Sycettusa tenuis, Borojevic & Klautau, 2000

Borojevic, Radovan & Klautau, Michelle, 2000, Calcareous sponges from New Caledonia, Zoosystema 22 (2), pp. 187-201 : 197-198

Sycettusa tenuis n. sp.

( Fig. 8 )

TYPE MATERIAL. — Holotype MNHN-LBIM-C- 1999-03.

ETYMOLOGY. — From Latin tenu: thin, fragile.

MATERIAL EXAMINED. — One specimen.

TYPE LOCALITY. — South Lagoon, stn 274.

LOCALITY. — South Lagoon, between Vatia and Kauré, 2.6 miles from the Great Reef, stn 274, 44 m.

DESCRIPTION

Sycettusa tenuis is typical of the genus, with a thin and regular inarticulate skeleton. The cormus is composed of separated tubes that reach up to 3 mm in diameter. A thin wall of only 0.3 mm surrounds a wide central atrial cavity. The external surface is smooth. The skeleton ( Fig. 8 ) is composed of a thin cortex containing only triactines, scattered irregularly in a single layer. The choanoskeleton is supported by the inward actine of the subcortical pseudosagittal triactines, and the unpaired actine of the subatrial sagittal triactines. The thin atrial skeleton is composed of triactines, which occasionally develop a fourth short apical actine, and the atrial surface is thus decorated with very short spines (apical actines), which can be easily overlooked. All the spicules are approximately of the same size, but can be distinguished by their characteristic form.

Spicules ( Fig. 8 )

Cortical triactines with the unpaired actine straight, and the paired actines slightly curved, conical and ending with a sharp point, measuring 220 (± 25) / 18 (± 2) µm. Subcortical triactines are typically pseudosagittal, with the paired actines of similar size and shape, and the unpaired one sharply bent at the point that reaches the cortex, measuring 230 (± 20) / 20 (± 2) µm. The subatrial triactines have a wide unpaired angle. The short paired actines, measure 210 (± 20) / 20 (± 2) µm, while the longer unpaired one, measures 380 (± 50) / 20 (± 2) µm. In the atrial triactines and tetractines with long straight actines, the paired ones are only slightly curved at the distal part and measure 299 (± 50) / 20 (± 1) µm, while the unpaired one measures 350 (± 40) / 20 (± 1) µm.

REMARKS

Sycettusa tenuis n. sp. is certainly close to Sycettusa simplex (Jenkin, 1908) , which has a similar skeletal structure and spicules. The only distinction is the presence of atrial tetractines in S. tenuis . Sycetta stauridia Haeckel, 1872 is also apparently similar, but we distinguish it following Haeckel’s observation that the subatrial spicules are twice as thick as the subcortical ones. These species can be easily distinguished from S. poculum (Poléjaeff, 1883) , S. hastifera (Row, 1909) , S. glabra (Row, 1909) and S. sycilloides (Schuffner, 1877) , which all have radial diactines.

Figures

FIG. 8. — Sycettusa tenuis n. sp. Transverse section. Note the pseudosagittal subcortical triactines (arrow head) and the rare atrial tetractines with a short apical actine (arrow). Scale bar: 30 µm.