Circodiscus pseudomicroporus, 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 : 57

Circodiscus pseudomicroporus n. sp.

Figure 31.15-16

zoobank.org/ 67E17731-0450-40C7-9CFC-FE6C9E6176F6

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

Etymology. As it is likely to be misidentified as Circodiscus microporous , this new species is named showing similarity to this species. The Latin word “porus” is a grammatical masculine noun, meaning pores.

Holotype. Specimen in Figure 31.15-16 from the sample YDY05-01.

Description. Test consists of a larnacillid central combination, a quadrangular 1st ring, an ellipsoid 2nd ring, and an ellipsoid 3rd ring with a bore pylome. 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 of the 1st ring, and the Pl-axis is parallel to the Pr-axis of the 1st ring. The 2nd chamber looks like a flat, convex lens. Pores on the 2nd chamber are circular to subcircular and as large as 8–9 μm in diameter, with a thin pore frame. The 3rd ring is connected to the 2nd ring by numerous pillar beams throughout the 2nd chamber. The 3rd ring resembles a flat convex lens with numerous small pores (4–5 μm in diameter). A bore pylome on the 3rd ring is surrounded by a thin, porous wall, but there is no distinctive tunnel-like funnel inside the test. The shape of each ring changes from a quadrangular outline (the ratio of the Lt-axis to the Pl-axis = 1.4), to a subcircular outline (the ratio is 1.1), and then to a vertically oblong outline (the ratio is 0.9). Several short radial spines extend from some of the pillar beams on the Sg-plane.

Remarks. Circodiscus pseudomicroprus n. sp. differs from all other Circodiscus species because of its distinctively large pores on the 1st chamber (ring). The number of rings in Circodiscus pseudomicroporus n. sp. is the same as number of rings in Circodiscus microporus ( Stöhr, 1880) , but the former taxon easily distinguished from the latter based on the former’s larger pores on the 1st chamber (ring) and the smaller overall size.

Dimensions. Based on the holotype specimen. The diameters along the Pl- and Lt-axes: 7.8 μm and 8.3 μm (the central combination), 22.1 μm and 30.8 μm (1st ring), 59 μm and 65 μm (2nd ring), and 100 μm and 87 μm (3rd ring). The length ratio of the Lt-axis to the Pl-axis: 1.1 μm (the central combination), 1.4 μm (1st ring), 1.1 (2nd ring), and 0.9 μm (3rd ring). The width of the bore pylome on the 3rd ring: 16.5 μm.

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.