Phorticium itakii, 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 : 45

Phorticium itakii n. sp.

Figure 24.4-6

zoobank.org/ CF919390-DE41-429D-AADB-666B55AAFB07

2008 Phorticium pylonium Haeckel ; Itaki, Minoshima, and Kawahata, pl. 2, figs. 15- 16.

Etymology. Takuya Itaki who illustrated a typical specimen in his paper.

Holotype. Specimen in Figure 24.4-6 from the sample YDY05-01.

Description. The test is sub-rectangular in shape (the length ratio of the Fr-axis to the Pr-axis: ca. 1.3–1.4) in Sg-view, and consists of an elongate central combination, an elliptical 1st pseudo-concentric shell, a 2nd pseudo-concentric shell with two large apertures in one side of the test in the Sg-view, and numerous robust radial spines. The 1st pseudo-concentric shell is completely latticed in its fully mature form. The 2nd pseudo-concentric shell is roughly sub-rectangular in shape with a rough surface. Three to six pillar beams extend from both ends of the 1st pseudo-concentric shell in the Lt-axis direction in Type 1 coordinates, and these beams connect to the 2nd pseudo-concentric shell. Some of these pillar beams pierce through the 2nd pseudo-concentric shell to form robust, cylindrical radial spines. Pores are subcircular and small (4–7 μm in diameter) on the 1st pseudo-concentric shell, and polygonal and moderate in size (10–14 μm in diameter) on the 2nd pseudo-concentric shell. Four or five pores are aligned along the Lt-axis at the joint between the 1st and 2nd pseudo-concentric shells, and eight to 12 pores are aligned along the Pl-axis on the 2nd pseudo-concentric shell. Pore frames of the 1st and 2nd pseudo-concentric shells are thin. The size ratio of the 2nd pseudo-concentric shell to the 1st pseudo-concentric shell is ca. 2.4 along the Lt-axis and 2.8 along the Pl-axis.

Remarks. Phorticium itakii n. sp. is characterized by robust radial spines, three to six pillar beams visible through the gates of the 2nd pseudo-concentric shell, and a sub-rectangular 2nd pseudo-concentric shell with larger pores. Phorticium itakii n. sp. is easily confused with Phorticium pylonium Haeckel, 1887 ; however, P. itakii n. sp. differs from P. pylonium in former’s more robust spines between the central combination and 1st pseudo-concentric shell. Phorticium itakii n. sp. differs from Phorticium clevei ( JØrgensen, 1899) in that the former typically has a quadrangular 2nd pseudo-concentric shell and a larger size ratio between the 2nd pseudo-concentric shell and the 1st pseudo-concentric shell. Phorticium itakii n. sp. is distinguishable from Phorticium polycladum Tan and Tchang, 1976 based on the latter’s more rounded elliptical 2nd pseudo-concentric shell. The size ratio of the 2nd pseudo-concentric shell to the 1st pseudo-concentric shell is also different between these two species. It was measured as ca. 2.4 along the Lt-axis and 2.8 along the Pl-axis for Phorticium itakii n. sp. and as 1.8–2.0 along the Lt-axis and 1.9–2.3 along the Pl-axis for Phorticium polycladum .

Dimensions. Based on the holotype specimen. The length along the Lt-axis : 111.1 μm (2nd pseudo-concentric shell), 46.4 μm (1st pseudo-concentric shell); The length along the Pl-axis : 88.1 μm (2nd pseudo-concentric shell), 31.6 μm (1st pseudo-concentric shell); The size ratio of the 2nd pseudo-concentric shell to the 1st pseudo-concentric shell: ca. 2.4 along the Lt-axis and ca. 2.8 along the Pl-axis. The length ratio of the Fr-axis to the Pr-axis in Sg-view : ca. 1.3–1.4; Diameter of pores on the 1st pseudo-concentric shell: 4–7 μm; Diameter of pores on the 2nd pseudo-concentric shell: 10– 14 μm .

Figures

FIGURE 24. Photographs of the encountered morphotypes of Phorticium multispinum Popofsky, 1912 sensu emend. (1-3) and Phorticium itakii n. sp. (4-6). All are Pl-view at Type 1, Fr-view at Type 2. Scale bar equala 0.1 mm. All specimens are from YDY05-01.