Rhabdastrella distincta (Thiele, 1900)

Calcinai, Barbara, Bastari, Azzurra, Bavestrello, Giorgio, Bertolino, Marco, Horcajadas, Santiago Bueno, Pansini, Maurizio, Makapedua, Daisy M. & Cerrano, Carlo, 2017, Demosponge diversity from North Sulawesi, with the description of six new species, ZooKeys 680, pp. 105-150 : 108-110

Rhabdastrella distincta (Thiele, 1900) Figure 5

Coppatias distinctus Thiele, 1900: 56.

Material examined.

BU-560, 26/06/2004, Bualo (Bunaken Island), unknown depth. BU-575, 27/06/2004, Alung Bauna (Bunaken Island), 27 m depth.

Description.

The sponge has a massive and irregular shape, a large size, up to 50 cm in diameter, and was exclusively found partially covered by Amphimedon cf. sulcata (see below). In the part not covered by the epibiotic sponge, R. distincta is yellow-lemon (Fig. 5A), or dark green (Fig. 5B), turning black when cut or preserved. Wide oscular areas are often evident (Fig. 5A, B).

Skeleton. Spherasters are located in the outer part of the sponge, but do not form a real cortex (Fig. 5C, D). The choanosomal skeleton consists of scattered oxeas which tend to form radial tracts towards the peripheral part (Fig. 5C). Oxyasters and oxyspheraster are dispersed in the choanosome.

Spicules. Megascleres are fusiform oxeas (Fig. 5E) with rather sharp tips, 720 - (832.5 ± 65.7) - 990 × 10 - (13.3 ± 2.9) - 20 µm. Microscleres are spherasters of variable size, 12.5 - (29.5 ± 6.4) - 35 µm in diameter (Fig. 5F), with a large centre and thick rays with sharp or bifurcated tips; oxyasters (Fig. 5G) with small centre and thin rays, 35 - (49 ± 8.1) - 65 µm in diameter; oxyspherasters with well-developed centre (Fig. 5H), 10 - (15.1 ± 2.6) - 20 µm.

Remarks.

The Indonesian specimens fit with the description of R. distincta in having the same skeletal organisation (characterised by oxeas scattered in the inner part of the sponge and radially arranged close to the surface), absence of triaenes, spherasters in the peripheral part, oxyasters and oxyspheraster scattered in the choanosome. Spicule sizes are comparable to those of the type species that are fusiform oxeas of 850 × 25 µm, spherasters up to 40 µm, oxyasters up to 80 µm and oxyspherasters of 15 µm (see Uriz 2002). The principal difference with Thiele’s original description is that smooth microscleres were not observed and a real cortex is not detectable in the studied specimens.

This is the first record of the species since the original description of Thiele (1900) based on two specimens from Ternate, Indonesia.

Remarks on the association.

See below.