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Thalassiphora subreticulata
Thalassiphora subreticulata n.sp., Mudie, P. J. et al., 2019
Holotype: Mudie, P. J. et al., 2019, Plate 1, Figures 19−20. Slide P37296-01
Original description: Mudie, P. J. et al., 2019:
Diagnosis:
A species of Thalassiphora similar to Thalassiphora pelagica but with a periphragm that has a coarse and unevenly reticulate structure. The large endocyst is subspherical to elliptical or subrhomboidal, commonly in an eccentric position when viewed dorso-ventrally. The endophragm is generally granulose or shagreenate to lanuginose (woolly), the ornament giving it a spongy appearance when viewed by light microscopy (LM) and a lanuginose to papillose texture in scanning electron microscope (SEM) images.
Description:
Shape: The pericyst outline is irregularly rounded to polygonal in dorso-ventral and lateralviews, enveloping a darker, more robust endocyst that is generally subspheroidal or subovoidal to subrhomboidal and 50–75% the diameter of that of the pericyst.
Endocyst: distinctly offset laterally as seen in dorso-ventral view (Pl. 1, Figs. 1–2, 5–6, 13–14, 17–18)
Pericoel: absent over a dorsal area of variable size, but becomes progressively wider towards the ventral surface, where the periphragm culminates in a more or less uneven margin surrounding an opening in the pericyst over the ventral region; this opening is discernable with difficulty in LM images but is clearly seen using SEM. Pericyst: may appear bilaterally wing-like, with the wings joined at apex and antapex.The dorso-ventral outline of the pericyst is typically very irregular because of undulations, folds or tears; rarely it is almost spherical to sub-rhomboidal. In dorso-ventral view the outline of the endocyst is uniform, but commonly has a narrow (3−5 μm wide) marginal ledge or flange.
Wall structure: The endophragm appears to be two-layered, typically about 5 μm in total thickness, with a thin, inner endophragm layer, usually with a microgranular inner surface, but sometimes smooth. The thicker outer endophragm layer appears to be discontinuously tectate and has a characteristically granulose or shagreenate
to lanuginose outer surface, giving a spongy appearance in LM images, and a woolly to papillose texture in SEM images. The fibrous-membranous periphragm is
generally relatively thin, with a roughly reticulate structure that stretches into fibrils at the junction between the periphragm and endophragm surface dorsally. In ventral view, some parts of the endophragm laterally show parallel strands of fibrils that are attached ventrally, but in other parts, the attachment fibrils are entirely hidden on the dorsal surface behind the compressed endocyst margin or flange. This fibril arrangement is like that in SEM images of the C-form of Thalassiphora pelagica
(Benedek and Gocht 1981a, pl. 3, figs. 1a, 3a), but no vertical fibrillar strands occur on the endocyst in Thalassiphora subreticulata. The reticulum of the periphragm is variable, generally with irregularly shaped openings that increase in size ventrally (i.e. away from the endophragm), except where it tends to “in-roll” at the outer margin; there, it is usually finely perforate and may appear cord-like. Thinned areas of the periphragm appear microreticulate or microporate in LM images; SEM images show that many perforations are crossed by intact or broken fibrils. The periphragm is smooth or microgranulate, with a fine to coarsely microfibrous texture that produces notable irregularity in the periphragm surface and margin.
Archeopyle: The P3” archeopyle is relatively large and usually open, being almost as broad as it is high, with a sub-pentagonal, camerate to round-arched shape. It appears to be reduced, as is characteristic of many cribroperinoidean cysts (Fensome et al. 1993, text-fig. 89). The operculum is usually free, but is rarely closed or occasionally attached and it lacks an archeopyle spine. No archeopyle spine was seen on any specimens.
Tabulation: Specimens are usually laterally oriented and the tabulation is difficult to discern beyond traces of the cingulum; the ventral endocyst surfaces of SEM images lack any trace of tabulation. The base of the archeopyle is usually flanked by one of two low ridges that delimit a narrow, shallow cingulum, which extends for a variable length on the periphragm over the pericoel, as seen in dorsal or lateral view but not ventral view. The periphragm perforations are highly variable in shape and distribution and seem not to be related to tabulation. Other low ridges on dorsal and lateral surfaces of the endocyst suggest plate sutures 2”/3”, 4”/ 5” and around *1””, but equivalent structures are generally weakly discernable or absent on the periphragm except for possible traces of the cingulum. Evidence for a mid-dorsal position of the *4’”/*5’” plate boundary on SEM images of cysts is unclear but some LM images may show faint traces of this boundary. The apical area is notably thickened or ridged with a small spine possibly marking the 2’/3’ plate boundary.
