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Nelchinopsis crinita
Locus typicus: Fetchham Mill, England
Stratum typicum: Cenomanian
Original diagnosis: Davey, 1969, p. 137
Shell subspherical, periphragm granular and giving rise to numerous, finc, flexuous spines. Sutural crests low, bearing numerous spines. Cingulum wide, composed of elongate plates. Epitract smaller than hypotract. Archaeopyle not normally visible.
Dimensions: shell diameter 24 (30.1) 38 µm, length of spines 6-19 µm.
Original description: Davey, 1969, p. 137
The periphragm granules, which are evenly spaced on the shell surface, are up to 0.5 µm high, and often form the bases of the hair-like spines. The latter tend to be especially concentrated along the sutures, and because of this tendency and the spherical form of the shell, it has not been possible to fully formulate a tabulation. However, precingular, cingular and postcingular plates are quite obvious when the orientation is favourable, the precingular plates being smaller than the postcingular plates. The cingulum is broad, c. 5 µm. The archaeopyle, although it has not been observed, is probably apical.
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Remarks Duxbury 2023:
Remarks: In his re-assessment of Nelchinopsis kostromiensis and Gardodinium trabeculosum, Harding (1996, p. 351) stated that, “These two taxa are the only fossil dinocysts so far described which show parasutural features developed on ectophragmal wall layers”. However, well-preserved specimens of Microdinium? crinitum, transferred here to Nelchinopsis Wiggins 1972 emend. Harding 1996 also show these features. In his description of Nelchinopsis crinita (as Microdinium? crinitum), Davey (1969, p. 137) noted “periphragm granules”, often forming the bases of hair-like spines, “concentrated along the sutures”. He also noted that, “precingular, cingular and postcingular plates are quite obvious when the orientation is favourable”. It is difficult, because of the common distortion of specimens and the long, flexuous nature of the spines, to fully assess the morphology of this species, but in the current study the following characteristics were noted:
• a delicate, spheroidal endocyst with a low, distally rounded apical prominence
• a dense cover of numerous, very slender and relatively short spines
• a delicate, smooth to very finely microperforate ectophragm supported by the short spines
• sutural ridges or low crests marking a tabulation of variable clarity and bearing relatively widely-spaced, long, flexuous spines
• an apical archeopyle
These features support the transfer of this species to Nelchinopsis.
Nelchinopsis crinita n. comb. is a long-ranging species, originally described throughout the Cenomanian in Davey (1969), confirming the range (as Cometodinium obscurum) quoted by Clarke and Verdier (1967, text-figs. 32, 33). Clarke and Verdier also recorded this species in the early Turonian. In the current study, N. crinita was consistently present between Speeton Bed C4C (late Hauterivian, gottschei Zone) and the top of the studied section. Because of the wide sampling gap between Beds C6 and C4C, the FAD is assumed to be lower, but still within the late Hauterivian.
Stratum typicum: Cenomanian
Original diagnosis: Davey, 1969, p. 137
Shell subspherical, periphragm granular and giving rise to numerous, finc, flexuous spines. Sutural crests low, bearing numerous spines. Cingulum wide, composed of elongate plates. Epitract smaller than hypotract. Archaeopyle not normally visible.
Dimensions: shell diameter 24 (30.1) 38 µm, length of spines 6-19 µm.
Original description: Davey, 1969, p. 137
The periphragm granules, which are evenly spaced on the shell surface, are up to 0.5 µm high, and often form the bases of the hair-like spines. The latter tend to be especially concentrated along the sutures, and because of this tendency and the spherical form of the shell, it has not been possible to fully formulate a tabulation. However, precingular, cingular and postcingular plates are quite obvious when the orientation is favourable, the precingular plates being smaller than the postcingular plates. The cingulum is broad, c. 5 µm. The archaeopyle, although it has not been observed, is probably apical.
-----------------------------------------------------------------------------------------------------------------
Remarks Duxbury 2023:
Remarks: In his re-assessment of Nelchinopsis kostromiensis and Gardodinium trabeculosum, Harding (1996, p. 351) stated that, “These two taxa are the only fossil dinocysts so far described which show parasutural features developed on ectophragmal wall layers”. However, well-preserved specimens of Microdinium? crinitum, transferred here to Nelchinopsis Wiggins 1972 emend. Harding 1996 also show these features. In his description of Nelchinopsis crinita (as Microdinium? crinitum), Davey (1969, p. 137) noted “periphragm granules”, often forming the bases of hair-like spines, “concentrated along the sutures”. He also noted that, “precingular, cingular and postcingular plates are quite obvious when the orientation is favourable”. It is difficult, because of the common distortion of specimens and the long, flexuous nature of the spines, to fully assess the morphology of this species, but in the current study the following characteristics were noted:
• a delicate, spheroidal endocyst with a low, distally rounded apical prominence
• a dense cover of numerous, very slender and relatively short spines
• a delicate, smooth to very finely microperforate ectophragm supported by the short spines
• sutural ridges or low crests marking a tabulation of variable clarity and bearing relatively widely-spaced, long, flexuous spines
• an apical archeopyle
These features support the transfer of this species to Nelchinopsis.
Nelchinopsis crinita n. comb. is a long-ranging species, originally described throughout the Cenomanian in Davey (1969), confirming the range (as Cometodinium obscurum) quoted by Clarke and Verdier (1967, text-figs. 32, 33). Clarke and Verdier also recorded this species in the early Turonian. In the current study, N. crinita was consistently present between Speeton Bed C4C (late Hauterivian, gottschei Zone) and the top of the studied section. Because of the wide sampling gap between Beds C6 and C4C, the FAD is assumed to be lower, but still within the late Hauterivian.