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Heslertonia
From Fensome et al., 2019:
Heslertonia, Sarjeant, 1966b, p.133.
Emendation: Duxbury, 1980, p.123.
Type: Neale and Sarjeant, 1962, pl.19, fig.5; text-fig.1, as Gonyaulax heslertonensis.
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Original description: [Sarjeant, 1966]:
Diagnosis:
Chorate dinoflagellate cyst, spherical, ellipsoidal, ovoidal or polyhedral, with high sutural crests outlining the tabulation 3-4`, 0-1a, 6``, 6c, 6```, 1p, 0-1pv, 1````. Cingulum strongly or weakly helicoid; sulcus generally but not constantly extending on to epitract. Apical and antapical horns absent. Sutures perforate or imperforate; their distal edges smooth or denticulate. Crest height exceeds 1/4 of shell width. Surface smooth, granular, punctate, nodose or reticulate. Precingular archaeopyle formed by loss of plate 3``; archaeopyle sometimes absent.
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Modified description:
Stover and Evitt 1978, p. 160-161:
Synopsis:
Cysts proximochorate; body subspherical; paratabulation gonyaulacacean, indicated by high parasutural septa, height of which is greater than one-fourth main body diameter; archeopyle precingular, Type P.
Description:
Shape: Body subspherical.
Wall relationships: Autophragm only.
Wall features: Parasutural septa high, height greater than one-fourth main body diameter; smooth, perforate or imperforate, with finely denticulate or smooth distal margins. Autophragm between septa smooth or variously ornamented with features of low relief.
Paratabulation: Indicated by parasutural septa; gonyaulacacean, formula: 4`, 0-1a, 6``, 6c, 6```, 1p, 1````, 1s.
Archeopyle: Precingular, Type P (3`` only); operculum free.
Paracingulum: Indicated by six paraplates.
Parasulcus: Expressed as a narrow longitudinally elongate area, mainly on hypocyst, bordered by parasutural septa.
Size: Small to intermediate
Affinities:
On Heslertonia the height of the parasutural features is >0.25 of body diameter; whereas on Impagidinium and Leptodinium, the height is <0.25 of body diameter. A better understanding of paratabulation details on Heslertonia and Pterodinium - as well as on possible transitional forms not too unlike Spiniferites cingulatus and S. pterotus - may eventually justify the suppression on Heslertonia.
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Emended description:
Duxbury, 1980:
Diagnosis:
Spheroidal to ovoidal dinoflagellate cysts bearing high, regular parasutural crests outlining a typically gonyaulacacean paratabulation pattern. The crests are higher than 1/4 the main body diameter and may vary in height on individual specimens. The main body surface is smooth to finely granular and the archeopyle is epicystal.
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Heslertonia Sarjeant 1966b, p. 133
Dimidium Pearce 2010, p. 56
Type: Neale and Sarjeant 1962, pl. 19, fig. 5; text-fig. 1, as Gonyaulax heslertonensis
Emended Diagnosis: Spheroidal to ovoidal dinoflagellate cysts of moderate size bearing sutural crests outlining a typically gonyaulacacean tabulation pattern; the crests may vary in height between species and on individual specimens. There is no apical projection. The main body surface is smooth, finely granular, rugulate or reticulate and the archeopyle is epicystal.
Remarks: The original diagnosis of this genus (Sarjeant 1966b, p. 133) was emended by Duxbury (1980, p. 123) essentially to emphasise the epicystal archeopyle. It is further emended here in light of more recent studies to encompass the rugulate H. senecta Harding 1990 ex Harding in Williams et al. 1998 and the reticulate Heslertonia reticulata Duxbury 2023. Crestal height has now been shown as very variable between species, being reduced in Heslertonia inferior n. sp. and H. reticulata, certainly lower than, "¼ the main body diameter", as specified by Sarjeant 1966b and Duxbury 1980. In discussing his genus Dimidium, Pearce (2010, p. 57) stated that, "Dimidium most closely resembles Heslertonia Sarjeant, 1966 but differs in possessing parasutural crests that are much lower than ¼ body width". The very low crest height of his material is atypical when compared to Clarke and Verdier's type material for their Gonyaulacysta striata. Pearce recognised this in stating (op. cit., p. 60), "it is clear the crest heights of Dimidium striatum from the Trunch borehole are lower than those from the type material of Clarke and Verdier". Pearce (op. cit., p. 57, 60) combined Yun's (1981) species Heslertonia regula and Gonyaulacysta striata Clarke and Verdier 1967 into Dimidium striatum (Clarke and Verdier 1967) Pearce 2010. He recognised, however, that for H. regula "The average maximum crest height…is less than ¼ the average shortest body dimension…( although only just exceeds that in the holotype)" and that the maximum crest height of Yun’s P. striatum specimens exceeded ¼ of the largest body dimension. Pearce thus contradicted his stipulation that sutural crest height should be "much lower than ¼ body width" in Dimidium.