Dimensions:
A large cyst (63–148 μm total size; 12 specimens measured).
Endocyst length = 46 (63) 90 μm, width = 47 (62) 83 μm. Pericyst length = 63 (103) 125 μm, width = 73 (103) 148 μm. Maximum pericoel width = 20 (34) 51 μm. Archeopyle average length x width = 26 x 25 μm.
Remarks:
The pericoel varies in width and also symmetry, from appearing equally wide on either side in lateral view to, more usually, wider on the left and narrower or folded on the right. In Thalassiphora subreticulata, any projections appear to represent folds or tears in the periphragm, which appears to be relatively easily compressed and torn. A few specimens have a reduced pericoel, forming a series of perforate crest-like structures in the pericyst outline; but no acavate specimens (equivalent to the
“proximate” cyst forms of Benedek and Gocht 1981b) have been found.
Light microscope images show that this cyst varies in degree of reticulation, being irregularly perforate with openings of variable shape randomly crossed by fibrils. The irregularly-shaped periphragm perforations tend to increase in number and size towards the outer edge of the membrane, as seen in ventral view. A few perforations in
Thalassiphora subreticulata are associated with sub-rounded, raised areas of the periphragm. However, the irregular, fibril-crossed perforations in Thalassiphora
subreticulata appear as if pulled apart by stretching of a microreticulate network, in contrast to what might be envisaged by bursting a bubble. The geometrical consequences of pulling out the edges of an initially evenly-distributed network of microfibrils will result in an uneven network pattern, referred to here as a “stretched-net model”.
Affinities:
Thalassiphora subreticulata is superficially similar to Thalassiphora pelagica, Thalassiphora fenestrata and Thalassiphora microperforata. Thalassiphora subreticulata is smaller (pericyst length <125 μm), with a fibrous, perforate periphragm that is coarsely and irregularly reticulate, and most commonly has an apparently eccentrically positioned endocyst when seen in dorso-ventral view. The holotype species Thalassiphora fenestrata also appears to show strong eccentricity but its periphragm is torn; other illustrated specimens (e.g. Heilmann-lausen and Van Simaeys 2005, pl. 12, figs. 4,5) show a symmetrically located endocyst.
Thalassiphora fenestrata also differs from Thalassiphora subreticulata in being larger (with a maximum dimension of 150 μm) and has large, open, rounded fenestrations in lateral and distal parts of its periphragm. Thalassiphora microperforata is also larger (141–174 μm), and has a densely perforate, membranous periphragm that is largely attached over the ventral surface, and has only a small circular opening above the archeopyle.
Thalassiphora subreticulata superficially resembles Thalassiphora balcanica in size and periphragm structure, but the thinner, membranous periphragm of Thalassiphora balcanica typically enfolds a larger area of the ventral surface, sometimes has a few large claustra (arch-shaped openings), and may have supporting folds in the polar areas. The periphragm of Thalassiphora reticulata is thinner, with a finer texture and more uniform distribution of smaller, rounded perforations, giving it a “clean-cut” appearance, with a generally better-defined reticulate structure or network. Thalassiphora delicata is clearly distinguished by its non-fibrous walls that are smooth or microperforate; also it has a centrally located endocyst. Thalassiphora bononiensis also has a coarsely and irregularly reticulate periphragm, described as “lightly fibrous”, but differs in having a thinner (2 μm-thick), punctate endophragm, and a periphragm described as arising as sutural crests that are proximally united (Corradini 1973). The
periphragm in Thalassiphora bononiensis arises from the dorsal surface and forms a circular, helmet-shaped structure. LM images of the holotype (Corradini 1972, pl. 30, figs. 6a, 6b) show the periphragm opening toward the ventral surface but one SEM image (ibid, pl. 38, fig. 1) shows a periphragm open toward the dorsal archeopyle as in genus Invertoysta.
