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Hystrichostrogylon stolidotum
Hystrichstrogylon stolidotum (Duxbury, 1980) Stover and Williams, 1987; emend. Harding, 1990
Originally Diphasiosphaera, subsequently (and now) Hystrichostrogylon.
Holotype: Duxbury, 1980, pl.1, fig. 5; text-fig.6
Locus typicus: Speeton Clay, Speeton, England
Stratum typicum: Barremian
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G.L. Williams short notes on species, Mesozoic-Cenozoic dinocyst course, Urbino, Italy, May 17-22, 1999 - LPP VIEWER CD-ROM 99.5.
Hystrichostrogylon stolidotum (Duxbury, 1980) Stover and Williams, 1987, emend. Harding, 1990b. According to Harding (1990b, p.29), this species has an endocyst barely two-thirds the length of the pericyst and an apical prominence and projecting parasutural processes. Spiniferites type processes extend from parasutures and are of variable height depending on degree of cavation. In cases of extreme cavation, the process terminations only are developed along the parasutural ridges, appearing as a double row of processes. Cavation often complete but there may be contact between the two wall layers dorsally. Paratabulation L-type sexiform, archeopyle precingular, resulting from loss of 3". Ofter a periphragmal claustrum in flagellar scar region. Size: 65-95 x 59-92 µm.
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Original diagnosis: Duxbury, 1980, p.116: Diphasiosphaera stolidota
A cavate dinoflagellate cyst which is distinctly bi-layered and consists of a smooth, spheroidal endoblast and a smooth to finely perforate, spheroidal periblast. The periplast bears a distinct apical projection and has a large sulcal hole. Both body layers are characteristically extensively folded. Apparently typically gonyaulacacean paratabulation is outlined on the periblast by parasutural processes of varying height. The archeopyle is single-paraplate precingular (3"). Around the archeopyle margin, where the two body layers are appressed, the full development of fairly closely-spaced parasutural processes is seen and in this area, parasutural crests may proximally connect the processes. Away from the archeopyle margin and that part of the paracingulum directly posterior to it, the parasutural processes are reduced to a varying extent. As a rule, the greater the distance between the body layers, the shorter the parasutural processes, so that in the ventral area they may be reduced to nothing.
Observed Dimensions: Holotype 86x70 Ám. Overall 95(76)65x92(69)59 Ám.
Emended diagnosis: Harding, 1990, p.29
Shape: Ambitus elongate ovoidal, modified by rare development of apical prominence and projecting parasutural processes. Greatest width across paracingulum. Epicyst and hypocyst equal in length. Endocyst ambitus subcircular to ovoidal, barely two thirds the length of the pericyst. Slight dorso-ventral compression.
Phragma: Periphragm thin 0.3 Ám, with 'orange-peel' surface sculpture. Periphragmal claustrum developed in region of flagellar scar. Spiniferites-type processes extend distally from low ridges which delineate parasutures. The processes are of variable height depending on the degree of cavation. The greater the cavation the shorter the length of the process stalks. Processes bifurcate (or trifurcate if gonal) and may bifurcate again. In cases of extreme cavation the process terminations only are developed along the parasutural ridges, appearing as a double row of processes. Endophragm has a thick wall with a granular surface. Cavation is often complete, but there may be contact between the two wall layers dorsally.
Paratabulation: L-type sexiform gonyaulacoid. Paratabulation formula: 4', 6", 6c, 6''', 1'''', 1p, 5s.
Archaeopyle: Type P4/P4. Opercula both free, monoplacoid.
Paracingulum: In most cases difficult to determine due to collapse of cyst. No indentation in ambital view, laevorotatory, displaced by--2 cingulum widths.
Parasulcus: Periphragmal claustrum in flagellar scar region is often of a very large size (up to 18 µm X 18 µm), similar to that of the archaeopyle. L-type ventral paratabulation developed around this claustrum.
Dimensions: Length (62) 55.0 (42) µm. Width (56) 47.6 (40) µm. Specimens = 64 (20).
Affinities:
Duxbury, 1980, p. 116: Diphasiosphaera stolidota:
This is a very distinctive species, particularly in the extent of its cavation and in the mode of attachment of the body layers. The parasutural processes, at their fullest development, are similar to those of some species of Spiniferites Mantell, 1850 emend. Sarjeant, 1970. Reduction of processes in the more cavate regions involves firstly the loss of process "stalks" so that one may see double rows of spines marking out paraplate boundaries with these spines representing the distal bifurcation of parasutural processes. Eventually, when the cavation reaches a sufficient extent, the double rows are reduced to nothing.
Harding, 1990, p.30: The variability of this species is marked and probably phenotypic. The apical prominence noted by Duxbury (1980) is an uncommon feature. This cyst type is common in the early Barremian of most sections studied (except for Speeton which may explain why Duxbury believed it to be restricted to the Cement Beds), disappearing in late Barremian time. The L-type ventral organisation of this species is the reason for placing it in this Cyst Complex, almost all of the Spiniferites Complex cysts have S-type ventral organisation.
Following the paratabulation patterns of Helenes (1986), the antapical region displays a symmetrical arrangement and the ventral region a l u/l i arrangement. The apical pattern has not been determined.
The type species of the genus, H. membraniphorum Ageloupolus 1964, differs from H. stolidota in having only hypocystal cavation. Whereas H. coninckii Heilmann-Clausen 1985 possesses an extremely large mid-ventral claustrum, that in H. stolidota is of much smaller dimensions, with paratabulation features clearly indicating it to be developed in a region equivalent to the site of flagellar insertion on the motile cell.
