Sphaerolarnacillium cochleatum, 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 : 47-49

Sphaerolarnacillium cochleatum n. sp.

Figure 27

zoobank.org/ 223A8085-9F66-4938-8C22-37978D99A62B

1978 Trizonium sp. McMillen and Casey, pl. 3, fig. 1.

1987 Tholospira cervicornis Haeckel group; Dworetzky and Morley, pl. 2, fig. 3.

1991 Tholospira cervicornis Haeckel group; Takahashi, p. 91, figs. 7-9 (only).

1995 Pylonidae gen. et sp. indet. van de Paverd, pl. 58, fig. 7.

1995 Phorticium ? sp. van de Paverd, pl. 59, figs. 1, 7.

Etymology. Latin adjective "cochleatus" (-a, -um),

meaning spiral/screw formed.

Holotype. Specimen in Figure 27.12-14 from the sample YDY05-01.

Paratype. Specimen in Figure 27.9-10 from the sample YDY05-01.

Description. Test shows a highly spiraled spherical to oval shape with numerous short radial spines and consists of a larnacillid central combination, two pseudo-concentric shells with spiral girdles, and incompletely developed girdles. Cylindrical radial spines are radially distributed during any ontogenetic stage of the test except in specimens with only the larnacillid central combination. Well-regulated girdles are coiled along either the Lt-, Sg-, or Pl-axis. The 1st pseudo-concentric shell consists of S2a-, S2b-, and S2c-girdles and appears triangular. This triangular shadow is formed by a combination of the other side of the twin S2b-girdle and both sides of the twin S2a-girdles. In addition, one side of the twin S2a-girdle is generally fragile and coarsely framed. The S2c-girdle develops vertically to the orientation of the S2b-girdles and they turned irregularly to form a spherical appearance. The S2c-girdles and subsequent girdles join at similar diameter levels of the test to form the 1st pseudo-concentric shell. The pseudo-concentric shell has gates or openings related to the spiral girdles. The 1st pseudo-concentric shell includes G2 gates and G3 gates. There “para-gates” are present in the outmost cap-like twin girdles. Fine, cylindrical radial spines emerge from the larnacillid central combination, which consists of the larnacillid central combination. The 2nd pseudo-concentric shell is composed of spiral girdles. Radial spines that arise from the larnacillid central combination become pillar beams beneath the 2nd pseudo-concentric shell because these radial spines do not pierce through the 2nd pseudo-concentric shell. Instead, new pillar beams arise from the 1st pseudo-concentric shell and extend outward from the 2nd pseudo-concentric shell to form cylindrical radial spines. Because the 1st pseudo-concentric shell is composed of spiral girdles, several para-gates are present, and these spiral girdles have an overall irregular appearance. Pores on the larnacillid central combination are sub-circular and small. Those on the 1st pseudo-concentric shell arelarger than those on the inner shell, and smaller than those on the outer shell. Those on the 2nd pseudo-concentric shell are large and polygonal with very thin pore frames.

Remarks. Sphaerolarnacillium cochleatum is distinguished from Sphaerolarnacillium exactum n. sp. in that the latter has more regular pseudo-concentric shells and an overall flattened appearance. Furthermore, Sphaerolarnacillium cochleatum has gates in its pseudo-concentric shells, but there are no gates in the pseudo-concentric shells of Sphaerolarnacillium exactum . Sphaerolarnacillium cochleatum can be differentiated from Sphaerolarnacillium tanzhiyuani n. sp. based on the former’s larger size and more elliptical shape.

Dimensions. Based on the holotype specimen. The height of the 1st pseudo-concentric shell: ca. 93–98 μm; The length and width of the 2nd pseudo-concentric shell: 166.5 μm and 133.7 μm. The ratio of length to width of the 2nd pseudo-concentric shell: ca. 1.2.

Figures

FIGURE 27. Photographs of the encountered morphotypes of Sphaerolarnacillium cochleatum gen. et n. sp. All are Fr-view at Type 2. Scale bar equals 0.1 mm. All specimens are from YDY05-01.