Hippopodina adunca Tilbrook, 2006

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 : 223-224

Hippopodina adunca Tilbrook, 2006

( Fig. 10A )

Hippopodina adunca Tilbrook, 2006, p. 248 , pl. 54C, D, and synonyms therein.

Hippopodina adunca: Dick & Grischenko 2017, p. 211 , fig. 24a, b.

Material examined. VNMN-0239 (CT-17), on SEM stub; VNMN-0240, two colony fragments.

Measurements. AzL, 0.73–1.00 (0.850 ± 0.080); AzW, 0.56–0.84 (0.670 ± 0.079); OrL, 0.24–0.26 (0.248 ± 0.008); OrW, 0.19–0.24 (0.213 ± 0.015) (n = 15, 1). OrL, ooeciate zooid, 0.224; OrW, ooeciate zooid, 0.263 (n = 1). OvL, 0.602; OvW, 0.619 (n = 1).

Description. Colony encrusting, sheet-like, unilaminar but occasionally bilaminar due to self-overgrowth.

Zooids large, rectangular, delineated by groove. Frontal wall convex, perforated by numerous tiny pseudopores. Orifice hoof-shaped; poster same width as anter or slightly narrower, separated by sharp condyles; proximal margin of orifice straight or markedly concave. Orifices dimorphic, with those of ooecium-bearing zooids wider than those of zooids lacking ooecia.

Adventitious avicularia usually paired, sometimes single; each with large chamber lateral to orifice, rostrum long, tapering, directed distomedially and slightly curving around distal end of orifice, crossbar complete.

Ooecium prominent, resting on frontal wall of next-distal zooid; circular in outline, perforated over entire surface with tiny pseudopores. Spines lacking.

Remarks. The large avicularia having setiform mandibles directed distomedially are typical of H. adunca , which, however, also typically has the proximal margin of the orifice straight. While some zooids in the specimens from Co To have the proximal orificial margin nearly straight, most have a concave, distinctly rounded margin. In addition, the only ooeciate zooid observed has a sharp, raised suboral collar. A key character that helps differentiate among Hippopodina species is the ancestrular complex, which forms a triad in in some species (including H. adunca ) but a tetrad in others ( Tilbrook 1999, 2006). No ancestrular complex was found in the Co To specimens.

Distribution. Broadly distributed in the Indo-West Pacific, ranging from Mauritius westward to Fiji ( Tilbrook 2006) and northward as far as Okinawa, Japan ( Dick & Grischenko 2017).

Figures

FIGURE 10. A. Hippopodina adunca Tilbrook, 2006, VNMN-0239, autozooids, with one ooecium. B–D. Calloporina sigillata Canu & Bassler, 1929, VNMN-0242. B. Colony. C. Autozooid with ooecium. D. Ancestrula (bottom right) and periancestrular zooids. Scale bars: A, 500 µm; B, 1 mm; C, 250 µm; D, 500 µm.