Excentrodiscus grigorei, Dumitrica, 2019

Dumitrica, Paulian, 2019, Cenozoic Spumellarian Radiolaria With Eccentric Microsphere, Acta Palaeontologica Romaniae 15 (1), pp. 39-60 : 54

Excentrodiscus grigorei nov. sp.

Figures 10 a-d

?1978 Excentrodiscus sp. – Dumitrică, pl. 4, figs. 5-6.

2001 Excentrodiscus sp. – Dumitrică in De Wever et al., p. 124, Fig. 69.2, 69.5.

2010 Excentrodiscus japonicus (Nakaseko & Nishimura) . – Kamikuri, pl. 2, figs. 13a-b, 14a-b.

Description. Cortical test spherical to slightly ovoid, thick-walled in mature stage. Pores circular or oval on the inner side of cortical shell polygonally (pentagonally or hexagonally) framed externally, with sharp crests and thin spines at vertices. Medullary shell double, with a very small eccentric and polyhedral microsphere and a slightly oval outer medullary shell. Outer medullary shell interconnected with microsphere through about 7-8 unequal beams and with the cortical shell by about double number of equal radial bars. All beams cylindrical and not continued among shells.

Material. Numerous specimens in the Middle Miocene (late Badenian) Radiolarian Shale Formation from Subcarpathians and Getic Depression of Romania.

Holotype. Figure 10a, coll. MGL 103564 .

Dimensions. Diameter of microsphere 23 μm, of external medullary shell 70 μm, of cortical shell 150-190 μm.

Etymology. The species is dedicated to the geologist Grigore Popescu who defined for the first time the Radiolarian Shale Formation in the Miocene of Subcarpathian area.

Remarks. This species differs from the specimen illustrated as Excentrodiscus sp. in Dumitrică 1978 (pl. 4, figs. 5- 6) in having a smaller number of pores and thicker cortical shell in mature stage, but resembles the one illustrated in De Wever et al (2001) although both are from the same formation. Specimens assignable to this new species have been illustrated by Kamikuri (2010) from late Neogene of middle to high latitude of North Pacific and assigned to Excentrodiscus japonicus ( Nakaseko & Nishimura, 1974) . However, Nakaseko and Nishimura’s species, originally determined as Prunulum japonicum , differs from Excentrodiscus grigor ei nov. sp. by having many more and much smaller pores. So, the two species are not synonym.

Range and occurrence. Middle Miocene (late Badenian), Radiolarian Shale Formation, Subcarpathians and Getic Depression, Romania.