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Carnarvonodinium isfjordica
From Fensome et al., 2019:
Carnarvonodinium isfjordica (Århus, 1992, p.310, figs.4A–I) Duxbury, 2018, p.179. Emendation: Duxbury, 2018, p.179, as
Carnarvonodinium isfjordica. Holotype: Århus, 1992, fig.4E. Originally Boreocysta, subsequently (and now)
Carnarvonodinium. Age: Valanginian.
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Original description: [Arhus, 1992, p. 310]:
Description:
Elongated ellipsoidal Gx-cyst. Body length about twice the body width. The latter varies between 55 and 65 µm. Wall smooth to scabrate, layers not distinguishable (autophragm), but form a complex and variable pattern of partly branching, delicate, approximately 5 µm, occasionally up to 12 µm long, solid processes. Some of these widen distally, where they are at least partly connected by trabeculae that apparently do not reflect paratabulation. Complete ectophragm not preserved.
Apical archeopyle, type (tA) with a deep sulcal notch. The cyst has a tendency to split on both sides of the anterior sulcal paraplate.
Paraplates 1"-6" can also be distinguished due to parasutural splits along the archeopyle margin. 6" is about 9 µm broad.
Emended Diagnosis Duxbury, 2018: A large, thin-walled, elongate ellipsoidal dinoflagellate cyst, with a rounded antapex; a slight antapical
protrusion may occur. Hair-like spines are distributed over the surface of the cyst and these may be free or joined in various ways along their length or distally. The number and arrangement of the spines is variable, but some lineation appears to be present, possibly marking penitabular areas. The antapical pole is granular, and often separated from the rest of the hypocyst by a zone largely devoid of ornament. The archeopyle is apical and deep sutural splits indicate six precingular plates.
Dimensions: Operculum detached: Width – 86 (66) 53 µm. Length – 139 (125) 104 µm. Specimens Measured: 15.
Remarks: This very distinctive species has been transferred to the genus Carnarvonodinium Parker 1988 as it has no clear ectophragm, a feature noted by Århus (1992, p. 310) in his original description. Its diagnosis has been emended to include reference to the granular antapical pole and the characteristic ornament-free zone separating it from the rest of the hypocyst. The last feature is clearly visible in Århus 1992, Figures 4B and 4E.
Carnarvonodinium isfjordicum differs from other species of this genus in its large size and its hair-like ornament. The thin-walled nature of this species often causes folding or breakage of the cyst. An apical archeopyle is clearly demonstrated by precingular sutural splits, but no opercula were recorded here, so that the apical projection typical of this genus (Parker 1988) could not be confirmed. This species is sometimes rare, but can be common (as in the type material from Spitsbergen and off- shore Nordland, Norway), and is a distinctive and valuable marker taxon.
In the present study, this very distinctive, short-ranging species is restricted to the lower Hauterivian, Subzone LKP10.3. This contrasts with Århus (1992, p. 310), who described this species (as Boreocysta isfjordica) from the lower Valanginian, “probably… in the Michalskii ammonite Zone” and from Bjaerke (1978, Table 2) where it was again placed (as Tenua sp. A) within the Valanginian. The Polyptychites michalskii Zone is
equivalent to the Polyptychites Beds of Speeton (Figure 3), significantly older than the occurrence of C. isfjordicum in the present study. This discrepancy in ages might reflect latitudinal range variations, but could be due to differences in macrofossil age-dating of the sections analysed.
Carnarvonodinium isfjordica (Århus, 1992, p.310, figs.4A–I) Duxbury, 2018, p.179. Emendation: Duxbury, 2018, p.179, as
Carnarvonodinium isfjordica. Holotype: Århus, 1992, fig.4E. Originally Boreocysta, subsequently (and now)
Carnarvonodinium. Age: Valanginian.
---------------------------------------------------------------------------------------------------
Original description: [Arhus, 1992, p. 310]:
Description:
Elongated ellipsoidal Gx-cyst. Body length about twice the body width. The latter varies between 55 and 65 µm. Wall smooth to scabrate, layers not distinguishable (autophragm), but form a complex and variable pattern of partly branching, delicate, approximately 5 µm, occasionally up to 12 µm long, solid processes. Some of these widen distally, where they are at least partly connected by trabeculae that apparently do not reflect paratabulation. Complete ectophragm not preserved.
Apical archeopyle, type (tA) with a deep sulcal notch. The cyst has a tendency to split on both sides of the anterior sulcal paraplate.
Paraplates 1"-6" can also be distinguished due to parasutural splits along the archeopyle margin. 6" is about 9 µm broad.
Emended Diagnosis Duxbury, 2018: A large, thin-walled, elongate ellipsoidal dinoflagellate cyst, with a rounded antapex; a slight antapical
protrusion may occur. Hair-like spines are distributed over the surface of the cyst and these may be free or joined in various ways along their length or distally. The number and arrangement of the spines is variable, but some lineation appears to be present, possibly marking penitabular areas. The antapical pole is granular, and often separated from the rest of the hypocyst by a zone largely devoid of ornament. The archeopyle is apical and deep sutural splits indicate six precingular plates.
Dimensions: Operculum detached: Width – 86 (66) 53 µm. Length – 139 (125) 104 µm. Specimens Measured: 15.
Remarks: This very distinctive species has been transferred to the genus Carnarvonodinium Parker 1988 as it has no clear ectophragm, a feature noted by Århus (1992, p. 310) in his original description. Its diagnosis has been emended to include reference to the granular antapical pole and the characteristic ornament-free zone separating it from the rest of the hypocyst. The last feature is clearly visible in Århus 1992, Figures 4B and 4E.
Carnarvonodinium isfjordicum differs from other species of this genus in its large size and its hair-like ornament. The thin-walled nature of this species often causes folding or breakage of the cyst. An apical archeopyle is clearly demonstrated by precingular sutural splits, but no opercula were recorded here, so that the apical projection typical of this genus (Parker 1988) could not be confirmed. This species is sometimes rare, but can be common (as in the type material from Spitsbergen and off- shore Nordland, Norway), and is a distinctive and valuable marker taxon.
In the present study, this very distinctive, short-ranging species is restricted to the lower Hauterivian, Subzone LKP10.3. This contrasts with Århus (1992, p. 310), who described this species (as Boreocysta isfjordica) from the lower Valanginian, “probably… in the Michalskii ammonite Zone” and from Bjaerke (1978, Table 2) where it was again placed (as Tenua sp. A) within the Valanginian. The Polyptychites michalskii Zone is
equivalent to the Polyptychites Beds of Speeton (Figure 3), significantly older than the occurrence of C. isfjordicum in the present study. This discrepancy in ages might reflect latitudinal range variations, but could be due to differences in macrofossil age-dating of the sections analysed.