Sycettusa aff. sibogae ( Burton, 1930 ) Burton, 1930

Van, Rob W. M., Kaiser, Kirstie L. & Syoc, Robert Van, 2011, Sponges from Clipperton Island, East Pacific, Zootaxa 2839, pp. 1-46 : 40

Sycettusa aff. sibogae ( Burton, 1930) n.comb.

( Figs 19 A–H)

Grantessa sibogae Burton, 1930: 4 .

Material examined. MNHN DCL 4045–D, Jean-Louis Etienne Expédition Clipperton 2005, station 13, 32 m, on dead corals, 18–01–2005, 2 specimens.

MNHN DCL 4057, Jean-Louis Etienne Expédition Clipperton 2005, station 5, 17 m, on dead corals, 10–01– 2005, 1 specimen. ( Fig. 19 A).

MNHN DCL 4064, Jean-Louis Etienne Expédition Clipperton 2005, station 40, 20 m, on dead corals, 29–01– 2005, 1 specimen.

Examined for comparison: Holotype, ZMA Por. 0 0 148, Siboga Exped. stat. 0 77, Indonesia, Borneo Bank, Makassar Strait, 3.45°S 117.6°E, depth 59 m, 10–06–1899.

Description. A clustered mass of tubes ( Fig. 19 A), the largest 5 x5x 2 cm, individual tubes up to 1 cm long and 0.5 cm in diameter. Color (alcohol) pale yellow-brown.

Skeleton. Compressed syconoid without articulation ( Fig. 19 B). The thin cortex is made up of the actines of cortical equiangular triactines, the choanosome is made up of the unpaired actines of the subcortical larger sagittal triactines; atrial skeleton likewise made up of the paired actines of smaller equiangular triactines.

Spicules. Triactines only ( Fig. 19 C). These are quite diversified, basically divisible in (1) equiangular triactines, large ( Fig. 19 D), with actines up to 530 x 47 µm, and small ( Fig. 19 E) up to 164 x 19 µm, and (2) unequiangular triactines which often have downcurved or upcurved paired actines, consisting of large triactines ( Fig. 19 F) with paired actines up to 290 x 38 and unpaired actine up to 525 x 45 µm, and small triactines ( Fig. 19 G) with paired actines up to 47 x 7 and unpaired actine 90 x 9 µm. There are also atrial intercrossing trichoxeas ( Fig. 19 H), invariably broken, largest unbroken fragment: 240 x 1.5 µm.

Ecology and distribution. Encrusting dead corals in shallow reefs; if conspecific with the Indonesian material the species is known from Île Clipperton and the Makassar Strait region.

Remarks. The genus Sycettusa unites former Grantessa species lacking an articulated skeleton ( Borojevic et al. 2002). The species Grantessa sibogae Burton (1930) was synonymised with the apparently widespread Indo- Pacific species Sycettusa sycilloides ( Schuffner, 1877 as Sycortis ) by Burton (1963) without further comments. For that reason and because Schuffner’s material was from East Africa ( Mauritius) we prefer to retain Sycettusa sibogae n.comb. as a distinct species. The type of S. sibogae n.comb. (ZMA Por. 00148) from Makassar Strait, Indonesia, is a single tube and the large triactines have their rays somewhat more curved than in our material but spicule sizes and categories match to a large extent. The possibility that the Clipperton specimens belong to a closely related but distinct species cannot be entirely excluded. For that reason we added ‘ aff .’ to the species identification.

Sycettusa tenuis Borojevic & Klautau (2000) from New Caledonia differs from the present material in possessing atrial tetractines and lacking the subdivision in larger and smaller triactines.

Figures

FIGURE 19. Sycettusa aff. sibogae (Burton, 1930), A. habit of specimen MNHN DCL 4057, B. light microscopic view of peripheral skeleton, scale bar = 100 µm, C. overview of spicule complement, D. large equiangular triactine, E. small equiangular triactine, F. large unequiangular triactine, G. various sizes of unequiangular triactine, H. fragment of trichoxea.