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Diacanthum hollisteri
Diacanthum hollisteri Habib, 1972, p.376-377, pl.9, figs.1,3; pl.10, fig.1; text-fig.2. Emendation: Habib and Drugg, 1987, p.762, as Diacanthum hollisteri.
Originally (and now) Diacanthum, subsequently Occisucysta. Lentin and Williams (1981, p.80) retained this species in Diacanthum.
Taxonomic senior synonym: Gonyaulacysta (as and now Occisucysta) evittii, according to Below (1982a, p.32-33) - however, Jan du Chêne et al. (1986b, p.122) and Habib and Drugg (1987, p.762-763) retained Diacanthum hollisteri.
Holotype: Habib, 1972, pl.9, fig.1; Fensome et al., 1995, fig.1 - p.1547.
Locus typicus: DSDP Leg 11, Atlantic Ocean
Age: ?Valanginian.
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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.
Diacanthum hollisteri Habib, 1972, emend. Habib and Drugg, 1987, has the tabulation delineated by relatively high, perforate to vertically striate septa which define plate boundaries. Short blunt-tipped, conical spines occur in the intratabular areas. According to Habib and Drugg (1987, p.762), the archeopyle is most commonly formed from the loss of 2" and 3". Size: length 75-104 µm.
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Original description: Habib, 1972, p. 376-377
Proximate cysts compressed to a subcircular outline. Apical polar areas always well-rounded, and without horns. Periphragm and endophragm closely appressed. Cingulum is narrow, and only weakly helicoid, it divides the epitract and hypotract into more-or-less equal halves. Sulcus extends deeply into hypotract. Tabulation is that for the genus. Precingular archeopyle apparently formed by plates 3" and 4". Plate boundaries formed by raised crests which for the most part are perforate; the perforate crests do not appear to be entirely restricted to plate margins, as they extend over the periphragm, to varying degrees, as alveolae. Periphragm covered with dense grana, and by isolated broadly tapering sharp spines.
Size of twenty measured specimens from 75 to 104 µm, maximum length.
Emended description: Habib and Drugg, 1987, p. 762
Relatively large, spheroidal, proximate cysts which, when compressed, have an oval, subcircular, or elliptical outline, because of almost equidimensional shape, compressions may vary from lateral to dorsoventral to apical/antapical; outline largely controlled by arcuate lenticular compression folds which are concentrated near the periphery. Wall thin, less than 0.5 µm thick; it is densely perforate, and at least some of the perforations penetrate it completely. Discrete, short apical horn may be present, or there may instead be a rounded apical protubenance formed by the confluence of plate boundaries. Cingulum thin, and displaced approximately one cingulum-width adjacent the sulcus. Sulcus confined largely to hypocyst; hypocystal part characterized by medial linear splitting of the wall layer which extends from near the posterior end of the sulcus, from the posterior sulcal plate; to the approximation position of the intersection of the cingulum and the sulcus. Cyst tabulation expressed by relatively high, perforate to verocally striate, septa which define plate boundaries. Relatively short, blunt-tipped, conical spines cluster in the intratabular area; within a given plate, they may be joined at the base to form an intratabular ridge adjacent a septum; intratabular ridge may be straight or curved. Striations radiate from the base of each spine, giving the appearance on the surface of an uneven mosaic of spines, striations, and perforations which mask the thinness of the cyst wall itself. Cyst tabulation sexiform gonyaulacoid with l,type ventral organisation; formula pr, 4', 0a, 6'', Xc, 6''', 1p, 1'''', 4-5s. Epicystaltabulation characterized by a narrow sixth precingular plate (6'') which is subparallel to the adjacent, more-or-less straight sulcus, a correspondingly wide fifth precingular plate (5'') and a narrower but higher, attenuated trapezoidal to almost triangular first precingular plate (1'') The second (2'') and fourth (4'') precingular plates are trapezoidal, and lie on either side of the mid-dorsal, pentagonal, third (3'') precingular plate. Plate 2" is almost rectangular, and is larger than the almost square (quadrate) plate 4''. The apical series consists of a narrow, rectangular to slightly convexly bowed, first apical plate (1'), a hexagonal second apical plate (2'), and a pentagonal fourth apical