Dimidium Pearce 2010 is included in Heslertonia here, honouring the diagnosis of Heslertonia as emended above to include such low-crested species as Heslertonia inferior n. sp. and H. reticulata Duxbury 2023. This is in agreement with Pearce's own assertion (op. cit., p. 57), "Ornamentation height (i.e. processes or crests) is probably an unsuitable generic level discriminator" and follows Yun's lead in his assignment of Heslertonia regula to that genus. The last species is considered a synonym of Heslertonia striata (Eisenack and Cookson 1960) n. comb. Sarjeant (1966b, p. 133) compared the type species, Heslertonia heslertonensis (Neale and Sarjeant 1962) Sarjeant 1966b to Cymatiosphaera striata Eisenack and Cookson 1960 (transferred to Heslertonia in Norvick 1975), stating that "both forms have in common high, striate crests" and suggesting that if these taxa were congeneric or conspecific, "the earlier name striata would have priority". Despite this, Norvick (1975, p.47), in re-assigning Cymatiosphaera striata to Heslertonia, stated that H. heslertonensis, "differs slightly from the Australian species in having branched and non-striate lists". Norvik (op. cit.) also stated that in H. striata, "A precingular, haplotabular archaeopyle is sometimes developed", and the specimen figured in Norvik 1975, pl. 10, fig. 10 does appear to show a single- plate precingular archeopyle, which is a key criterion excluding "Cymatiosphaera striata" from Heslertonia. Neale and Sarjeant (1962, p. 441) and Norvik (1975, p. 47) both assumed H. heslertonense to have a precingular archeopyle. Neale and Sarjeant (op. cit.) stated, "A resemblance exists to the genus Pterodinium Eisenack 1958, which also has high crests" and Norvick (1975, p. 47) transferred Cymatiosphaera striata to Heslertonia because of, "The presence of tabulation, the high sutural lists and the precingular archaeopyle". Although Norvik recognised that some forms of Pterodinium bear high sutural lists, he felt that, "these were never as well-developed as in Heslertonia striata". However, in his emendation of Pterodinium, Sarjeant (1975, p. 71) specified crestal height as, "in the range 20-30% of the central body breadth", and the specimen of "Heslertonia striata" illustrated by Norvick (op. cit., pl.10, fig. 10) falls within that range. Cymatiosphaera striata is re-assigned to Pterodinium below.
Heslertonia, Sarjeant, 1966b, p.133.
Emendation: Duxbury, 1980, p.123.
Type: Neale and Sarjeant, 1962, pl.19, fig.5; text-fig.1, as Gonyaulax heslertonensis.
---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
Original description: [Sarjeant, 1966]:
Diagnosis:
Chorate dinoflagellate cyst, spherical, ellipsoidal, ovoidal or polyhedral, with high sutural crests outlining the tabulation 3-4`, 0-1a, 6``, 6c, 6```, 1p, 0-1pv, 1````. Cingulum strongly or weakly helicoid; sulcus generally but not constantly extending on to epitract. Apical and antapical horns absent. Sutures perforate or imperforate; their distal edges smooth or denticulate. Crest height exceeds 1/4 of shell width. Surface smooth, granular, punctate, nodose or reticulate. Precingular archaeopyle formed by loss of plate 3``; archaeopyle sometimes absent.
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Modified description:
Stover and Evitt 1978, p. 160-161:
Synopsis:
Cysts proximochorate; body subspherical; paratabulation gonyaulacacean, indicated by high parasutural septa, height of which is greater than one-fourth main body diameter; archeopyle precingular, Type P.
Description:
Shape: Body subspherical.
Wall relationships: Autophragm only.
Wall features: Parasutural septa high, height greater than one-fourth main body diameter; smooth, perforate or imperforate, with finely denticulate or smooth distal margins. Autophragm between septa smooth or variously ornamented with features of low relief.
Paratabulation: Indicated by parasutural septa; gonyaulacacean, formula: 4`, 0-1a, 6``, 6c, 6```, 1p, 1````, 1s.
Archeopyle: Precingular, Type P (3`` only); operculum free.
Paracingulum: Indicated by six paraplates.
Parasulcus: Expressed as a narrow longitudinally elongate area, mainly on hypocyst, bordered by parasutural septa.
Size: Small to intermediate
Affinities:
On Heslertonia the height of the parasutural features is >0.25 of body diameter; whereas on Impagidinium and Leptodinium, the height is <0.25 of body diameter. A better understanding of paratabulation details on Heslertonia and Pterodinium - as well as on possible transitional forms not too unlike Spiniferites cingulatus and S. pterotus - may eventually justify the suppression on Heslertonia.
