Strongylacidon zanzibarense Lendenfeld, 1897

Calcinai, Barbara, Bavestrello, Giorgio, Bertolino, Marco, Pica, Daniela, Wagner, Daniel & Cerrano, Carlo, 2013, Sponges associated with octocorals in the Indo-Pacific, with the description of four new species, Zootaxa 3617 (1), pp. 1-61 : 15-16

Strongylacidon zanzibarense Lendenfeld, 1897

( Fig. 8 A–F)

Examined material. Sample Raja 071: Indonesia, Raja Ampat, Goss Over, 15 m, 2006.

Description. Massively encrusting sponge, about 2 mm thick; growing on Carijoa riisei colonies up to anthocodiae that remain free to expand and retract ( Fig. 8 A, B). The examined sample consists of a single portion of coral that is 6 cm long. Surface smooth, pierced by groups of pores visible without magnification ( Fig. 8 A–C). The sponge is mustard coloured in situ , with transparent subectosomal canals converging on elevated oscules ( Fig. 8 A). In ethanol the colour is uniformly light yellowish ( Fig. 8 B).

Skeleton. No specialized ectosomal skeleton, only a membranous peel covering the pulpy body. The choanosomal skeleton is plumose, with strongyles organized in multispicular tracts (25 – (66.8 ± 32.0) – 140 μm thick) reinforced with spongin ( Fig. 8 D). Numerous chelae and strongyles are also scattered among the tracts. Sand is present in low quantities in the sponge tissue and in the spicule tracts.

Spicules. Strongyles straight or slightly curved ( Fig. 8 E), 130 – (173.8 ± 38.3) – 225 x 2 – (2.4 ± 0.2) – 2.5 μm. Unguiferate anisochelae with three teeth splayed outwards and different in size on the two extremities ( Fig. 8 F), 10 – (12.3 ± 0.7) – 12.5 μm.

Distribution and remarks. This is the first record for Indonesia and the second after the original description from Zanzibar. The species was also observed in the Bunaken National Park (North Sulawesi) growing on pergamentaceous tubes of polychaetes (C.B. pers. observ.). Strongylacidon zanzibarense was originally described as an epibiont on the carapace of a crab ( Lendenfeld 1897) with a crust about 5–8 mm thick (van Soest 2002b).

Van Soest (2002b) noted that the holotype of S. zanzibarense possessed a reticulation of tracts of strongyles, reinforced by spongin, straight strongyles (160 – 260 x 3 – 4 μm) and peculiar unguiferate chelae (about 9 μm, from the image reported in van Soest 2002b: 526) that may be considered anisochelae, with different teeth on the opposite extremities. The Indonesian specimen fits with the species described by Lendenfeld especially in the size of the spicules and in the peculiar shape of the chelae. In our specimen the skeleton consists of strongyles organized in multispicular, plumose tracts; this organisation, different from that reported by van Soest (2002b) for the holotype, is probably due to the slenderness of our specimen (only 2 mm). It has been noted that the plumose, choanosomal skeleton of encrusting Strongylacidon specimens becomes reticulate in massive ones (van Soest 2002b).

Figures

FIGURE 8. Strongylacidon zanzibarense Lendenfeld, 1897. A, Sponge encrusting Carijoa riisei in situ; B, Close up of the sponge showing polyps clear of the sponge covering; C, Smooth surface pierced by groups of pores; D, Choanosomal skeleton organized in plumose, multispicular tracts; E, Strongyle; F, Unguiferate chela.