Antropora minor (Hincks, 1880)

(Fig. 10; Table 9)

Membranipora trifolium var. minor Hincks, 1880: 87, pl. 9, fig. 6.

Membrendoecium parvus Canu & Bassler, 1928a: 61, pl. 1, figs 1–2.

Membrendoecium minus: Marcus 1937: 50, pl. 9, fig. 22A, B.

Antropora minor: Tilbrook 1998: 34, fig. 2A–F; Vieira et al. 2008: 14; Winston et al. 2014: 151, fig. 7.

Material examined. VMNH no. 70609, 70610; USNM no. 1283235.

Description. Colonies encrusting, unilamellar, on calcareous substrata (Fig. 10 A). Zooids oval to subtriangular, broader proximally. Frontal membrane underlain by beaded cryptocyst and rimmed by proximally elongated gymnocyst (Fig. 10 B). Cryptocystal shelf also broader proximally, gradually narrowing to distal wall around half-moon shaped operculum and forming oval to bell-shaped opesia. Interzooidal avicularia interspersed between autozooids, each with circular foramen, granular cryptocyst and well-developed gymnocyst that may have a small tubercle (Fig. 10 B, C); mandible U-shaped, rostral rim well calcified. Brooding zooids show thickened lunate rim of calcification distally.

`Remarks. The most unusual feature of this species is its ability to calcify over the frontal membrane and opesia of many zooids in a colony (Fig. 10 E, F). In some zooids a small central opening may remain. In others the entire frontal surface is covered by concentric rings of calcification. These ‘closure plates’ may be a way to protect zooids from predation (colonies on Oculina showed a considerable amount of damage and repair), or a means to preserve nutritive resources in a food-scarce habitat.

Distribution. Oculina banks, Atlantic coast of Florida, Brazil.