Characodoma protrusum

Characodoma protrusum (Thornely, 1905) (Fig. 16.1–6) Gemellipora protrusa Thornely, 1905: 119, fig. 7; Waters 1913: 506, pl. LXX, figs 4–6. Cleidochasma protrusum: partim Harmer 1957: 1040 (part), text-fig. 112, pl. LXXI, figs 2, 4, non pl. LXXI, figs 1, 3 (= Characodoma suluense (Soule, Soule & Chaney, 1991)); Hayward & Cook 1979: 89; Soule et al. 1991: 468, pl. 1, fig. 1, pl. 2, figs 1, 2;? d’Hondt & Mascarell 2010b: 320. Characodoma protrusum: Cook & Bock 1996: figs 12, 13. Material examined. SMF 11545 (3 specimens; St. 230 KD1; Fig. 16.3), SMF 40792 (St. 283 KU; Fig. 16.2, 16.4–6), SMF 40806 (St. 283 KU; Fig. 16.1). Description. Colony base encrusting, multiserial, unilamellar (Fig. 16.1); colonies becoming rigidly erect, multiserial, bilamellar, dichotomously branching (Fig. 16.2); transition from encrusting to erect growth not observed. Zooids arranged quincuncially, separated by broad and distinct furrows. Pore chambers not observed. Ancestrula and early astogeny not observed. Autozooids irregularly polygonal to subhexagonal (Fig. 16.3), 298–482 μm (ẋ = 381 ± 48 µm; CV = 13; N = 45 on 3 specimens) long by 221–385 μm (ẋ = 293 ± 42 µm; CV = 14; N = 45 on 3 specimens) wide. Frontal shield slightly convex, finely tuberculate, irregularly pierced by c. 20 circular (areolar) pores at the margins and proximally (Fig. 16.4). Orifice terminal, keyhole-shaped; anter subcircular, 84–123 μm (ẋ = 100 ± 8 µm; CV = 8; N = 45 on 3 specimens) long by 81–100 μm (ẋ = 89 ± 5 µm; CV = 6; N = 45 on 3 specimens) wide, separated by proximomedially directed condyles from the poster; poster trifoliate, with paired, variably developed indentations proximal to the condyles, well-rounded proximally, 33–52 μm (ẋ = 41 ± 4 µm; CV = 10; N = 45 on 3 specimens) long by 26–47 μm (ẋ = 34 ± 4 µm; CV = 13; N = 45 on 3 specimens) wide (Fig. 16.5). Spine bases not observed. Ovicells hyperstomial, globular, 105–150 μm (ẋ = 132 ± 13 µm; CV = 10; N = 45 on 3 specimens) long by 140–203 μm (ẋ = 172 ± 13 µm; CV = 7; N = 45 on 3 specimens) wide, acleithral; ectooecia finely tuberculate, evenly pierced by circular pseudopores (Fig. 16.4). Avicularia monomorphic (Fig. 16.5–6), adventitious, usually single, proximolateral to the orifice, second avicularium (if present) distolateral to the orifice, bilaterally symmetrical, dextral or sinistral, kite-shaped, 90–159 μm (ẋ = 122 ± 14 µm; CV = 11; N = 45 on 3 specimens) long by 75–124 μm (ẋ = 96 ± 10 µm; CV = 11; N = 45 on 3 specimens) wide. Avicularian aperture longitudinally elliptical, 54–99 μm (ẋ = 78 ± 10 µm; CV = 13; N = 45 on 3 specimens) long by 38–78 μm (ẋ = 60 ± 7 µm; CV = 12; N = 45 on 3 specimens) wide; crossbar complete, at about half the avicularian length. Rostrum rounded, slightly elevated, proximally directed. Kenozooids not observed. Remarks. Characodoma protrusum (Thornely, 1905) was revised by Soule et al. (1991), who also provided images of the type material. The specimens from the Gulf of Aden closely resemble both this material and additional colonies imaged by Cook & Bock (1996) from Wasini Island, Kenya. However, in the Aden specimens, the trifoliate shape of the poster varies, with indentations proximal to the condyles being inconsistently pronounced and sometimes partially obscured (Fig. 16.3). Despite these minor differences, the Aden specimens are clearly conspecific with Characodoma protrusum, extending the species’ known range into the northwestern Indian Ocean. Characodoma protrusum has been reported from multiple regions of the Indian Ocean and was also described from the Marquesas Islands, French Polynesia, by d’Hondt & Mascarell (2010b). However, as no images of the Pacific material were provided, its conspecificity with the Indian Ocean populations remains uncertain. Soule et al. (1991) excluded specimens from the Sulu Sea (North Ubian Island, Philippines) from Characodoma protrusum, and instead described Characodoma suluense, which differs primarily in its kidney-shaped poster lacking indentations, and a frontal shield with fewer areolae. Characodoma biavicularium (Canu & Bassler, 1929) from the Sibuyan Sea near Romblon, Philippines, is distinguished by the presence of a second, smaller, proximally positioned avicularium, and both avicularia types in this species are elliptical.