Heterosestrum formosum bispinum ( Tochilina, 1972 )

Popova, Irina M., Baumgartner, Peter O., Guex, Jean, Tochilina, Svetlana V. & Glezer, Zoya I., 2002, Radiolarian biostratigraphy of Paleogene deposits of the Russian Platform (Voronesh Anticline), Geodiversitas 24 (1), pp. 7-59 : 35

Heterosestrum formosum bispinum ( Tochilina, 1972) emend. ( Fig. 11F )

Amphicyclia bispina Tochilina, 1972: 134 , pl. 1.

Heterosestrum formosum – Kozlova 1999: pl. 34, fig. 1.

Heterosestrum sp. cf. formosum – Kozlova 1999: pl. 28, fig. 9.

Heterosestrum sp. aff. tschujenkoi – Kozlova 1999: pl. 41, fig. 2.

GEOGRAPHIC DISTRIBUTION. — Voronesh Anticline.

STRATIGRAPHIC RANGE. — Middle Eocene, Kievsky Group, Fedorovskaya Formation, Voronesh Anticline, Pirogovo Village, well 510C, 44.0 m depth.

REMARKS

The quantity of outershell spines and peripheral concentric inner shells (the double medullar shell’s central part has a stable construction) are very changeable characteristics for Heterosestrum formosum . However, in the same sample it was observed abundant amount of specimens bearing only two (or only three to six) polar spines and three to five concentric inner shells. This phenomena can be explained by local environmental conditions of the siliceous microfauna existence. Because of that the latter gave the rise for a different morphotype better adjusted for special life conditions. In order to reflect this local (but very important for age determination) phenomena and to preserve the stratigraphical resolution of this group, we decided not to generalize its systematics, joining under the name Heterosestrum formosum all its possible morphotypes, but to introduce a group of subspecies, where the name of each morphotype was earlier ( Tochilina 1972) described as a different species, because of a difference in quantity of the inner shells and outershell spines. The attribution of Amphicyclia trispina , A. quadrispina and A. pentaspina to H. shabalkini ( Lipman, 1949) by Kozlova (1999) is not correct, as the most characteristic feature of latter – the amplification of the thickness of the shell in its peripheral part (lateral view) – was not observed ( Fig. 10D, G ), or illusive, when the central part of an outershell is broken ( Fig. 12O ).

Figures

FIG. 11. — Middle-early late Eocene Radiolarian association, Pirogovo Village, Well 510C, 44.0 m; A, B, Anthocyrtidium pupa Clark & Campbell, 1942; C, Lophocyrtis aspera (Ehrenberg, 1873); D, Clathrospyris sandellae Goll, 1980; E, Callimitra clavipes (Clark & Campbell, 1945); F, Heterosestrum formosum bispinum (Tochilina, 1972) emend.; G, Theocorys anaclasta Riedel & Sanfilippo, 1970; H, Axoprunum visendum (Kozlova, 1966); I, Lophocyrtis ex. gr. Calocyclas semipolita Clark & Campbell, 1942; J, K, Hexacontium sp.; L, Lychnocanium sp. B; M Lophocyrtis norvegiensis (Bjørklund & Kellogg, 1972); N, Lophocyrtis auriculaleporis (Clark & Campbell, 1942); O, Lychnocanium sp. A; P, Desmospyris ex. gr. anthocyrtoides Bütschli, 1882. Scale bar: 100 µm.

FIG. 10. — Early Eocene Radiolarian association, Petropavlovka Village, Well 730, interval 44.3 m; A, B, Periphaena perplexus (Clark & Campbell, 1942); C, F, J, Haliomma (?) faceta (Krasheninnikov, 1960); D, G, Heterosestrum formosum (Tochilina, 1970); E, Periphaena sp. aff. Heliodiscus inca (Clark & Campbell, 1942); H, K, Stylotrochus festivus Clark & Campbell, 1942; I, Heterosestrum (?) sp.; L, M, Amphicraspedium praemurrayanum Kozlova, 1999; N, Ommatogramma biconstrictus (Lipman, 1953). Scale bars: 100 µm.

FIG. 12. — Middle Eocene Radiolarian association, Pirogovo Village, Well 510C, interval 44.0 m (except 8: 730C, 44.3 m); A, Ceratocyrtis charlestonensis (Clark & Campbell, 1945); B, E, F, Ceratocyrtis sp. aff. stigi (Bjørklünd, 1976); C, Lithomelissa spongiosa Bütschli, 1882; D, N, Giraffospyris didiceros (Ehrenberg, 1875); G, Patagospyris morkleyensis (Clark & Campbell, 1942); H, K, Giraffospyris sp. aff. didiceros (Ehrenberg, 1875); I, J, Petalospyris tumidula Kozlova, 1966; L, M, Peripyramis magnifica (Clark & Campbell, 1942) sensu Kozlova 1999; O, Heterosestrum formosum (Tochilina, 1970), saggittal view. Scale bars: 50 µm.