-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
Emended description:
Duxbury, 1980:
Diagnosis:
Spheroidal to ovoidal dinoflagellate cysts bearing high, regular parasutural crests outlining a typically gonyaulacacean paratabulation pattern. The crests are higher than 1/4 the main body diameter and may vary in height on individual specimens. The main body surface is smooth to finely granular and the archeopyle is epicystal.
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Heslertonia Sarjeant 1966b, p. 133
Dimidium Pearce 2010, p. 56
Type: Neale and Sarjeant 1962, pl. 19, fig. 5; text-fig. 1, as Gonyaulax heslertonensis
Emended Diagnosis: Spheroidal to ovoidal dinoflagellate cysts of moderate size bearing sutural crests outlining a typically gonyaulacacean tabulation pattern; the crests may vary in height between species and on individual specimens. There is no apical projection. The main body surface is smooth, finely granular, rugulate or reticulate and the archeopyle is epicystal.
Remarks: The original diagnosis of this genus (Sarjeant 1966b, p. 133) was emended by Duxbury (1980, p. 123) essentially to emphasise the epicystal archeopyle. It is further emended here in light of more recent studies to encompass the rugulate H. senecta Harding 1990 ex Harding in Williams et al. 1998 and the reticulate Heslertonia reticulata Duxbury 2023. Crestal height has now been shown as very variable between species, being reduced in Heslertonia inferior n. sp. and H. reticulata, certainly lower than, "¼ the main body diameter", as specified by Sarjeant 1966b and Duxbury 1980. In discussing his genus Dimidium, Pearce (2010, p. 57) stated that, "Dimidium most closely resembles Heslertonia Sarjeant, 1966 but differs in possessing parasutural crests that are much lower than ¼ body width". The very low crest height of his material is atypical when compared to Clarke and Verdier's type material for their Gonyaulacysta striata. Pearce recognised this in stating (op. cit., p. 60), "it is clear the crest heights of Dimidium striatum from the Trunch borehole are lower than those from the type material of Clarke and Verdier". Pearce (op. cit., p. 57, 60) combined Yun's (1981) species Heslertonia regula and Gonyaulacysta striata Clarke and Verdier 1967 into Dimidium striatum (Clarke and Verdier 1967) Pearce 2010. He recognised, however, that for H. regula "The average maximum crest height…is less than ¼ the average shortest body dimension…( although only just exceeds that in the holotype)" and that the maximum crest height of Yun’s P. striatum specimens exceeded ¼ of the largest body dimension. Pearce thus contradicted his stipulation that sutural crest height should be "much lower than ¼ body width" in Dimidium.
Dimidium Pearce 2010 is included in Heslertonia here, honouring the diagnosis of Heslertonia as emended above to include such low-crested species as Heslertonia inferior n. sp. and H. reticulata Duxbury 2023. This is in agreement with Pearce's own assertion (op. cit., p. 57), "Ornamentation height (i.e. processes or crests) is probably an unsuitable generic level discriminator" and follows Yun's lead in his assignment of Heslertonia regula to that genus. The last species is considered a synonym of Heslertonia striata (Eisenack and Cookson 1960) n. comb. Sarjeant (1966b, p. 133) compared the type species, Heslertonia heslertonensis (Neale and Sarjeant 1962) Sarjeant 1966b to Cymatiosphaera striata Eisenack and Cookson 1960 (transferred to Heslertonia in Norvick 1975), stating that "both forms have in common high, striate crests" and suggesting that if these taxa were congeneric or conspecific, "the earlier name striata would have priority". Despite this, Norvick (1975, p.47), in re-assigning Cymatiosphaera striata to Heslertonia, stated that H. heslertonensis, "differs slightly from the Australian species in having branched and non-striate lists". Norvik (op. cit.) also stated that in H. striata, "A precingular, haplotabular archaeopyle is sometimes developed", and the specimen figured in Norvik 1975, pl. 10, fig. 10 does appear to show a single- plate precingular archeopyle, which is a key criterion excluding "Cymatiosphaera striata" from Heslertonia. Neale and Sarjeant (1962, p. 441) and Norvik (1975, p. 47) both assumed H. heslertonense to have a precingular archeopyle. Neale and Sarjeant (op. cit.) stated, "A resemblance exists to the genus Pterodinium Eisenack 1958, which also has high crests" and Norvick (1975, p. 47) transferred Cymatiosphaera striata to Heslertonia because of, "The presence of tabulation, the high sutural lists and the precingular archaeopyle". Although Norvik recognised that some forms of Pterodinium bear high sutural lists, he felt that, "these were never as well-developed as in Heslertonia striata". However, in his emendation of Pterodinium, Sarjeant (1975, p. 71) specified crestal height as, "in the range 20-30% of the central body breadth", and the specimen of "Heslertonia striata" illustrated by Norvick (op. cit., pl.10, fig. 10) falls within that range. Cymatiosphaera striata is re-assigned to Pterodinium below.