Tetracyclus radius Saito-Kato, Hayashi & Tanimura, 2011

Saito-Kato, Megumi, Hayashi, Tatsuya & Tanimura, Yoshihiro, 2011, Tetracyclus radius (Bacillariophyta) a new fossil species from Miocene freshwater sediments in the Japan Sea, Phytotaxa 24, pp. 51-57 : 52

Tetracyclus radius Saito-Kato, Hayashi & Tanimura , sp. nov. ( Figs 1—20 ).

Type: — JAPAN. Deep-sea sediments at the earliest Middle Miocene , 490 cm in depth of the RC12-394 core, recovered from the Yamato Bank, Japan Sea (holotype MPC-04211) .

Vegetative cells: Valves circular, 10–30 µm in diameter, striae density c. 25–30 in 10 µm at margin on valve face; c. 30 areolae in 10 µm, arranged radially. Valve face flattened, mantle vertical. Valve face with central hyaline area, lacking sternum; valve face and margin with internally developed radial transapical ribs and striae. Some ribs extending towards central area, some part way onto valve face, others present only at mantle. Striae composed of parallel rows of areolae. Single rimoportula, simple slit externally, located within stria, with paired lips, internally. Cingulum composed of more than 5 open copulae, band orientation at 90 o to rimoportula. Each copula with ligula and paired areolae divided by septum; areolae in parallel rows. No evidence of further band differentiation.

Initial cells: Hemispherical with thin valve margin, 25–30 µm in diameter. Central area with irregularly arranged areolae and hyaline structures. Marginal area composed of internally developed radial costae and striae. Striae composed of parallel areolae rows, single rimoportula located within stria, structure as in vegetative valve.

Figures

FIGURES 1–10: Tetracyclus radius. Figs 1–3: LM images of holotype specimen at different focal depths. Arrow indicates position of rimoportula in Fig. 2. Figs 4–7: LM images of further specimens from the same horizon as holotype. Fig. 4 is the frustule in girdle view, Figs 5–7: Initial cell at different focal depths. Fig. 7: Valve with rimoportula arrowed. Figs 8–10: SEM images of specimens from the same horizon as holotype. Fig. 8: Valve with external opening of rimoportula (arrow). Fig. 9: Valve and part of the girdle, with 5 bands. Fig. 10: Partial cingulum showing opening and ligula (arrows). All scale bars = 10 µm.

FIGURES 11–16: Tetracyclus radius. SEM images of specimen from the same horizon as holotype. Fig. 11: Internal view of valve. Figs 12–16: Various higher magnification images of the valve in Figure 11 (numbers on Figure 11 indicate area in Figs 12–16). Rimoportula on valve face/mantle junction (Figs 12 & 14, indicated by black arrows); open valvocopula with striae and septa (Figs 13–16, white arrows indicate the septum). Scale bars: Figs 11 & 12: 5 µm; Figs 13–16: 3 µm.

FIGURES 17–20: Tetracyclus radius. SEM images of specimens from same horizon as holotype specimen. Figs 17 & 18: Internal and oblique view of same valve; note rimoportula on mantle (arrows). Fig. 19: Valve with rimoportula on valve face near the central area (arrow). Fig. 20: Initial valve. Note sessile labium of rimoportula (arrow). Scale bars: Figs 17 & 18: 3 µm; Fig. 19: 5 µm; Fig. 20: 10 µm.