Excentrococcus annulatus Dumitrică, 1978

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

Excentrococcus annulatus Dumitrică, 1978 .

Figures 8a, 8c

1972 Phacodiscidae ? gen. indet. Petrushevskaya & Kozlova, pl. 19, fig. 15.

1973 Xiphospira sp. cf. X. circularis Kling , p. 635, pl. 7, fig. 16, non 11-15, 17.

1978 Excentrococcus annulatus Dumitrică , p. 238, pl. 2, fig. 12; pl. 5, figs. 19, 23.

1992 Excentrococcus annulatus Dumitrică – Sugiyama & Furutani, p. 202, pl. 12, fig. 4;?pl. 16, fig. 4.

1992 Excentrosphaerella sphaeroconcha Dumitrică – Sugiyama & Furutani, p. 202, pl. 12, figs. 1, 2;?pl. 16, fig. 3.

1999 Perichlamidium sp. cf. Ommatodiscus perichlamydium Dreyer – Tan & Chen, p. 209, fig. 5 – 122.

2004 Excentrococcus annulatus Dumitrică. – Kamikuri et al., pl. 8, fig. 10.

Description. Test flat consisting of a double medullary shell with a very small eccentric microsphere; this structure surrounded by two to maximum six latticed circular or oval rings. When number of rings is maximum, shell is oval with an end open and external outermost rings are thinner, irregular and with smaller pores.

Dimensions. Maximum length of shell around 150-160 μm.

Remarks. The species is very variable in shape and number of rings, probably depending on the biological age of specimens and environment. The common number of shells is six and maximum eight, as the specimen illustrated in Fig. 8a of the present paper or in Tan & Chen (1999) and Kamikuri et al. (2004). Up to the level of four shells the rings have large pores. The fifth and sixth rings are less regular and their pores are smaller, and the outermost seems to become slightly spongy. As the species is disc-shaped and the outer medullary shell is partly outside (fig. 8c), the maximum thickness of the disc is as great as the diameter of this shell. As a rule, the largest or the most complete specimens are oval and have a pylome marked by an indentation at one end ( Fig. 8a in the present paper and in Kamikuri et al., 2004) or by an open ring ( Tan & Chen, 1999). This pylome or indentation is situated on the direction in which the microsphere is most close to outer medullary shell. This signifies that there is a correlation between the position of the microsphere and the pylome.

Range and occurrence. Middle Miocene to Recent, cosmopolitan.

Figures

Fig. 8 a, c - Excentrococcus annulatus Dumitrică; a – mature specimen, face view, DSDP 21-205-7-1, 70-72 cm, scale bar 100 μm; c – other specimen, transversal section along the longitudinal axis showing the eccentric microsphere, DSDP 21-206-29CC, scale bar = 100 μm. b, f, g - Heliodiscus riedeli nov. sp., PROA 96P. d, e, h – Heliodiscus bipolaris nov. sp. focused at centre, on surface, and in lateral view, respectively, scale bar = 50 μm, DSDP 21-206-29CC.