plate (4') the three of which have a common juncture at the apex The apical horn, when discrete, arises from this juncture and may be flat-topped in the form of a small, pentagonal, preapical plate (pr.). In some cysts, the pr plate is divided by a raised partition. The third apical plate (3') is Pentagonal; it is displaced to the right and dorsal of the apex along the length of the common boundary between plates 2' and 4'. The hypocystal tabulation is characterized by a small first postcingular plate (1') which is always smaller than the first posterior intercalary plate (1p). The third plate (3''') curves under the 1p and second postcingular (2''') plates, and contacts the antapical plate without contacting the sulcus. The fourth postcingular plate (4''') is relatively small and rectangular. The fifth postcingular plate (5''') is large and curves under a small, semicircular, sixth postcingular plate (6'''). The single antapical plate (1''')is indented on the ventral side by contact with the sulcus; the right side of plate 1'''' is longer than its left side. Sulcal tabulation formula ps, Is, rs, ras, as. Commonly, the right anterior sulcal (ras) is absent, and the left sulcal (Is) and right sulcal (rs) plates lie on the side of the medial split. The posterior sulcal (ps) is rounded at its posterior end. The anterior sulcal (as) is narrow. Archeopyle is variable, in the loss of one, two or three precingular plates; formula P(3''), or 2P(2''-3''), or 2P(3''-4'') or 3(P2''-3''-4''). Most frequently, the second and third precingular plates form the archeopyle; Iess frequently, it corresponds to the third and fourth precingular plates or to the second, third, and fourth precingular plates; rarely, it is formed by the opening of the third precingular plate alone. In most cysts, the operculum is free; most frequently it is adherent to the cyst along the boundary with the cingulum or detached from the cyst but remaining closey associated to it. There may be one or two opercular pieces in those cysts with the 2P archeopyle. Size of the cysts varies from 75 to 105 µm in maximum dimensions.
Affinities: Habib and Drugg, 1987, p. 762-764 (annotated)
The emended description of Diacanthum hollisteri is based on the restudy of a large number of specimens from Sites 105 (Habib, 1972), 534 (Habib and Drugg, 1983) and 603, as well as from the European Tethyan stratotype and parastratotype sections of the Berriasian and Valanginian stages. The definition of D. hollisreri is revised to disclose details of cyst tabulation, variability of the archeopyle formula, close association and even adherence of the operculum to the cyst in many specimens in a given assemblage, and variation in the number of opercular pieces. The species is distinguished further by its rotund appearance in those compressed specimens that are largely devoid of compression folds, and by the medial linear splitting of the sulcus which can be detected in appropriately oriented, well-preserved, specimens.
The morphology of D. hollisteri is similar to that of Occisucysta evittii (Dodekova) Gitmez and to species of Cribroperidinium such as C. conjunctum (Eisenack and Cookson) Helenes. In O. evittii, C. conjunctum, and D. hollisteri hypocystal plate 5''' is large and epicystal 5'' is wide, especially when compared with epicystal 6''. Also epicystal 6'' is intercalated between apical plates 1' and 4' in the three species. In addition, although both epicystal plate 2'' and 4'' are trapezoidal, the former appears always to be larger than the latter. The species are similar also with respect to the L-type ventral tabulation of the cyst, sexiform organization of hypocystal tabulation, and presence of low-lying, spinate, intratabular ridges. D. hollisleri is also similar to Diacanlhum filapicalum (Gocht) Stover and Evitt. The species apparently share the basic cribroperidinioid plate geometry given above. In addition, both species are perforate and possess intratabular spines (although D. filapicalum apparently does not possess intratabular ridges), and in both species, for example, Gocht, 1970, pl. 27, fig. 2, there are examples of a medial splitting of the sulcus which extends from the posterior sulcal plate to the level of the cingulum. However, D. filapicalum differs from D. hollisleri by the presence of two small Plates intercalated near the precingular margins of apical plates 2' and 3' and by the apparently common juncture of all apical plates at the apex (Gocht, 1970, p. 134, fig. 4).
