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Dinogymnium aerlicum
From Fensome et al., 2019:
Dinogymnium aerlicum Londeix et al., 1996, p.380, pl.1, figs.10a–c,11a–c; text-figs.7E–F. Holotype: Londeix et al., 1996, pl.1,
figs.11a–c; text-fig.7E. Age: late Berriasian.
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Diagnosis: Proximate acavate asymmetrical test with a biconical shape. The single-layered wall is thick and its surface is smooth to scabrate. Trichocyst pores are absent. The conical epitest has a rounded apex and is similar in size to the more rounded hypotest which exhibits a distinctly pointed antapex. Ornamentation is more developed on the epitest which bears a few strongly to faintly marked ridges. Ridges are faintly expressed or absent on the hypotest. Additional heterocostate ridges are absent. The cingulum is well depressed and relatively wide. The "archeopyle" is apical, recognizable as a triangular to circular opening on the apex. The operculum is either attached ormissing.
Dimensions: Holotype: Test length = 38 µm; epitestal length = 18 µm; hypotestal length = 14 µm; test breadth = 23 µm; cingulum height = 2 µm; cingulum index = 0.50.
Paratype: Test length = 43 µm; epitestal length = 23 µm; hypotestal length = 19 µm; test breadth = 25 µm; cingulum height = 3 µm; cingulum index = 0.53.
Overall size range: Test length = 35 (38) 43 µm; epitestal length = 18 (19) 23 µm; hypotestal length = 13 (15) 19 µm; test breadth = 22 (23.5) 25 µm; cingulum height = 3 (3) 3 µm; cingulum index = 0.50 (0.52) 0.54; number of measured specimens = 3.
Remarks: Although very few specimens of this species have been found, its morphological features are regarded as sufficiently characteristic for the erection of a new species. One of the specimens exhibits an antapical bulge instead of a distinctively pointed antapex and bears very faintly expressed ridges compared to the other two. This probably reflects the intra-specific variability typical of the genus or possibly variations in quality of preservation. Dinogymnium aerlicum Londeix, Pourtoy and Fenton, sp. nov. represents the earliest known record of the genus Dinogymnium.
Comparisons: Its asymmetrical biconical shape and distinctively pointed antapex, in addition to its very small size distinguishes D. aerlicum Londeix, Pourtoy and Fenton, sp. nov. from the other Lower Cretaceous species of Dinogymnium although it is otherwise very close to D. cf. acuminatum.
Dinogymnium biconicum Jain and Millepied, 1975 has a slightly pointed apex and antapex, but its size range is between 5 and 8 times greater than that of D. aerlicum Londeix, Pourtoy and Fenton, sp. nov.
Dinogymnium aerlicum Londeix et al., 1996, p.380, pl.1, figs.10a–c,11a–c; text-figs.7E–F. Holotype: Londeix et al., 1996, pl.1,
figs.11a–c; text-fig.7E. Age: late Berriasian.
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Diagnosis: Proximate acavate asymmetrical test with a biconical shape. The single-layered wall is thick and its surface is smooth to scabrate. Trichocyst pores are absent. The conical epitest has a rounded apex and is similar in size to the more rounded hypotest which exhibits a distinctly pointed antapex. Ornamentation is more developed on the epitest which bears a few strongly to faintly marked ridges. Ridges are faintly expressed or absent on the hypotest. Additional heterocostate ridges are absent. The cingulum is well depressed and relatively wide. The "archeopyle" is apical, recognizable as a triangular to circular opening on the apex. The operculum is either attached ormissing.
Dimensions: Holotype: Test length = 38 µm; epitestal length = 18 µm; hypotestal length = 14 µm; test breadth = 23 µm; cingulum height = 2 µm; cingulum index = 0.50.
Paratype: Test length = 43 µm; epitestal length = 23 µm; hypotestal length = 19 µm; test breadth = 25 µm; cingulum height = 3 µm; cingulum index = 0.53.
Overall size range: Test length = 35 (38) 43 µm; epitestal length = 18 (19) 23 µm; hypotestal length = 13 (15) 19 µm; test breadth = 22 (23.5) 25 µm; cingulum height = 3 (3) 3 µm; cingulum index = 0.50 (0.52) 0.54; number of measured specimens = 3.
Remarks: Although very few specimens of this species have been found, its morphological features are regarded as sufficiently characteristic for the erection of a new species. One of the specimens exhibits an antapical bulge instead of a distinctively pointed antapex and bears very faintly expressed ridges compared to the other two. This probably reflects the intra-specific variability typical of the genus or possibly variations in quality of preservation. Dinogymnium aerlicum Londeix, Pourtoy and Fenton, sp. nov. represents the earliest known record of the genus Dinogymnium.
Comparisons: Its asymmetrical biconical shape and distinctively pointed antapex, in addition to its very small size distinguishes D. aerlicum Londeix, Pourtoy and Fenton, sp. nov. from the other Lower Cretaceous species of Dinogymnium although it is otherwise very close to D. cf. acuminatum.
Dinogymnium biconicum Jain and Millepied, 1975 has a slightly pointed apex and antapex, but its size range is between 5 and 8 times greater than that of D. aerlicum Londeix, Pourtoy and Fenton, sp. nov.