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Wilsonidium michouxi
Plate 12, figs. 11, 12, 16, 20
Wilsonidium sp. 2: Michoux, 1988, p. 40, Pl. 11, figs. 5, 6, 9.
Etymology. In honor of palynologist Daniel Michoux.
Holotype. IGG, no. 9/23-02; Russia, Lower Volga region, Ravninnaya R-43 borehole, interval of 135.0–128.1 m, sample R-43/56; Middle Eocene.
Description. Peridinioid circumcavate cysts are of rhomboidal shape. The right antapical horn is significantly shortened. The lateral sides of the pericyst are straight, with a serrated edge. The endocyst is oval in shape. The periphragm and endophragm are dense and granular. The pericoel is wide. Tabulation is marked by low, sparse spinules and tubercles on the periphragm, oriented along the sutural lines; on the lateral parts of the cyst, there are rows of shortened, rudimentary processes. The cingulum is marked by rows of spinules and grains, sometimes bordered by thin folds. The contours of the sulcus are bounded by spinules. The archaeopyle is rectangular in shape, with rounded corners, intercalary (2a). The operculum is usually free.
Dimensions. Holotype (Pl. 12, fig. 11): total length 122.5 μm, total width 90 μm, central body length 80 μm, central body width 65 μm. Paratype (Pl. 12, fig. 12): total length 114 μm, total width 92 μm, central body length 76 μm, central body width 68 μm. Other specimens: total length 94–126 μm, total width 76–100 μm, central body length 68–86 μm, central body width 61–75 μm. Eight specimens were measured.
Comparison. Wilsonidium michouxi sp. nov. is comparable to Wilsonidium tabulatum (Wilson, 1967) in the pattern of periphragm ornamentation (short processes); however, it differs in the shortened horns, a wider pericoel, and a punctuate periphragm ornamentation. The species resembles Wilsonidium intermedium (Cookson et Eisenack, 1961) in the shape of the cyst and width of the pericoel; however, the latter has a more defined pericyst ornamentation in the form of thin folds. The species Wilsonidium michouxi sp. nov. resembles Wilsonidium compactum Michoux, 1988 in the shape of the cyst; however, the pericyst of the new species is usually clearly rhomboidal in shape, with a wide pericoel, and ornamented with spinules rather than processes. The morphology of the new species is most similar to that of Wilsonidium sp. 2 Michoux, 1988 in the rhomboidal shape of the cyst, wide pericoel, and punctuate sutural ornamentation of the periphragm (Michoux, 1988, Pl. 11, figs. 5, 6, 9), which served as the basis for the name of the new species.
Remarks. Cysts of Wilsonidium michouxi sp. nov. are strongly flattened in the dorsoventral direction; therefore, the sutural ornamentation is usually fused on the dorsal and ventral (Fig. 3b) surfaces of the pericyst and hardly distinguishable.
Material. Eight specimens from the type locality.
Wilsonidium sp. 2: Michoux, 1988, p. 40, Pl. 11, figs. 5, 6, 9.
Etymology. In honor of palynologist Daniel Michoux.
Holotype. IGG, no. 9/23-02; Russia, Lower Volga region, Ravninnaya R-43 borehole, interval of 135.0–128.1 m, sample R-43/56; Middle Eocene.
Description. Peridinioid circumcavate cysts are of rhomboidal shape. The right antapical horn is significantly shortened. The lateral sides of the pericyst are straight, with a serrated edge. The endocyst is oval in shape. The periphragm and endophragm are dense and granular. The pericoel is wide. Tabulation is marked by low, sparse spinules and tubercles on the periphragm, oriented along the sutural lines; on the lateral parts of the cyst, there are rows of shortened, rudimentary processes. The cingulum is marked by rows of spinules and grains, sometimes bordered by thin folds. The contours of the sulcus are bounded by spinules. The archaeopyle is rectangular in shape, with rounded corners, intercalary (2a). The operculum is usually free.
Dimensions. Holotype (Pl. 12, fig. 11): total length 122.5 μm, total width 90 μm, central body length 80 μm, central body width 65 μm. Paratype (Pl. 12, fig. 12): total length 114 μm, total width 92 μm, central body length 76 μm, central body width 68 μm. Other specimens: total length 94–126 μm, total width 76–100 μm, central body length 68–86 μm, central body width 61–75 μm. Eight specimens were measured.
Comparison. Wilsonidium michouxi sp. nov. is comparable to Wilsonidium tabulatum (Wilson, 1967) in the pattern of periphragm ornamentation (short processes); however, it differs in the shortened horns, a wider pericoel, and a punctuate periphragm ornamentation. The species resembles Wilsonidium intermedium (Cookson et Eisenack, 1961) in the shape of the cyst and width of the pericoel; however, the latter has a more defined pericyst ornamentation in the form of thin folds. The species Wilsonidium michouxi sp. nov. resembles Wilsonidium compactum Michoux, 1988 in the shape of the cyst; however, the pericyst of the new species is usually clearly rhomboidal in shape, with a wide pericoel, and ornamented with spinules rather than processes. The morphology of the new species is most similar to that of Wilsonidium sp. 2 Michoux, 1988 in the rhomboidal shape of the cyst, wide pericoel, and punctuate sutural ornamentation of the periphragm (Michoux, 1988, Pl. 11, figs. 5, 6, 9), which served as the basis for the name of the new species.
Remarks. Cysts of Wilsonidium michouxi sp. nov. are strongly flattened in the dorsoventral direction; therefore, the sutural ornamentation is usually fused on the dorsal and ventral (Fig. 3b) surfaces of the pericyst and hardly distinguishable.
Material. Eight specimens from the type locality.