The single feature which distinguishes D. hollisleri collectively from the three species with which it is compared is the variability of the excystment apparatus. The extent of archeopyle variability is from P(3'') to 2P(2''-3'') to 2P(3''-4'') to 3P(2''-3''-4''). In several cysts, the archeopyIe is 2P(2''-3''), with sutures (not septa) partially dehiscing also along the adjacent fourth precingular plate. The operculum may remain adherent at the cingulum, or laterally against adjacent percingular plates. Opereula which are detached from the cyst but remain close to the archeopyle are considered to have been originally adherent, but became detached at some stage during sample preparation.
Otherwise it is difficult to envision how an operculum can be completely disconnected from the cyst but remain so closely associated to it through the processes of excystment and/or sedimentation. The operculum may consist of one or two pieces.
In Cribroperidinium, the archeopyle is always P3(3''), and the operculum is free, although there are species in which the operculum is adherent (Helenes, 1984). In Occisucysta, the archeopyl is 2P(2''-3''). According to the description of O. evittii, given by Dodekova, 1969, all specimens that were examined contained the fully developed archeopyle. In specimens that were attributed to O. evittii by Below (1982), the operculum is free and consists of two opercular pieces. Below (1982) also illustrated a specimen with the P(2'') archeopyle. In D. filapicalum, the archeopyle is 2P(3''-4''). Gocht (1970) illustrated a specimen he designated the holotype with the P3('') plate completely detached and the P(4'') plate partially detachd. There are a number of species in sections of Middle Jurassic to Early Cretaceous age which resemble D. hollisleri in the possession of Cribroperidinium-like tabulation, spinate intratabular ridges, and perforate cyst wall. Detailed examination which takes into account the varjability which may occur in fossil populations may reveal the taxonomic and phylogenetic relationships of these taxa. Nevertheless, D. hollisleri is a valuable guide species (and is stratigraphically important) in the Berriasian-Valanginian Tethyan western North Atlantic (and adjacent Gulf of Mexico; Riley and Fenton, 1984) and Tethyan submediterranean European stratotyp and parastratotyp sections of he Berriasian and the Valanginian. It is a species which is apparently absent or rare in the Boreal province. This species should not be confused with the species from the Early Cretaceous of Morocco which Below (1982) considered to be the senior synonym of D. hollisleri.
Originally (and now) Diacanthum, subsequently Occisucysta. Lentin and Williams (1981, p.80) retained this species in Diacanthum.
Taxonomic senior synonym: Gonyaulacysta (as and now Occisucysta) evittii, according to Below (1982a, p.32-33) - however, Jan du Chêne et al. (1986b, p.122) and Habib and Drugg (1987, p.762-763) retained Diacanthum hollisteri.
Holotype: Habib, 1972, pl.9, fig.1; Fensome et al., 1995, fig.1 - p.1547.
Locus typicus: DSDP Leg 11, Atlantic Ocean
Age: ?Valanginian.
--------------------------------------------------
G.L. Williams short notes on species, Mesozoic-Cenozoic dinocyst course, Urbino, Italy, May 17-22, 1999 - LPP VIEWER CD-ROM 99.5.
Diacanthum hollisteri Habib, 1972, emend. Habib and Drugg, 1987, has the tabulation delineated by relatively high, perforate to vertically striate septa which define plate boundaries. Short blunt-tipped, conical spines occur in the intratabular areas. According to Habib and Drugg (1987, p.762), the archeopyle is most commonly formed from the loss of 2" and 3". Size: length 75-104 µm.
--------------------------------------------------
Original description: Habib, 1972, p. 376-377
Proximate cysts compressed to a subcircular outline. Apical polar areas always well-rounded, and without horns. Periphragm and endophragm closely appressed. Cingulum is narrow, and only weakly helicoid, it divides the epitract and hypotract into more-or-less equal halves. Sulcus extends deeply into hypotract. Tabulation is that for the genus. Precingular archeopyle apparently formed by plates 3" and 4". Plate boundaries formed by raised crests which for the most part are perforate; the perforate crests do not appear to be entirely restricted to plate margins, as they extend over the periphragm, to varying degrees, as alveolae. Periphragm covered with dense grana, and by isolated broadly tapering sharp spines.
Size of twenty measured specimens from 75 to 104 µm, maximum length.
