Metroperiella montferrandi (Audouin, 1826)

Metroperiella montferrandi (Audouin, 1826)

Figure 33 View FIGURE 33

v. 1826 Flustra montferrandi Audouin , p. 240. v. 1890 Lepralia acuta Ortmann , p. 41, pl. 3, fig. 12.

v. 1957 Codonellina montferrandii (Audouin) ; Harmer, p. 1049, pl. 69, figs. 25–26, 30. v. 1975 Codonellina montferrandii (Audouin) ; Hayami, pl. 17, fig. 8.

v. 1984 Codonellina montferrandii (Audouin) ; Gordon, p. 77, pl. 26A.

v. 2001 Metroperiella montferrandii (Audouin) ; Tilbrook, Hayward and Gordon, p. 74, fig. 15F.

v. 2006 Metroperiella montferrandii (Audouin) ; Tilbrook, p. 182, pl. 39D.

Figured material. PMC EDM-Collection J.H.B.134a, sample 19227; Core 19, Daidokutsu cave, Okinawa, Japan, Holocene.

Description. Colony encrusting, multiserial, unilaminar. Autozooids distinct, separated by thick (13–23 µm) rims of smooth calcification outlining each perimeter and a thin furrow in-between, elongate, almost twice as long as wide (mean ZL/ZW 1.83), arranged in longitudinal rows. Frontal shield flat, nodular, evenly and densely pierced except for a narrow (c. 20–40 µm) band extending between margin of orifice and avicularium; pseudopores circular, 5–10 µm in diameter. Orifice terminal, raised relative to the frontal shield, ovoidal with horseshoe-shaped anter and a slightly narrower, shallow, bowl-shaped poster; condyles robust, rounded triangular, 12–24 µm long by 9–17 µm wide. Avicularia adventitious, typically one per zooid or occasionally absent, placed proximally to orifice along zooidal midline or slightly to either side, raised compared to the frontal shield; rostrum acutely triangular directed proximally; crossbar complete; distal opening semicircular, proximal opening rounded triangular. Ovicell hyperstomial, globular; ooecium smooth, wider than long, 185 µm long by 320 µm wide, perforated by circular pseudopores, slightly larger than those on the frontal shield (10– 20 µm in diameter), except for a narrow imperforate proximal band; the periphery of the single ooecium observed with incipit of secondary calcification produced by distal zooid.

Measurements (µm). ZL 653±61, 579–776 (1, 9); ZW 357±39, 280–414 (1, 9); OL 171±6, 165–183 (1, 7); OW 150±6, 141–161 (1, 7); AvL 129±14, 105–159 (1, 13); AvW 65±5, 57–73 (1, 13).

Remarks. Based on the available records, Metroperiella montferrandi appears to have a circumtropical distribution. Instances of its presence have been already documented in Japan, including both Recent (Ortmann, 1890; Harmer, 1957; Hirose, 2010) and Pleistocene (Hayami, 1975) occurrences. Within the limited size of the fragments examined here, the avicularia consistently are acutely triangular, with no observation of the spatulate form. It remains uncertain whether the absence of spatulate avicularia is genuine or due to the small size of the specimens. Specimens identified as M. montferrandi from Vanuatu ( Tilbrook et al., 2001) and the Kermadec Ridge (Gordon, 1984) also lack spatulate frontal avicularia. Among Metroperiella species with monomorphic avicularia of acute triangular shape, M. cotoensis Dick, Ngai and Doan, 2020 differs in having a deeper orifice poster, while M. agassizi Winston and Woollacott, 2009 has a narrower poster and longer avicularia, which are more asymmetrically placed.