Antropora minor (Hincks, 1880)

Judith L Winston, 2016, Bryozoa of Floridan Oculina reefs, Zootaxa 4071 (1), pp. 1-81 : 20-21

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.

Figures

FIGURE 10. Antropora minor (Hincks, 1880): A, pluriserial much abraded colony; B, group of autozooids and closed zooids; C, another group of zooids, showing how frontal membrane becomes calcified by repeated episodes of grazing and regeneration; D, two autozooids and a kenozooid; E, a group of zooids with open to completely calcified frontal membranes; F, close-up of three zooids with various degrees of frontal-wall calcification. Scale bars: A, 1 mm; B, C, E, 0.5 mm; D, 0.2 mm; F, 0.3 mm.

Tables

TABLE 9. Measurements in mm of Antropora minor (Hincks, 1880).

	Lz	Wz	Lo	Wo	Lcircz	Wcircz
N	18	18	18	18	18	18
Mean	0.381	0.251	0.041	0.061	0.257	0.211
SD	0.040	0.024	0.007	0.008	0.037	0.025
Min	0.324	0.216	0.036	0.054	0.216	0.162
Max	0.450	0.306	0.054	0.072	0.324	0.252