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Elimatia
From Fensome et al., 2019:
Elimatia, Duxbury, 2019, p.189–190.
Type: Davey, 1974, pl.7, figs.2–3, as Trichodinium speetonense.
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Original description Duxbury, 2019:
Derivation of Name: From the Latin elimatus, finished, elaborated, adorned – in reference to the characteristic spines. Diagnosis: Spheroidal to ovoidal dinocysts, autophragm only. Surface fibroreticulate and produced into short, acuminate spinules which are evenly distributed or which can be reduced or absent in “bald” areas. Tabulation is absent or partly outlined by aligned spinules and/or occasional very low ridges. Sulcal area sometimes less-densely spinose with a pronounced flagellar scar. An apical structure can be present, usually formed by fused clusters of longer spinules. Archeopyle single-plate precingular (presumed 3'').
Remarks: This genus has been described in order to accommodate species previously included in Trichodinium Eisenack and Cookson 1960 emend. Clarke and Verdier 1967, but which vary significantly from the type species T. pellitum Eisenack and Cookson 1960. As described and illustrated in Eisenack and Cookson (1960, p. 5, 6 and Plate 2, Figures 4 - 7), the genus Trichodinium included three significantly different morphotypes, connected only by characteristics broadly applicable to a number of genera. This was partially addressed by Clarke and Verdier (1967, p. 18, 19), who’s emendation specified only a precingular archeopyle, sculpture of, “generally short hairs, spines or small flat-topped processes” and a small apical horn. The latter authors contrasted Trichodinium with Apteodinium in its apical horn type, “commonly formed by the coalescence of several hairs or bristles in the apical region”, and in its “type of sculpture”. Although he did not formally address this issue, Morgan (1980, p.33) did recognise the need to reconsider Trichodinium after re-examination of the holotype of the type species, T. pellitum. Morgan (op. cit.) stated that, “the holotype and other specimens seen have a dense cover of intratabular hairs, with bare parasutural areas”; this is significantly at variance with most species included in this genus to date. Morgan (op. cit.) also pointed out that Trichodinium paucispinum Eisenack and Cookson 1960, has “a two plate precingular archeopyle, and the few spines appear to be parasutural”. The last species was transferred to Pervosphaeridium Yun Hyesu 1981 by Jan du Chêne et al. (1986a).
In the present study and following the observations of Morgan (1980, p. 33), T. pellitum, the type species of Trichodinium (Eisenack and Cookson 1960, Plate 2, Figure 4), is recognised as markedly different from several taxa previously included in that genus; these taxa have been transferred to Elimatia Duxbury n. gen. No comprehensive treatment is attempted here of several other species which still remain in Trichodinium (see Williams et al. 2017), although it is possible that Trichodinium might be monotypic considering the very distinctive characteristics of T. pellitum.
The third species described by Eisenack and Cookson (op. cit.), Trichodinium intermedium, was synonymised with Trichodinium castanea, by implication in Clarke and Verdier (1967, p.19), although this was rejected by Morgan (1980, p. 33), and Morgan (op. cit.) is followed here. Of Eisenack and Cookson’s three original morphotypes, T. intermedium is the only one here transferred to Elimatia n. gen.
The type material for Trichodinium castanea Deflandre 1935 ex Clarke and Verdier 1967 was from a ?Senonian flint erratic, and the published range covers much of the Cretaceous. Other species unquestionably included in Elimatia here are, however, all typical of Lower Cretaceous sediments. Because of this discrepancy, pending further review, T. castanea has not been transferred to Elimatia here.
Harding (1990, p. 37–39) introduced the concept of “true” and “false” apical horns in his treatment of four species of Trichodinium, T. calvus Harding 1990, T. ciliatum (Gocht 1959) Eisenack and Klement 1964, T. discus Harding 1990 and T. speetonense Davey 1974. Although Harding didn’t define “true” and “false”, the first appears to be similar to that displayed by several species of Cribroperidinium and Apteodinium whereas “false” horns are formed by apical tufts of particularly long spinules, which can be fused to varying degrees.
Trichodinium calvus appears to be the only species of this type with a “true” horn and is possibly a taxonomic junior synonym of Apteodinium? albertii Lentin and Williams 1981. In his description of A.? albertii (as Pareodinia spinosa), Alberti (1961, p. 24) refers to a pointed apical horn and very small surface spines 1.5 to 2 μm long, and his illustration (op. cit. Plate 4, Figure 16) suggests some reduction of this ornament on the epicyst; Alberti’s material was of a late Barremian age. All of these features closely match Harding’s (1990, p. 37) observations on T. calvus, also from the late Barremian.
In the present study, Trichodinium ciliatum, T. discus and T. speetonense are all readily transferred to Elimatia. Trichodinium calvus is also transferred to that genus, as Elimatia albertii (Lentin and Williams 1981) n. comb., although recognising that its “true” apical horn is atypical (see Plate 12, Figures 5, 7).
Duxbury (1980, p. 122, 123) described the “Trichodinium-type” body ornament of Cribroperidinium comptum (Duxbury) Stover and Evitt 1978, and this has been confirmed in the current study, together with the possession in some specimens of a tapering, “true” apical horn, very similar to that of Elimatia albertii (compare Plate 12, Figures 1, 5, 7). The LAD of C. comptum was at 27.05 m in Heslerton No. 2 and its range overlaps the late Barremian inception of E. albertii, allowing a possible linking of the two species.
