Oceanapia fistulosa (Bowerbank, 1873)

(Fig. 35 A–H)

Examined material. Sample Bugor 514: Indonesia, North Sulawesi, Bunaken Island, Pangalisang, 25 m, 11 September 2007.

Description. Massive sponge, with ovoid or spherical body; the sponge lives completely buried in the sediment, with only fistular chimneys above the substrate surface. Inhalant closed fistules with short, apical digitations; only fistules were collected; they are up to 17 cm high, with a diameter about 0.5–2 cm (Fig. 35 A–C). In the area of the Bunaken National Park the fistules of this sponge were frequently observed covered by the octocoral Alertigorgia hoeksemai (Fig. 35 A, C), which was obscuring the sponge below. The colour of the fistules is vivid pink (Fig. 35 A), pale yellowish in ethanol (Fig. 35 B).

Skeleton. Only the fistular skeleton was examined. The ectosome is a tangential reticulum of oxeas; the surface is microhispid due to groups of oxeas piercing it at the nodes (Fig. 35 D). The ectosomal skeleton is supported by ascending tracts opening in irregular fans (Fig. 35 E). The internal surface of the hollow fistules is supported by longitudinal, thick parallel tracts of oxeas (Fig. 35 E). In the fistular areas covered by the octocoral, the sponge skeleton appears modified as the ascending tracts, opening in fans and supporting the tangential ectosomal skeleton, are not present (Fig. 35 F).

Spicules. Oxeas of usual shape, in two size classes: oxeas I (Fig. 35 G), 210 – (242.6 ± 12.9) – 260 x 10 – (10.9 ± 1.2) – 12.5 µm; oxeas II (Fig. 35 H), 82.5 – (90.5 ± 5.6) – 102.5 x 3.5 – (4.5 ± 0.6) – 5 μm. Small and thin oxeas, probably growing forms, are also present.

Distribution and remarks. Australia (Ridley 1884), Indonesia (Topsent 1897) and Indian Ocean ( Dendy 1922). This species is very common in the Bunaken National Park (Bavestrello et al. 2002; Cerrano et al. 2007).