Stelletta tethytimeata Calcinai, Bastari, Bertolino & Pansini

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

Stelletta tethytimeata Calcinai, Bastari, Bertolino & Pansini sp. n. Figure 4

Material examined.

Holotype: MSNG 60136, BU-289, 17/05/2001, Raymond’s Point (Bunaken Island), unknown depth. Paratype: MSNG 60137, BU-562, 26/06/2004, Bualo (Manado Tua Island), unknown depth.

Other material.

BU-533, 21/06/2004, Bualo (Manado Tua Island), about 8 m depth. BU-545, 23/06/2004, Raymond’s Point (Bunaken Island), about 20 m depth. BU-98, 23/03/2000, Lekuan II (Bunaken Island), 5 m depth.

Diagnosis.

Massively rounded yellow sponge; the colour changes after fixation. Megascleres are anatriaenes with characteristic bending and a single type of oxeas; microscleres are represented by a heterogeneous set of tylasters and oxyasters.

Description.

The sponge is light yellow-lemon in vivo (Fig. 4A); the colour changes in the preserved specimens, becoming dark-brown to blackish. It is almost totally covered by the associated epibiotic species T. tylota (see above), with the exception of the oscula that, protruding from the surface of T. tylota , are clearly distinguishable for their different colour (Figs 3A, 4A). Since the external sponge T. tylota is thinly encrusting, most of the mass of the associated sponges is due to S. tethytimeata sp. n. that can be as large as 10 cm across (Fig. 4A, B).

Skeleton. The cortex is a collagenous layer 400-700 µm thick (Fig. 4B); the triaenes have their clades tangential to the surface and sometimes protrude from it (Fig. 4C), merging in the tissue of the epibiotic T. tylota . The choanosomal skeleton is formed by tracts of oxeas without a clear radial arrangement with microscleres scattered in between (Fig. 4D). Towards the sponge surface, the spicule density lowers and oxeas are more or less parallelly arranged (Figs 3C, 4B, D).

Spicules. Megascleres are anatriaenes (Fig. 4E), with straight, sharp-pointed rhabdome of 570 - (708.2 ± 119.3) - 800 × 10 - (15.7 ± 3.8) - 22.5 µm and clads of 80 - (113.4 ± 43.3) - 225 × 7.5 - (9.0 ± 2.6) - 12.5 µm with sharp tips and characteristic bending. Oxeas straight, fusiform, with sharp tips (Fig. 4F), sometimes modified into styles; they measure 1274 - (1514.5 ± 145.3) - 1950 × 20 - (24.5 ± 3.9) - 30 µm. Microscleres encompass a heterogeneous set of tylasters and oxyasters (Fig. 4G), with 4-9 rays, with spines along the rays or grouped at the extremities 20 - (27.2 ± 4.4) - 35 µm.

Etymology.

The name refers to the association with Tethytimea tylota .

Remarks.

Stelletta tethytimeata sp. n. is characterised by one type of triaenes and by a single category of oxeas. Out of the 146 species of Stelletta , distributed in all the oceans ( van Soest et al. 2016), 49 are from the tropical Indo-Pacific area ( van Soest 1994). However, they all differ from the new species in colour, skeletal organisation and especially in the spicule features. They show different categories of megascleres (oxeas of different sizes, plagio-, orto- and dico-triaenes) and microscleres. In particular, 10 species of the tropical Indo-Pacific Stelletta species present a single type of triaenes: S. bocki Rao, 1941, S. brevioxea (Pulitzer-Finali, 1993) and S. cavernosa (Dendy, 1916) have ortotriaenes; S. brevis Hentschel, 1909, S. centroradiata Lévi and Lévi, 1983, S. centrotyla Lendelfeld, 1907 and S. herdmani Dendy, 1905 have plagiotriaenes; S. herdmani var. robusta Thomas, 1979 has protriaenes, whereas S. hyperoxea Lévi and Lévi, 1983, S. vaceleti ( Lévi and Lévi, 1983), S. phialimorpha Lévi, 1993 and S. digitata (Pulitzer-Finali, 1993) have dicotriaenes. Actually, Stelletta tethytimeata sp. n. is the only species of the genus in this area possessing anatriaenes (peculiar for the characteristic clad bending) and a single category of oxeas. It is therefore justified, based on the five specimens in association with Tethytimea tylota encountered in this region, to erect a new species.

Remarks on the association.

The associated specimens of T. tylota and S. tethytimeata are flat or cushion-shaped with big, rounded lobes and wide oscular structures (Figs 3A, 4A).

By superficial analysis, the two associated species could appear as a single large individual sponge. The external species ( T. tylota ) can be detached with difficulty from the internal one ( S. tethytimeata sp. n.); the contact area may be observed in SEM images (Fig. 3C) and by histological preparations where the presence of a thin collagen layer of separation between the two species is detectable (Fig. 4B, H). Histological preparations clearly show the presence of the cortex of S. tethytimeata sp. n. made by a collagen layer up to 700 µm thick (Fig. 4B, H). In the cortex, collencytes are clearly visible and pigmentary cells are numerous (Fig. 4H).

The two associated species are quite common in North Sulawesi, always in association, generally in dim-light conditions, at a maximum depth of 20 m.