Exechonella similis Cáceres-Chamizo, Sanner, Tilbrook & Ostrovsky, 2017

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 : 216

Exechonella similis Cáceres-Chamizo, Sanner, Tilbrook & Ostrovsky, 2017

( Fig. 6E, F )

Exechonella similis Cáceres-Chamizo et al., 2017, p. 43 , fig. 17.

? Exechonella brasiliensis: Winston & Heimberg 1986, p. 15 , figs 26–27.

Exechonella brasiliensis: Tilbrook et al. 2001, p. 65 , fig. 8g.

Material examined. VNMN-0226 (CT-24), on SEM stub.

Measurements. AzL, 0.78–1.09 (0.930 ± 0.094); AzW, 0.52–0.80 (0.670 ± 0.074) (n = 15, 1). OrL, 0.18–0.21 (0.198 ± 0.012); OrW, 0.19–0.21 (0.203 ± 0.006) (n = 7, 1).

Description. Colony encrusting, unilaminar, sheet-like.

Zooids large, hexagonal, delineated by groove. Frontal shield convex, with minute areolae; perforated with 19–36 (29.7 ± 4.0; n = 13) foramina, each with smooth, raised rim. Orifice on average about as wide as long; with low, rounded condyles slightly proximal to middle; poster as wide as anter or nearly so, rounded-quadrate. Raised peristome surrounding orifice, slightly flared, smooth inside, pustulose outside, not obscuring orifice; often with low, blunt projection on proximal rim. Lateral-most foramen on one or both sides larger than rest, converted to avicularium, scarcely differentiated externally from other foramina.

Oral spines, ooecia lacking.

Remarks. Cáceres-Chamizo et al. (2017) described this species in detail, with excellent illustrations. Average zooid size at Co To (AzL × AzW, 0.93 × 0.67 mm) is larger than presented in the original description (0.78 × 0.62 mm), but the number of frontal foramina is similar (19–36 at Co To vs 21–36 originally described). The original description states that the orifice is wider than long, but this is scarcely reflected in the accompanying measurements (OrL × OrW, 0.19 × 0.20 mm), and not at all at Co To (0.20 × 0.20 mm).

Distribution. The type locality is Lizard Island, Great Barrier Reef; this species is also known from Vanuatu ( Cáceres-Chamizo et al. 2017). The previously known latitudinal range was 14– 15°S; the Co To record extends the range northward nearly to 21°N.

Figures

FIGURE 6. A–D. Trypostega henrychaneyi Tilbrook, 2006, VNMN-0225. A. Autozooids and distal zooeciules. B. Zooid with ooecium (right). C. Enlargement showing orifice and zooeciule. D. Colony margin, showing zooeciule extending to basal surface. E, F. Exechonella similis Cáceres-Chamizo, Sanner, Tilbrook & Ostrovsky, 2017, VNMN-0226. E.Autozooids. F. Enlargement showing orifices. Scale bars: A, 200 µm; B, C, 50 µm; D, 100 µm; E, 500 µm; F, 150 µm.