Hymedesmia (Hymedesmia) rissoi Topsent, 1936

Bertolino, Marco, Cerrano, Carlo, Bavestrello, Giorgio, Carella, Mirco, Pansini, Maurizio & Calcinai, Barbara, 2013, Diversity of Porifera in the Mediterranean coralligenous accretions, with description of a new species, ZooKeys 336, pp. 1-37 : 12-13

Hymedesmia (Hymedesmia) rissoi Topsent, 1936 Figs 11 A–D

Hymedesmia gracilisigma var. rissoi Topsent, 1936: 35.

Material examined.

Specimen IG-F-BL3-F18b-spA; Specimen IG-F-BL4-sp9-sciaf.; specimen IG-F-BL4 sp11-fot.; alcohol preserved, Gallinara Island (station 2, Falcon ara) 44°01'22"N, 8°13'34"E, depth 35 m, collected on 17-06-2009; specimenSSS-BL1-sp11-sciaf.; Santo Stefano Shoals, (station 1), 43°49'N, 7°54'E, depth 35 m, collected on 14-02-2008.

Description.

Small (0.5 cm2), slimy, coriaceous encrusting sponge, grey in colour after alcohol preservation, recorded both on the surface and inside the coralligenous blocks.

Skeleton. Not observed.

Spicules. Megascleres: straight or slightly sinuous anisotornotes, sometimes modified in anisotylotes or strongyles (Fig. 11A), 140 (175) 177.5 × 2.5 (2.7) 3.75 μm; acanthostyles in a single size category, 67.5 (84) 105 × 2.5 (3.5) 3.75 μm, devoid of conspicuous heads. The extremities may be pointed or blunt (Figs 11B, C). Microscleres: arcuate isochelae (Fig. 11D), 25 (25.6) 27.5 μm long; thin sigmas “C” (Fig. 11E) and “S” shaped, 32.5 (35) 37.5 × 1.25 μm.

Distribution and discussion.

In the original description Topsent (1936) distinguished in this species two size classes of acanthostyles similar in shape: the larger were 185-265 μm in length and the smaller 75-115 μm. Subtylotes straight or sometimes slightly sinuous, 225-275 × 3.5-4.5 μm, arcuate isochelae 23-25 μm long and sigmas 40-50 μm long and less than 1 μm thick. The specimens here described match with Topsent’s description apart from the presence of a single size class of acanthostyles. However, other authors ( Sarà and Siribelli 1962), recorded a single class of acanthostyles as well. This is a Mediterranean endemic species (Ligurian Sea and Central Tyrrhenian Sea). It was found on Cladocora caespitosa , at 15-40 m depth ( Topsent 1936) and on coralligenous bottom, at 40-70 m depth ( Sarà and Siribelli 1962).