Holotype: Mudie, P. J. et al., 2019, Plate 1, Figures 19−20. Slide P37296-01
Original description: Mudie, P. J. et al., 2019:
Diagnosis:
A species of Thalassiphora similar to Thalassiphora pelagica but with a periphragm that has a coarse and unevenly reticulate structure. The large endocyst is subspherical to elliptical or subrhomboidal, commonly in an eccentric position when viewed dorso-ventrally. The endophragm is generally granulose or shagreenate to lanuginose (woolly), the ornament giving it a spongy appearance when viewed by light microscopy (LM) and a lanuginose to papillose texture in scanning electron microscope (SEM) images.
Description:
Shape: The pericyst outline is irregularly rounded to polygonal in dorso-ventral and lateralviews, enveloping a darker, more robust endocyst that is generally subspheroidal or subovoidal to subrhomboidal and 50–75% the diameter of that of the pericyst.
Endocyst: distinctly offset laterally as seen in dorso-ventral view (Pl. 1, Figs. 1–2, 5–6, 13–14, 17–18)
Pericoel: absent over a dorsal area of variable size, but becomes progressively wider towards the ventral surface, where the periphragm culminates in a more or less uneven margin surrounding an opening in the pericyst over the ventral region; this opening is discernable with difficulty in LM images but is clearly seen using SEM. Pericyst: may appear bilaterally wing-like, with the wings joined at apex and antapex.The dorso-ventral outline of the pericyst is typically very irregular because of undulations, folds or tears; rarely it is almost spherical to sub-rhomboidal. In dorso-ventral view the outline of the endocyst is uniform, but commonly has a narrow (3−5 μm wide) marginal ledge or flange.
Wall structure: The endophragm appears to be two-layered, typically about 5 μm in total thickness, with a thin, inner endophragm layer, usually with a microgranular inner surface, but sometimes smooth. The thicker outer endophragm layer appears to be discontinuously tectate and has a characteristically granulose or shagreenate
to lanuginose outer surface, giving a spongy appearance in LM images, and a woolly to papillose texture in SEM images. The fibrous-membranous periphragm is
generally relatively thin, with a roughly reticulate structure that stretches into fibrils at the junction between the periphragm and endophragm surface dorsally. In ventral view, some parts of the endophragm laterally show parallel strands of fibrils that are attached ventrally, but in other parts, the attachment fibrils are entirely hidden on the dorsal surface behind the compressed endocyst margin or flange. This fibril arrangement is like that in SEM images of the C-form of Thalassiphora pelagica
(Benedek and Gocht 1981a, pl. 3, figs. 1a, 3a), but no vertical fibrillar strands occur on the endocyst in Thalassiphora subreticulata. The reticulum of the periphragm is variable, generally with irregularly shaped openings that increase in size ventrally (i.e. away from the endophragm), except where it tends to “in-roll” at the outer margin; there, it is usually finely perforate and may appear cord-like. Thinned areas of the periphragm appear microreticulate or microporate in LM images; SEM images show that many perforations are crossed by intact or broken fibrils. The periphragm is smooth or microgranulate, with a fine to coarsely microfibrous texture that produces notable irregularity in the periphragm surface and margin.
Archeopyle: The P3” archeopyle is relatively large and usually open, being almost as broad as it is high, with a sub-pentagonal, camerate to round-arched shape. It appears to be reduced, as is characteristic of many cribroperinoidean cysts (Fensome et al. 1993, text-fig. 89). The operculum is usually free, but is rarely closed or occasionally attached and it lacks an archeopyle spine. No archeopyle spine was seen on any specimens.
Tabulation: Specimens are usually laterally oriented and the tabulation is difficult to discern beyond traces of the cingulum; the ventral endocyst surfaces of SEM images lack any trace of tabulation. The base of the archeopyle is usually flanked by one of two low ridges that delimit a narrow, shallow cingulum, which extends for a variable length on the periphragm over the pericoel, as seen in dorsal or lateral view but not ventral view. The periphragm perforations are highly variable in shape and distribution and seem not to be related to tabulation. Other low ridges on dorsal and lateral surfaces of the endocyst suggest plate sutures 2”/3”, 4”/ 5” and around *1””, but equivalent structures are generally weakly discernable or absent on the periphragm except for possible traces of the cingulum. Evidence for a mid-dorsal position of the *4’”/*5’” plate boundary on SEM images of cysts is unclear but some LM images may show faint traces of this boundary. The apical area is notably thickened or ridged with a small spine possibly marking the 2’/3’ plate boundary.
