Plesiocleidochasma porcellaniforme ( Soule, Soule & Chaney, 1991b )

Dick, Matthew H., Ngai, Nguyen Danh & Doan, Hung Dinh, 2020, Taxonomy and diversity of coelobite bryozoans from drift coral cobbles on Co To Island, northern Vietnam, Zootaxa 4747 (2), pp. 201-252 : 232

Plesiocleidochasma porcellaniforme ( Soule, Soule & Chaney, 1991b)

( Figs 14 , 20G )

Schedocleidochasma porcellaniforme Soule, Soule & Chaney, 1991b, p. 481 , pl. 1, fig. 1, pl. 5, figs 3, 4, and synonyms therein.

Schedocleidochasma porcellaniforme: Tilbrook et al. 2001, p. 98 , fig. 21A, B; Liu et al. 2001, 705, pl. 79, figs 1–3; Tilbrook 2006, p. 293, pl. 64B.

Cleidochasma porcellanum (Busk) : Winston and Heimberg 1986, p. 34, figs 85–87.

Material examined. VNMN-0256 (CT-7), VNMN-0257 (CT-8), VNMN-0258 (CT-13), VNMN-0259 (CT-15), VNMN-0260 (CT-29), VNMN-0261 (CT-31), on SEM stubs.

Measurements. AzL, 0.37–0.47 (0.403 ± 0.025); AzW, 0.22–0.39 (0.306 ± 0.041) (n = 15, 1). OrL, 0.11–0.15 (0.131 ± 0.010); OrW, 0.089 –0.115 (0.099 ± 0.007) (n = 15, 2). OvL, 0.17–0.22 (0.194 ± 0.015); OvW, 0.19–0.25 (0.221 ± 0.015) (n = 15, 1).

Description. Colony unilaminar, encrusting, sheet-like; sometimes partly bilaminar due to self-overgrowth.

Zooids small, boundaries indistinct. Frontal wall slightly convex, imperforate; surface weakly pustulose; often bearing several scattered, low, rounded nodules; with a few marginal pores, some of which may be positioned inside margin. Marginal zooids show three small spine bases, which are not evident in interior zooids. Orifice keyhole-shaped; anter circular or subcircular, separated by strong, proximomedially directed condyles from narrower, rounded poster.

Frontal avicularia single or paired lateral or proximolateral to poster, although zooids lacking frontal avicularia not uncommon. When paired, avicularia directed at slightly different angles, one sometimes pointing laterally and other distolaterally. Avicularian rostrum rounded proximally, acute distally; crossbar complete or incomplete; opesial opening more or less arrowhead-shaped.

Ooecium subimmersed, imperforate, same texture as frontal wall; opening covered by broad, flat labellum, with narrow transverse slit above, distinct lateral slits, and narrow transverse slit below that merges with lateral slits.

Remarks. This species was originally placed in the genus Schedocleidochasma Soule, Soule & Chaney, 1991b , but Berning (2012), concluding that no clear boundary could be drawn between that genus and Plesiocleidochasma , declared the former a junior synonym of the latter.

Distribution. Widely distributed in the central to western Pacific, ranging from the Hawaiian Islands westward to Indonesia, Thailand, Vietnam, and the Maldives (Indian Ocean) ( Soule et al. 1991b; Tilbrook 2006; this study).

Figures

FIGURE 14. Plesiocleidochasma porcellaniforme Soule, Soule & Chaney, 1991. A. Colony, VNMN-0256. B. Autozooids at colony margin, VNMN-0258. C.Autozooids with and without ooecia near colony margin, VNMN-0257. D. Enlargement showing orifice shape, VNMN-0257. Scale bars: A, 1 mm; B, C, 250 µm; D, 150 µm.

FIGURE 20. Competitive interactions between bryozoans and the encrusting foraminiferan Planorbulina larvata. A. P. larvata forming stand-off with Scorpiodinipora costulata (upper part) and overgrowing the latter (lower part), VNMN-0254. B. P. larvata overgrowing Antropora minor, VNMN-0218. C. P. larvata overgrowing Torquatella imperforata, VNMN-0252. D. Founding chamber of P. larvata settled on margin of Parasmittina parsevalioidea colony, VNMN-0231. E. Stand-off between P. larvata and Scorpiodinipora costulata, VNMN-0254. F. P. larvata settled on Disporella phaohoa n. sp. colony, VNMN-0256. G. P. larvata settled on Plesiocleidochasma porcellaniforme, VNMN-0256. H. Metroperiella cotoensis n. sp. beginning to overgrow P. larvata, VNMN-0238. Scale bars: D, 150 µm; all others, 1 mm.