Emended description: Habib and Drugg, 1987, p. 762
Relatively large, spheroidal, proximate cysts which, when compressed, have an oval, subcircular, or elliptical outline, because of almost equidimensional shape, compressions may vary from lateral to dorsoventral to apical/antapical; outline largely controlled by arcuate lenticular compression folds which are concentrated near the periphery. Wall thin, less than 0.5 µm thick; it is densely perforate, and at least some of the perforations penetrate it completely. Discrete, short apical horn may be present, or there may instead be a rounded apical protubenance formed by the confluence of plate boundaries. Cingulum thin, and displaced approximately one cingulum-width adjacent the sulcus. Sulcus confined largely to hypocyst; hypocystal part characterized by medial linear splitting of the wall layer which extends from near the posterior end of the sulcus, from the posterior sulcal plate; to the approximation position of the intersection of the cingulum and the sulcus. Cyst tabulation expressed by relatively high, perforate to verocally striate, septa which define plate boundaries. Relatively short, blunt-tipped, conical spines cluster in the intratabular area; within a given plate, they may be joined at the base to form an intratabular ridge adjacent a septum; intratabular ridge may be straight or curved. Striations radiate from the base of each spine, giving the appearance on the surface of an uneven mosaic of spines, striations, and perforations which mask the thinness of the cyst wall itself. Cyst tabulation sexiform gonyaulacoid with l,type ventral organisation; formula pr, 4', 0a, 6'', Xc, 6''', 1p, 1'''', 4-5s. Epicystaltabulation characterized by a narrow sixth precingular plate (6'') which is subparallel to the adjacent, more-or-less straight sulcus, a correspondingly wide fifth precingular plate (5'') and a narrower but higher, attenuated trapezoidal to almost triangular first precingular plate (1'') The second (2'') and fourth (4'') precingular plates are trapezoidal, and lie on either side of the mid-dorsal, pentagonal, third (3'') precingular plate. Plate 2" is almost rectangular, and is larger than the almost square (quadrate) plate 4''. The apical series consists of a narrow, rectangular to slightly convexly bowed, first apical plate (1'), a hexagonal second apical plate (2'), and a pentagonal fourth apical plate (4') the three of which have a common juncture at the apex The apical horn, when discrete, arises from this juncture and may be flat-topped in the form of a small, pentagonal, preapical plate (pr.). In some cysts, the pr plate is divided by a raised partition. The third apical plate (3') is Pentagonal; it is displaced to the right and dorsal of the apex along the length of the common boundary between plates 2' and 4'. The hypocystal tabulation is characterized by a small first postcingular plate (1') which is always smaller than the first posterior intercalary plate (1p). The third plate (3''') curves under the 1p and second postcingular (2''') plates, and contacts the antapical plate without contacting the sulcus. The fourth postcingular plate (4''') is relatively small and rectangular. The fifth postcingular plate (5''') is large and curves under a small, semicircular, sixth postcingular plate (6'''). The single antapical plate (1''')is indented on the ventral side by contact with the sulcus; the right side of plate 1'''' is longer than its left side. Sulcal tabulation formula ps, Is, rs, ras, as. Commonly, the right anterior sulcal (ras) is absent, and the left sulcal (Is) and right sulcal (rs) plates lie on the side of the medial split. The posterior sulcal (ps) is rounded at its posterior end. The anterior sulcal (as) is narrow. Archeopyle is variable, in the loss of one, two or three precingular plates; formula P(3''), or 2P(2''-3''), or 2P(3''-4'') or 3(P2''-3''-4''). Most frequently, the second and third precingular plates form the archeopyle; Iess frequently, it corresponds to the third and fourth precingular plates or to the second, third, and fourth precingular plates; rarely, it is formed by the opening of the third precingular plate alone. In most cysts, the operculum is free; most frequently it is adherent to the cyst along the boundary with the cingulum or detached from the cyst but remaining closey associated to it. There may be one or two opercular pieces in those cysts with the 2P archeopyle. Size of the cysts varies from 75 to 105 µm in maximum dimensions.
