Circodiscus biorbiculus, Zhang & Suzuki, 2017

Zhang, Lanlan & Suzuki, Noritoshi, 2017, Taxonomy and species diversity of Holocene pylonioid radiolarians from surface sediments of the northeastern Indian Ocean, Palaeontologia Electronica (Cambridge, England: 2003) 7 (8), pp. 1-68 : 55-56

Circodiscus biorbiculus n. sp.

Figure 31.3-4

zoobank.org/ 478A4DEB-55EB-4D5F-98DF-31AEEE9AB626

aff. 1987 Lithocyclia heteropora Haeckel ; Boltovskoy, pl. 1, fig. 12.

1991 Circodiscus spp. Group Takahashi, pl. 20, figs. 8-9 (only).

Etymology. The Latin prefix “bi” and male noun “orbiculus”, meaning two disks. Grammatical male noun.

Holotype. Specimen in Figure 31.3-4 from the sample YDY05-01.

Description. Test consists of a larnacillid central combination, a rounded quadrangular 1st ring, a subcircular 2nd ring, and a peripheral velum. Based on the orientation of the central combination, the flat disk surface is parallel to the Sg-plane in Type 1 coordinates. The Lt-axis in Type 1 coordinates is parallel to the Ug-axis in Type 2 coordinates, and the Pl-axis is parallel to the Pr-axis. The 2nd ring is lattice, and shows a flat, convex lens shape. The peripheral velum is latticed and connected with the 2nd ring by sharp constriction. The outline of the peripheral velum is irregular.

Remarks. Circodiscus biorbiculus n. sp. is only distinguishable from Circodiscus microporus based on the lack of a 3rd (or more) ring. Instead of a ring, a peripheral velum is developed in C. birobiculus n. sp. that is wider than the width of the 3rd chamber (ring) of Circodiscus microporus , and consequently, there is no possibility of uncovering different ontogenetic stages of this single species. A chamber is a circular zone boredered by rings.

Dimensions. Based on the holotype specimen. Diameters of outermost shell along the Pl- and Lt-axes: 9.6 μm and 9.0 μm (the central combination), 22.6 μm and 36.2 μm (1st ring), 74 μm and 85 μm (2nd ring), and 147 μm and 166.4 μm (the peripheral velum). The length ratio of the Lt-axis to the Pl-axis: 0.94 (the central combination), 1.6 (1st ring), 1.1 (2nd ring), and 1.1 (the peripheral velum).

Figures

FIGURE 31. Photographs of the encountered morphotypes of Circodiscus. 1-2, Circodiscus amphitrites (Ehrenberg, 1854b); 3-4, Circodiscus biorbiculus n. sp.; 5-14, Circodiscus microporus (Stöhr, 1880); and 15-16, Circodiscus pseudomicroporus n. sp. All are Sg-view at Type1, Fr-view at Type 2. Scale bar equals 0.1 mm. All specimens are from YDY05-01.