Monanchora enigmatica (Burton & Rao, 1932)

(Fig. 9 A–E)

Examined material. Sample Bugor 410 (bis1): Indonesia, North Sulawesi, Siladen Island, 27 m, September 2007.

Description. Fleshy, thin sponge, about 1 mm thick, covering the body wall of Carijoa riisei (Fig. 9 A). The sample occurs on two fragments of the octocoral, about 6 cm in length, which are branched and covered by additional epibionts (Fig. 9 A). Macroscopically smooth surface, yellowish in ethanol (Fig. 9 A).

Skeleton. Without a definite ectosome. Choanosomal skeleton of multispicular tracts of strongyles, partially embedded in spongin, running towards the surface, and interconnecting, in a confused way, in the interior parts (Fig. 9 B). These tracts are echinated by styles (Fig. 9 C).

Spicules. Strongyles straight (Fig. 9 D), 172.5 – (186.8 ± 9.8) – 207.5 x 2 – (2.5 ± 0.3) – 2.5 μm. Styles slightly constricted beneath the rounded extremity and with a pointed tip (Fig. 9 E), 77.5 – (140 ± 25.4) – 162 x 2.5 – (6.3 ± 1.8) – 7.5 μm. No microscleres.

Distribution and remarks. This is a new record for the Indonesian Archipelago and the second after its original description from the Nicobar Islands. In his revision of Monanchora, van Soest (2002c) stated that the assignment to this genus is uncertain for species having only reduced and modified megascleres. This is the case for M. enigmatica, which lacks microscleres and possesses modified megascleres (strongyles). Nevertheless the species is well characterised by its spicular complement of strongyles and styles with a characteristic “constricted neck” (177.2 x 2.6 and 128.9 x 5.6 μm, respectively) and by a “plumose dendritric skeleton of bundles of thin strongyles” echinated by styles (van Soest 2002c). The skeleton arrangement previously described (Fig. 9 B, C) and the spicular features of our specimen (Fig. 9 D–F) fit with those of the Indian species of Burton & Rao (1932), re-described by van Soest (2002c). This species was also recorded in massive form, incorporating and overgrowing vermetid tubes, close to the sampling locality (B.C. pers. observ.).