Originally Diphasiosphaera, subsequently (and now) Hystrichostrogylon.
Holotype: Duxbury, 1980, pl.1, fig. 5; text-fig.6
Locus typicus: Speeton Clay, Speeton, England
Stratum typicum: Barremian
--------------------------------------------------
G.L. Williams short notes on species, Mesozoic-Cenozoic dinocyst course, Urbino, Italy, May 17-22, 1999 - LPP VIEWER CD-ROM 99.5.
Hystrichostrogylon stolidotum (Duxbury, 1980) Stover and Williams, 1987, emend. Harding, 1990b. According to Harding (1990b, p.29), this species has an endocyst barely two-thirds the length of the pericyst and an apical prominence and projecting parasutural processes. Spiniferites type processes extend from parasutures and are of variable height depending on degree of cavation. In cases of extreme cavation, the process terminations only are developed along the parasutural ridges, appearing as a double row of processes. Cavation often complete but there may be contact between the two wall layers dorsally. Paratabulation L-type sexiform, archeopyle precingular, resulting from loss of 3". Ofter a periphragmal claustrum in flagellar scar region. Size: 65-95 x 59-92 µm.
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Original diagnosis: Duxbury, 1980, p.116: Diphasiosphaera stolidota
A cavate dinoflagellate cyst which is distinctly bi-layered and consists of a smooth, spheroidal endoblast and a smooth to finely perforate, spheroidal periblast. The periplast bears a distinct apical projection and has a large sulcal hole. Both body layers are characteristically extensively folded. Apparently typically gonyaulacacean paratabulation is outlined on the periblast by parasutural processes of varying height. The archeopyle is single-paraplate precingular (3"). Around the archeopyle margin, where the two body layers are appressed, the full development of fairly closely-spaced parasutural processes is seen and in this area, parasutural crests may proximally connect the processes. Away from the archeopyle margin and that part of the paracingulum directly posterior to it, the parasutural processes are reduced to a varying extent. As a rule, the greater the distance between the body layers, the shorter the parasutural processes, so that in the ventral area they may be reduced to nothing.
Observed Dimensions: Holotype 86x70 Ám. Overall 95(76)65x92(69)59 Ám.
Emended diagnosis: Harding, 1990, p.29
Shape: Ambitus elongate ovoidal, modified by rare development of apical prominence and projecting parasutural processes. Greatest width across paracingulum. Epicyst and hypocyst equal in length. Endocyst ambitus subcircular to ovoidal, barely two thirds the length of the pericyst. Slight dorso-ventral compression.
Phragma: Periphragm thin 0.3 Ám, with 'orange-peel' surface sculpture. Periphragmal claustrum developed in region of flagellar scar. Spiniferites-type processes extend distally from low ridges which delineate parasutures. The processes are of variable height depending on the degree of cavation. The greater the cavation the shorter the length of the process stalks. Processes bifurcate (or trifurcate if gonal) and may bifurcate again. In cases of extreme cavation the process terminations only are developed along the parasutural ridges, appearing as a double row of processes. Endophragm has a thick wall with a granular surface. Cavation is often complete, but there may be contact between the two wall layers dorsally.
Paratabulation: L-type sexiform gonyaulacoid. Paratabulation formula: 4', 6", 6c, 6''', 1'''', 1p, 5s.
Archaeopyle: Type P4/P4. Opercula both free, monoplacoid.
Paracingulum: In most cases difficult to determine due to collapse of cyst. No indentation in ambital view, laevorotatory, displaced by--2 cingulum widths.
Parasulcus: Periphragmal claustrum in flagellar scar region is often of a very large size (up to 18 µm X 18 µm), similar to that of the archaeopyle. L-type ventral paratabulation developed around this claustrum.
Dimensions: Length (62) 55.0 (42) µm. Width (56) 47.6 (40) µm. Specimens = 64 (20).
Affinities:
Duxbury, 1980, p. 116: Diphasiosphaera stolidota:
This is a very distinctive species, particularly in the extent of its cavation and in the mode of attachment of the body layers. The parasutural processes, at their fullest development, are similar to those of some species of Spiniferites Mantell, 1850 emend. Sarjeant, 1970. Reduction of processes in the more cavate regions involves firstly the loss of process "stalks" so that one may see double rows of spines marking out paraplate boundaries with these spines representing the distal bifurcation of parasutural processes. Eventually, when the cavation reaches a sufficient extent, the double rows are reduced to nothing.
Harding, 1990, p.30: The variability of this species is marked and probably phenotypic. The apical prominence noted by Duxbury (1980) is an uncommon feature. This cyst type is common in the early Barremian of most sections studied (except for Speeton which may explain why Duxbury believed it to be restricted to the Cement Beds), disappearing in late Barremian time. The L-type ventral organisation of this species is the reason for placing it in this Cyst Complex, almost all of the Spiniferites Complex cysts have S-type ventral organisation.
Following the paratabulation patterns of Helenes (1986), the antapical region displays a symmetrical arrangement and the ventral region a l u/l i arrangement. The apical pattern has not been determined.
The type species of the genus, H. membraniphorum Ageloupolus 1964, differs from H. stolidota in having only hypocystal cavation. Whereas H. coninckii Heilmann-Clausen 1985 possesses an extremely large mid-ventral claustrum, that in H. stolidota is of much smaller dimensions, with paratabulation features clearly indicating it to be developed in a region equivalent to the site of flagellar insertion on the motile cell.