Flabellopora lingua Silén, 1947a

(Fig. 47; Table 42)

Flabellopora lingua Silén, 1947a: 47, text-figs 36, 37, pl. 2, fig. 13.

Material examined. Holotype by monotypy UPSZTY 2221, Okinoshima, Kiuschin, Japan. Leg. Prof. S. Bock 1914.

Description. Colony rooted, flat, leaf-shaped, bilaminar with zooids and avicularia opening on both surfaces.

Autozooids indistinct, arranged in alternating series; calcification of the frontal shield smooth and with coarse, rounded tubercules (diameter 25–120 µm) occurring among the apertures and the avicularia (Fig. 47A); tubercles at the edge of the colony pointed and sharp (Fig. 47C).

Orifice subcircular, proximal margin with two robust, rounded triangular condyles (height c. 14–25 µm, base c. 27–35 µm) and a narrow, V- or U-shaped sinus (20–30 µm deep by 15–25 µm wide) (Fig. 47C, E); each orifice surrounded by a short, circular peristome appearing as a smooth, narrow (c. 10–15 µm wide), raised, slightly flared rim (Fig. 47B). An adapical elliptical pore present medially to each aperture, 8–10 µm long by 15–20 µm wide.

Avicularia of two types: type 1 small, interzooidal/adventitious, arranged in undulate series between zooidal rows, such that each zooidal aperture is surrounded by six avicularia, ovoidal with slightly raised, semicircular or ogival rostrum directed distally, mandible semicircular, crossbar complete (Fig. 47A, B, E); type 2 interzooidal/ vicarious, obliquely or horizontally placed along the lateral edges of the colony forming a continuous series, highly variable in size but always larger than those scattered among zooidal apertures, teardrop- or pear-shaped with rounded triangular raised rostrum, mandible of the same shape, and complete crossbar (Fig. 47B–D); two circular septular pores, c. 15 µm in diameter, flanking each avicularium (Fig. 47B, E).

Ovicells absent.

Remarks. SEM images of a subsample of this holotype, bleached and coated, were taken by Gerhard C. Cadée in 1991 but never published. New images of the same fragment were also taken specifically for this study, some of which are available in Fig. 47.

Silén (1947a) excluded both that this species was lying flat on the bottom because of the bilamellar nature of its colony, and that it was standing on the bottom balanced on one of its edges because of its flatness and thinness. He hypothesized that the colony would hang down from the very thin and delicate chitinous tube, about half a cm long, observed emanating from the apical margin of the colony (see Silén 1947a, pl. 2, fig. 13). The tube was supposed to be attached to a foreign substrate. In some species of Flabellopora however roots are more numerous and have a support function (Bock & Cook 2004). For instance, Harmer (1957) observed and described multiple delicate rootlets originating from lunate pores in the adapical region of Flabellopora irregularis Canu & Bassler, 1929 . Hirose (2017, fig. 24.3g) illustrated a colony of Flabellopora sp. from Okinawa living at 46 m depth supported above the sandy seafloor by four roots. Thus, it is also rather likely for the colonies of F. lingua to be standing upright on the seafloor, anchored by one or more rootlets to the particulate substratum.