Elimatia, Duxbury, 2019, p.189–190.
Type: Davey, 1974, pl.7, figs.2–3, as Trichodinium speetonense.
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Original description Duxbury, 2019:
Derivation of Name: From the Latin elimatus, finished, elaborated, adorned – in reference to the characteristic spines. Diagnosis: Spheroidal to ovoidal dinocysts, autophragm only. Surface fibroreticulate and produced into short, acuminate spinules which are evenly distributed or which can be reduced or absent in “bald” areas. Tabulation is absent or partly outlined by aligned spinules and/or occasional very low ridges. Sulcal area sometimes less-densely spinose with a pronounced flagellar scar. An apical structure can be present, usually formed by fused clusters of longer spinules. Archeopyle single-plate precingular (presumed 3'').
Remarks: This genus has been described in order to accommodate species previously included in Trichodinium Eisenack and Cookson 1960 emend. Clarke and Verdier 1967, but which vary significantly from the type species T. pellitum Eisenack and Cookson 1960. As described and illustrated in Eisenack and Cookson (1960, p. 5, 6 and Plate 2, Figures 4 - 7), the genus Trichodinium included three significantly different morphotypes, connected only by characteristics broadly applicable to a number of genera. This was partially addressed by Clarke and Verdier (1967, p. 18, 19), who’s emendation specified only a precingular archeopyle, sculpture of, “generally short hairs, spines or small flat-topped processes” and a small apical horn. The latter authors contrasted Trichodinium with Apteodinium in its apical horn type, “commonly formed by the coalescence of several hairs or bristles in the apical region”, and in its “type of sculpture”. Although he did not formally address this issue, Morgan (1980, p.33) did recognise the need to reconsider Trichodinium after re-examination of the holotype of the type species, T. pellitum. Morgan (op. cit.) stated that, “the holotype and other specimens seen have a dense cover of intratabular hairs, with bare parasutural areas”; this is significantly at variance with most species included in this genus to date. Morgan (op. cit.) also pointed out that Trichodinium paucispinum Eisenack and Cookson 1960, has “a two plate precingular archeopyle, and the few spines appear to be parasutural”. The last species was transferred to Pervosphaeridium Yun Hyesu 1981 by Jan du Chêne et al. (1986a).
In the present study and following the observations of Morgan (1980, p. 33), T. pellitum, the type species of Trichodinium (Eisenack and Cookson 1960, Plate 2, Figure 4), is recognised as markedly different from several taxa previously included in that genus; these taxa have been transferred to Elimatia Duxbury n. gen. No comprehensive treatment is attempted here of several other species which still remain in Trichodinium (see Williams et al. 2017), although it is possible that Trichodinium might be monotypic considering the very distinctive characteristics of T. pellitum.
The third species described by Eisenack and Cookson (op. cit.), Trichodinium intermedium, was synonymised with Trichodinium castanea, by implication in Clarke and Verdier (1967, p.19), although this was rejected by Morgan (1980, p. 33), and Morgan (op. cit.) is followed here. Of Eisenack and Cookson’s three original morphotypes, T. intermedium is the only one here transferred to Elimatia n. gen.
The type material for Trichodinium castanea Deflandre 1935 ex Clarke and Verdier 1967 was from a ?Senonian flint erratic, and the published range covers much of the Cretaceous. Other species unquestionably included in Elimatia here are, however, all typical of Lower Cretaceous sediments. Because of this discrepancy, pending further review, T. castanea has not been transferred to Elimatia here.
Harding (1990, p. 37–39) introduced the concept of “true” and “false” apical horns in his treatment of four species of Trichodinium, T. calvus Harding 1990, T. ciliatum (Gocht 1959) Eisenack and Klement 1964, T. discus Harding 1990 and T. speetonense Davey 1974. Although Harding didn’t define “true” and “false”, the first appears to be similar to that displayed by several species of Cribroperidinium and Apteodinium whereas “false” horns are formed by apical tufts of particularly long spinules, which can be fused to varying degrees.
Trichodinium calvus appears to be the only species of this type with a “true” horn and is possibly a taxonomic junior synonym of Apteodinium? albertii Lentin and Williams 1981. In his description of A.? albertii (as Pareodinia spinosa), Alberti (1961, p. 24) refers to a pointed apical horn and very small surface spines 1.5 to 2 μm long, and his illustration (op. cit. Plate 4, Figure 16) suggests some reduction of this ornament on the epicyst; Alberti’s material was of a late Barremian age. All of these features closely match Harding’s (1990, p. 37) observations on T. calvus, also from the late Barremian.
In the present study, Trichodinium ciliatum, T. discus and T. speetonense are all readily transferred to Elimatia. Trichodinium calvus is also transferred to that genus, as Elimatia albertii (Lentin and Williams 1981) n. comb., although recognising that its “true” apical horn is atypical (see Plate 12, Figures 5, 7).
Duxbury (1980, p. 122, 123) described the “Trichodinium-type” body ornament of Cribroperidinium comptum (Duxbury) Stover and Evitt 1978, and this has been confirmed in the current study, together with the possession in some specimens of a tapering, “true” apical horn, very similar to that of Elimatia albertii (compare Plate 12, Figures 1, 5, 7). The LAD of C. comptum was at 27.05 m in Heslerton No. 2 and its range overlaps the late Barremian inception of E. albertii, allowing a possible linking of the two species.