They are abundant below the spines (PL. 5, figs. 1 A, 2A, 4). A zone of tiny cavities (0.1-0.2 μm) marks the boundary with the periphragm (Pl. 5, fig. 3); below the processes, the diameters of these holes may exceed 1 μm. The periphragm is either represented by a 0.1-0.2 μm thick unperforated layer which immediately overlies the endophragm (Pl. 5, fig. 1la, 3), or both layers are separated from each other by radial, septa-like wall structures (Pl. 5, fig. 1 b, 4). These structures may expand the outer layer of the phragma to a spongy matrix in which the processes
are inserted. The proximal ends of the processes are expanded and comprise root-like fibrils; the istal extensions are almost solid (Pl. 5, fig. 2b).
Comparison: The Eocene species F. radiata (MORGENROTH) STOVER and EVITT is of similar size but of more ovoidal shape and with much longer projections compared with F. acornuta. The apical spines in particular in F. radiata are much more distinct. Otherwise such features as the configuration of the archeopyle, the composition of the walls and the construction of the spines are very similar to F. acornuta. F. acornuta does not have a labyrinthic wall structure as in Cordosphaeridium EISENACK, although the proximal parts of the processes are fibrous. Tityrosphaeridium porosispinum (DAVEY) has expanded meshy processes, unlike those of F acornuta, but amalgamated inter-processes walls which resemble the ultrastructure of the phragma of F. acornuta. In this respect the double wall of the hystrsichosphaeridiacean Oligosphaeridium abaculum DAVEY is even more fused together than in Fibrocysta acoronuta sp. nov., yet near the wide tubular and funnel-shaped processes of the former the separated peri- and endophragms are quite evident (JUX, 1980).
The construction of the processes of E acornuta also resembles Spiniferites bentori (ROSSIGNOL), but this gonyaulacacean cyst lacks trabecular elemnents in the wall chambers.
Almost identical structures are present in the inter-process wall of perculodinium centrocarpum (DEFLANDRE and COOKSON) WALL. In this species the two layers have similar dimensions, and their framework is so similar that identical adaptations of the cysts may be indicated. However, the processes of 0. centrocarpum have prominent cavities even in their distal parts (JUx 1976) whereas F. acornuta has a more solid distal process structure.
Fibrocysta acornuta Norris and Jux, 1984, p.161–162, pl.1, figs.17–20; pl.2, figs.1–4; pl.3, fig.5; pl.5, figs.1–6. Holotype: Norris and Jux, 1984, pl.2, figs.1–3. Age: late Kimmeridgian–late Tithonian.
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Original description (Norris and Jux, 1984):
Fibrocysta acornuta sp. nov.
PI. 1, figs. 17-20; Pl. 2, Figs. 1-4; Pl. 3, Fig. 5; PI. 5, Figs. 1-6
Holotype: Slide No. 1451-4U-+4OSw, 51.4x109.0, Palynology Collection, Dept. of Geology, University of Toronto, PI. 2, Figs. 1-3.
Diagnosis: A species of Fibrocysta with an almost globular midbody. Several processes per plate but tabular boundaries obscure. Length of solid spines approximately a fifth of cyst diameter; proximally funnel-shaped and composed of fibrous elements, a slender shaft, and with some of the knobby distal ends connected by fibrils. No prominent apical projection. Surface of the periphragm irregularly microreticulate. Next to the spines endophragm distinct rom periphragm, otherwise closely adpressed. Rounded trapezoidal archeopyle.
Name: acornutum (lat.) = without horn
Dimensions: Overall diameter 40-45 μm; midbody diameter 30-35 μm.
Distribution: Upper Kimmeridgian, Portlandian, and Lower Purbeck Beds (Upper Tithonian) of Dorset and Sussex, Southern England (NORRIS, 1963).
Description:
Light microscopy: (P. 1, Figs. 17-20; Pl. 2, Figs. 1-4): The globular shell with its abundant slender spines (60-80?) has a granular microreticulate suface, sculptural elements measuring 0.4-0.6 μm.The processes (length: 5-12 μm) have a fibrous appearance - at least in their basal, expanded parts. The spines (ø 0.6-0.9 μm) emerge from rootlike structures of the periphragm with their knobby distal ends, occasionally interconnected by fibrils. These fibrils disappear in the solid shafts of the spines.
The tabulation is not discernible from the arrangenments of the many intratabular processes which arise 3-8 μm apart from each other. Plate boundaries are only clear along the polygonal edge of the precingular archeopyle (ø ca. 15 μm). The apical process is only slightly thicker and not much longer than the other processes.
The antapical processes tend to be slightly longer than those on the epitract.
Scanning electron microscopy (Pl. 3, Fig. 5): The sculpture of the periphragm is composed of a trabecular reticulum. From this substrate the solid spines arise without revealing a distinct plate pattern. One exceptionally stout process (left side of specimen in PI. 3, fig. 5) is surmised to mark the apex of the cyst. A precingular position of the archeopyle is therefore indicated. The inner surface of the endophragm is smooth apart from the underside of the projections, where some openings may occur (Pl. 3, fig. 5).
Transmission electron microscopy (Pl. 5, figs. 1-6): Uncomplicated wall structures are shown in the sections though the cordosphaeridiacean construction is at first not evident. The two layers may be fused together (R5, figs. 2, 3), The endophragm is less than 0.1 μm thick and is penetrated by minute pores (0 [sic] ca. 0.02-0.05 μm).
They are abundant below the spines (PL. 5, figs. 1 A, 2A, 4). A zone of tiny cavities (0.1-0.2 μm) marks the boundary with the periphragm (Pl. 5, fig. 3); below the processes, the diameters of these holes may exceed 1 μm. The periphragm is either represented by a 0.1-0.2 μm thick unperforated layer which immediately overlies the endophragm (Pl. 5, fig. 1la, 3), or both layers are separated from each other by radial, septa-like wall structures (Pl. 5, fig. 1 b, 4). These structures may expand the outer layer of the phragma to a spongy matrix in which the processes
are inserted. The proximal ends of the processes are expanded and comprise root-like fibrils; the istal extensions are almost solid (Pl. 5, fig. 2b).
Comparison: The Eocene species F. radiata (MORGENROTH) STOVER and EVITT is of similar size but of more ovoidal shape and with much longer projections compared with F. acornuta. The apical spines in particular in F. radiata are much more distinct. Otherwise such features as the configuration of the archeopyle, the composition of the walls and the construction of the spines are very similar to F. acornuta. F. acornuta does not have a labyrinthic wall structure as in Cordosphaeridium EISENACK, although the proximal parts of the processes are fibrous. Tityrosphaeridium porosispinum (DAVEY) has expanded meshy processes, unlike those of F acornuta, but amalgamated inter-processes walls which resemble the ultrastructure of the phragma of F. acornuta. In this respect the double wall of the hystrsichosphaeridiacean Oligosphaeridium abaculum DAVEY is even more fused together than in Fibrocysta acoronuta sp. nov., yet near the wide tubular and funnel-shaped processes of the former the separated peri- and endophragms are quite evident (JUX, 1980).
The construction of the processes of E acornuta also resembles Spiniferites bentori (ROSSIGNOL), but this gonyaulacacean cyst lacks trabecular elemnents in the wall chambers.
Almost identical structures are present in the inter-process wall of perculodinium centrocarpum (DEFLANDRE and COOKSON) WALL. In this species the two layers have similar dimensions, and their framework is so similar that identical adaptations of the cysts may be indicated. However, the processes of 0. centrocarpum have prominent cavities even in their distal parts (JUx 1976) whereas F. acornuta has a more solid distal process structure.