Sphaerolarnacillium exactum, 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 : 49-50

Sphaerolarnacillium exactum n. sp.

Figure 28

zoobank.org/ AF5B32CE-D9BD-4C19-99B7-ECA749124FA9

1979 Pylospira octopyle Haeckel ? Nigrini and Moore, p. S139-140, pl. 17, fig. 6c (only).

Etymology. Latin adjective “exactus” (-a, -um), meaning accurate.

Holotype. Specimen in Figure 28.6-8 from the sample YDY05-01.

Paratype. Specimen in Figure 28.3-5 from the sample YDY05-01.

Description. Test is flattened and ellipsoid in shape with several short radial spines and consists of a larnacillid central combination, two complete pseudo-concentric shells, and twin cap-like pseudo-concentric shells. Cylindrical radial spines are radially distributed at any ontogenetic stage of the test. Well-regulated girdles are coiled along either the Lt-, Sg-, or Pl-axis. The complete larnacillid central combination appears flattened and ellipsoid in shape. The 1st and 2nd pseudo-concentric shells have no gates. The Ug-axis of the test in Type 2 coordinates is parallel to the Lt-axis in Type 1 coordinates, whereas the Pr-axis of the test in Type 2 coordinates is oriented parallel to the Pl-axis. The 2nd pseudo-concentric shell also has a flattened ellipsoid shape, but it shows a more circular outline than the larnacillid central combination. The 2nd pseudo-concentric shell is connected with the 1st pseudo-concentric shell by several pillar beams. Some of these pillar beams are derived from the Sg-rods and extend along the boundary between the S2a- and S2b-girdles. In a fully mature specimen, narrow cap-like girdles develop on both sides of the 2nd pseudo-concentric shell along the Lt-axis. No gates are present in these outermost cap-like twin girdles. Pores on the 1st pseudo-concentric shell are sub-circular to rounded polygonal in shape and small in size. Those on the 2nd pseudo-concentric shell are large and polygonal with very thin pore frames.

Remarks. Sphaerolarnacillium exactum n. sp. is easily distinguished from any other Sphaerolarnacillium species based on its more regularly formed pseudo-concentric shells and overall flattened

ZHANG & SUZUKI: TAXONOMY OF HOLOCENE PYLONIOID appearance. Sphaerolarnacillium exactum n. sp. has no gates in the pseudo-concentric shells. However, Sphaerolarnacillium cochleatum and Sphaerolarnacillium tanzhiyuani both have gates or openings related to the spiral girdles.

Dimensions. Based on the holotype specimen. The length and width of the 1st pseudo-concentric shell: 61.3 μm and 45.9 μm; The length and width of the 2nd pseudo-concentric shell: 111.0 μm and 107.2 μm. The height of the cap-like pseudo-concentric shell: 23 μm. The size ratio of the 2nd pseudo-concentric shell to the 1st pseudo-concentric shell: ca. 1.8 in length and ca. 2.3 in width.

Figures

FIGURE 28. Photographs of the encountered morphotypes of Sphaerolarnacillium exactum n. sp. All are Fr-view at Type 2. Scale bar equala 0.1 mm. All specimens are from YDY05-01.