Dimensions:
A large cyst (63–148 μm total size; 12 specimens measured).
Endocyst length = 46 (63) 90 μm, width = 47 (62) 83 μm. Pericyst length = 63 (103) 125 μm, width = 73 (103) 148 μm. Maximum pericoel width = 20 (34) 51 μm. Archeopyle average length x width = 26 x 25 μm.
Remarks:
The pericoel varies in width and also symmetry, from appearing equally wide on either side in lateral view to, more usually, wider on the left and narrower or folded on the right. In Thalassiphora subreticulata, any projections appear to represent folds or tears in the periphragm, which appears to be relatively easily compressed and torn. A few specimens have a reduced pericoel, forming a series of perforate crest-like structures in the pericyst outline; but no acavate specimens (equivalent to the
“proximate” cyst forms of Benedek and Gocht 1981b) have been found.
Light microscope images show that this cyst varies in degree of reticulation, being irregularly perforate with openings of variable shape randomly crossed by fibrils. The irregularly-shaped periphragm perforations tend to increase in number and size towards the outer edge of the membrane, as seen in ventral view. A few perforations in
Thalassiphora subreticulata are associated with sub-rounded, raised areas of the periphragm. However, the irregular, fibril-crossed perforations in Thalassiphora
subreticulata appear as if pulled apart by stretching of a microreticulate network, in contrast to what might be envisaged by bursting a bubble. The geometrical consequences of pulling out the edges of an initially evenly-distributed network of microfibrils will result in an uneven network pattern, referred to here as a “stretched-net model”.
Affinities:
Thalassiphora subreticulata is superficially similar to Thalassiphora pelagica, Thalassiphora fenestrata and Thalassiphora microperforata. Thalassiphora subreticulata is smaller (pericyst length <125 μm), with a fibrous, perforate periphragm that is coarsely and irregularly reticulate, and most commonly has an apparently eccentrically positioned endocyst when seen in dorso-ventral view. The holotype species Thalassiphora fenestrata also appears to show strong eccentricity but its periphragm is torn; other illustrated specimens (e.g. Heilmann-lausen and Van Simaeys 2005, pl. 12, figs. 4,5) show a symmetrically located endocyst.
Thalassiphora fenestrata also differs from Thalassiphora subreticulata in being larger (with a maximum dimension of 150 μm) and has large, open, rounded fenestrations in lateral and distal parts of its periphragm. Thalassiphora microperforata is also larger (141–174 μm), and has a densely perforate, membranous periphragm that is largely attached over the ventral surface, and has only a small circular opening above the archeopyle.
Thalassiphora subreticulata superficially resembles Thalassiphora balcanica in size and periphragm structure, but the thinner, membranous periphragm of Thalassiphora balcanica typically enfolds a larger area of the ventral surface, sometimes has a few large claustra (arch-shaped openings), and may have supporting folds in the polar areas. The periphragm of Thalassiphora reticulata is thinner, with a finer texture and more uniform distribution of smaller, rounded perforations, giving it a “clean-cut” appearance, with a generally better-defined reticulate structure or network. Thalassiphora delicata is clearly distinguished by its non-fibrous walls that are smooth or microperforate; also it has a centrally located endocyst. Thalassiphora bononiensis also has a coarsely and irregularly reticulate periphragm, described as “lightly fibrous”, but differs in having a thinner (2 μm-thick), punctate endophragm, and a periphragm described as arising as sutural crests that are proximally united (Corradini 1973). The
periphragm in Thalassiphora bononiensis arises from the dorsal surface and forms a circular, helmet-shaped structure. LM images of the holotype (Corradini 1972, pl. 30, figs. 6a, 6b) show the periphragm opening toward the ventral surface but one SEM image (ibid, pl. 38, fig. 1) shows a periphragm open toward the dorsal archeopyle as in genus Invertoysta.