Sycon Risso, 1826

Borojevic, Radovan & Klautau, Michelle, 2000, Calcareous sponges from New Caledonia, Zoosystema 22 (2), pp. 187-201 : 196-197

Genus Sycon Risso, 1826

TYPE SPECIES. — Sycon humboldtii Risso, 1826 by subsequent designation (Dendy & Row 1913).

DIAGNOSIS. — Sycettidae with radial tubes partially or fully coalescent; distal cones are decorated by tufts of diactines. The inhalant canals are generally welldefined between the radial tubes and are often closed at the distal end by a membrane that is perforated by an ostium; they are devoid of a skeleton. There is no continuous cortex covering the distal ends of the radial tubes. Atrial and tubar skeletons are composed of triactines and/or tetractines.

Sycon gelatinosum (Blainville, 1834) ( Fig. 7 )

Alcyoncellum gelatinosum Blainville, 1834 .

MATERIAL EXAMINED. — One specimen.

LOCALITIES. — Canal Woodin, 25- 30 m.

DESCRIPTION

Sponge arborescent (2.5 cm high), with the cormus formed by regular bifurcations of the larger syconoid tubes at their bases, into smaller distal ones. A single osculum is found at the apex of each tube, which is surrounded by a thick layer of triactines arranged in parallel with a wide unpaired angle, which supports a short fringe of trichoxea. The external surface is smooth and granular, due to the thick bundles of short diactines that decorate the distal ends of radial channels, forming a typical, regular hexagonal pattern on the sponge surface (photo in Lévi 1998: 78). The inhalant spaces between the bundles are closed by a thin membrane, which is never supported by spicules. The sponge wall contains very regular radial choanocyte chambers intercalated by inhalant channels of the same size. The choanoskeleton is articulate, with numerous triactines arranged in parallel, and the unpaired actine directed towards the distal cones. Their size increases distally, and the spicules participating in the skeleton of the distal cone are larger and thicker than those in the tubes. The atrial cavity is slightly enlarged in the suboscular region, where the sponge wall is thinner. The atrial skeleton is composed of tetractines with large apical actines, which are bent towards the osculum, and are occasionally long enough to reach those arising from the opposite side of the atrium ( Fig. 7 ).

Spicules

Triactines of the choanosomal tubes are sagittal, with paired actines measuring 68.6 / 9.8 µm; the unpaired one is of the same size in the proximal part of the tubes, but measures 122.5 / 9.9 µm in the distal cones. The actines in the basal system of the atrial tetractines measure 58.8 / 9.8 µm. The apical actine measures 150 / 9.9 µm. The diactines of the distal tufts are irregular in size and shape, with the two actines of similar size, or with the proximal actine thinner, and the distal one conical or club-shaped, or irregularly bent (80.4 / 9.8 µm to 176.4 / 9.8 µm).

REMARKS

Sycon gelatinosum has been frequently reported from the Indian Ocean and the tropical regions of the Pacific Ocean.

Figures

FIG. 7. — Sycon gelatinosum (Blainville, 1834). Transverse section. Scale bar: 80 µm.