Tretodictyum reiswigi, Boury-Esnault, Nicole, Vacelet, Jean, Dubois, Maude, Goujard, Adrien, Fourt, Maïa, Pérez, Thierry & Chevaldonné, Pierre, 2017

Boury-Esnault, Nicole, Vacelet, Jean, Dubois, Maude, Goujard, Adrien, Fourt, Maïa, Pérez, Thierry & Chevaldonné, Pierre, 2017, New hexactinellid sponges from deep Mediterranean canyons, Zootaxa 4236 (1), pp. 118-134 : 126-127

Tretodictyum reiswigi n. sp. Boury-Esnault, Vacelet & Chevaldonné

Type-specimen. Sample VAL2-ACH-P15-ECH02. MNHN-HJV-04,

Type-locality. Valinco Canyon (Western Mediterranean) 41.662N / 8.795E, 397 m, 31/07/2014 .

Other material (available in SME collection): Sample CS-ACH-P03- ECH 06 b, a small fragment encrusting a brachiopod shell, Cassidaigne canyon (W Mediterranean) 43.047N / 5.397E, 370 m, 28/10/2009 . Sample VAL- ACH-P12- ECH 01 , small fragments, Valinco Canyon , Corsica, 41.663N / 8.795E, 444 m, 24/08/2010 . Sample from CYLYCE cruise, dive 12 of Cyana submersible, fragments of two tubes, Ile Rousse Canyon, NW Corsica, 42.833N / 8.953E, 320 m, 25/05/1997, Slides from specimens of BALGIM Cruise, R / V Cryos, Alboran Sea, Station CP 135-168, 35.435N / -4.301W and DR152–257, 35.935N/-5.569W, 390–560m, May–June 1984.

External morphology. The sponge is formed by several tubes more or less coalescent, expanding from a narrower base of attachment to the substrate. The tubes are most often arranged in a single or a double line ( Fig. 3 ), with each line formed by up to 12 tubes. The maximum size estimated from ROV images is ca 15 x 7 x 5 cm, with tubes either entirely joined or free for up to 5 cm. The tubes are 1–2.2 cm in diameter with a central canal 0.55–0.65 cm in diameter. The wall of the tubes is ca 3 mm thick. The surface is pierced by numerous small depressions. The color is pure white in living or freshly dead specimens, grey in dead skeletons due to sediment deposits. Specimens with both living parts and dead skeletons have often been observed ( Fig. 3 B). The consistency is hard, but the sponge is easily broken.

Numerous observations of sponges with very similar external characters have been made between 199 and 632 m depth from submersible and ROV dives, for examples Fig. 3 A, 3B; Fig. 4 B, 4C, 4D ( Table 3). Their identification to the same species is made with great confidence.

Skeleton. The main skeleton is a dictyonal framework of square meshes with 200–300 µm sides and beams 30–60 µm thick, with tubercles arranged in rows. Megascleres are dermal and parenchymal hexactins.

Strongyloscopules are present in dermal and atrial surfaces. Microscleres are oxyhexactins and two types of hexasters.

Figures

FIGURE 3. Tretodictyum reiswigi n. sp. A: Live specimen in Valinco Canyon, Corsica, 592 m. B: Mostly dead specimen with a single living tube (upper right), Cargese Canyon, Corsica, 536 m. C: Holotype, collected in Valinco Canyon, Corsica, 397 m. D, E: dictyonal framework. F: uncinate. G, H: hexactins with equal rays. I: hexactin with one longer ray. J: tylohexaster. K: oxyhexasters. L: strongyloscopule. A, B, C: Photos courtesy of AAMP.

FIGURE 4. Farrea bowerbanki n. sp. and Tretodictyum reiswigi n. sp. at the Cassidaigne canyon (Provence, NW Mediterranean), in areas exposed to industrial red mud discharge for decades. A: The highest density of F. bowerbanki observed so far, growing on (sub-fossil?) shells of the bivalve Neopycnodonte zibrowii, 580 m. In the center, the cold-water scleractinian coral Madrepora oculata. B: An isolated specimen of F. bowerbanki, ca 30 cm in diameter, and small specimens of T. reiswigi, at 536 m. C: High density of live T. reiswigi with a dead skeleton in the center, ca 480 m. D: Live specimens of T. reiswigi and F. bowerbanki at 521 m. The one on the lower left is apparently partly dead, as the distal parts accumulate red mud. A, B, D: Photos courtesy of COMEX S. A. C: Photo courtesy of MARUM - Center for Marine Environmental Sciences, University of Bremen, Germany.