Affinities: Habib and Drugg, 1987, p. 762-764 (annotated)
The emended description of Diacanthum hollisteri is based on the restudy of a large number of specimens from Sites 105 (Habib, 1972), 534 (Habib and Drugg, 1983) and 603, as well as from the European Tethyan stratotype and parastratotype sections of the Berriasian and Valanginian stages. The definition of D. hollisreri is revised to disclose details of cyst tabulation, variability of the archeopyle formula, close association and even adherence of the operculum to the cyst in many specimens in a given assemblage, and variation in the number of opercular pieces. The species is distinguished further by its rotund appearance in those compressed specimens that are largely devoid of compression folds, and by the medial linear splitting of the sulcus which can be detected in appropriately oriented, well-preserved, specimens.
The morphology of D. hollisteri is similar to that of Occisucysta evittii (Dodekova) Gitmez and to species of Cribroperidinium such as C. conjunctum (Eisenack and Cookson) Helenes. In O. evittii, C. conjunctum, and D. hollisteri hypocystal plate 5''' is large and epicystal 5'' is wide, especially when compared with epicystal 6''. Also epicystal 6'' is intercalated between apical plates 1' and 4' in the three species. In addition, although both epicystal plate 2'' and 4'' are trapezoidal, the former appears always to be larger than the latter. The species are similar also with respect to the L-type ventral tabulation of the cyst, sexiform organization of hypocystal tabulation, and presence of low-lying, spinate, intratabular ridges. D. hollisleri is also similar to Diacanlhum filapicalum (Gocht) Stover and Evitt. The species apparently share the basic cribroperidinioid plate geometry given above. In addition, both species are perforate and possess intratabular spines (although D. filapicalum apparently does not possess intratabular ridges), and in both species, for example, Gocht, 1970, pl. 27, fig. 2, there are examples of a medial splitting of the sulcus which extends from the posterior sulcal plate to the level of the cingulum. However, D. filapicalum differs from D. hollisleri by the presence of two small Plates intercalated near the precingular margins of apical plates 2' and 3' and by the apparently common juncture of all apical plates at the apex (Gocht, 1970, p. 134, fig. 4).
The single feature which distinguishes D. hollisleri collectively from the three species with which it is compared is the variability of the excystment apparatus. The extent of archeopyle variability is from P(3'') to 2P(2''-3'') to 2P(3''-4'') to 3P(2''-3''-4''). In several cysts, the archeopyIe is 2P(2''-3''), with sutures (not septa) partially dehiscing also along the adjacent fourth precingular plate. The operculum may remain adherent at the cingulum, or laterally against adjacent percingular plates. Opereula which are detached from the cyst but remain close to the archeopyle are considered to have been originally adherent, but became detached at some stage during sample preparation.
Otherwise it is difficult to envision how an operculum can be completely disconnected from the cyst but remain so closely associated to it through the processes of excystment and/or sedimentation. The operculum may consist of one or two pieces.
In Cribroperidinium, the archeopyle is always P3(3''), and the operculum is free, although there are species in which the operculum is adherent (Helenes, 1984). In Occisucysta, the archeopyl is 2P(2''-3''). According to the description of O. evittii, given by Dodekova, 1969, all specimens that were examined contained the fully developed archeopyle. In specimens that were attributed to O. evittii by Below (1982), the operculum is free and consists of two opercular pieces. Below (1982) also illustrated a specimen with the P(2'') archeopyle. In D. filapicalum, the archeopyle is 2P(3''-4''). Gocht (1970) illustrated a specimen he designated the holotype with the P3('') plate completely detached and the P(4'') plate partially detachd. There are a number of species in sections of Middle Jurassic to Early Cretaceous age which resemble D. hollisleri in the possession of Cribroperidinium-like tabulation, spinate intratabular ridges, and perforate cyst wall. Detailed examination which takes into account the varjability which may occur in fossil populations may reveal the taxonomic and phylogenetic relationships of these taxa. Nevertheless, D. hollisleri is a valuable guide species (and is stratigraphically important) in the Berriasian-Valanginian Tethyan western North Atlantic (and adjacent Gulf of Mexico; Riley and Fenton, 1984) and Tethyan submediterranean European stratotyp and parastratotyp sections of he Berriasian and the Valanginian. It is a species which is apparently absent or rare in the Boreal province. This species should not be confused with the species from the Early Cretaceous of Morocco which Below (1982) considered to be the senior synonym of D. hollisleri.