Sycettusa sibogae ( Burton, 1930 )

Van Soest, Rob W. M. & De Voogd, Nicole J., 2015, Calcareous sponges of Indonesia, Zootaxa 3951 (1), pp. 1-105 : 80-82

Sycettusa sibogae ( Burton, 1930)

Figures 58a–d , 59a–c

Grantessa sibogae Burton, 1930: 4 .

? Sycettusa sibogae ; Van Soest et al., 2011: 40, fig. 19.

Material examined. Holotype ZMA Por. 00148, Indonesia, Borneo Bank , E of Kalimantan, 3.45°S 117.6°E, depth 59 m, dredge, bottom fine grey sand, coll. Siboga Expedition stat. 077, 10 June 1899; BMNH 1929.8.30.2a, 2 slides from holotype, same data.

Description. A single thin-walled elongated tube ( Fig. 58a ), with terminal naked oscule (but examined microscopically, there is evidence of a very short fringe, Fig. 58c ), size 2 cm high, 0.5 cm diameter, whitish in alcohol, surface rough to the touch, consistency firm, brittle.

Histology. Syconoid arrangement (assumed on the basis of genus assignment).

Skeleton. Inarticulate ( Figs 58b, d ), with a thick cortex of giant triactines, supported by the unpaired and the smaller paired actines of subcortical pseudosagittal triactines. Trichoxeas are found in a very short oscular fringe ( Fig. 58c ) and are scattered in low abundance in the cortical region. The choanosomal skeleton is formed by the longer unpaired actines of the pseudosagittal spicules ( Figs 58b, d ). Atrial skeleton formed by multiple layers of smaller sagittal triactines ( Fig. 58d ).

Spicules. ( Figs 59a–c ) Giant triactines, pseudosagittal triactines, sagittal triactines, trichoxeas.

Giant triactines ( Fig. 59a ), equiangular, equiactinal, actines variable in size, 282– 475.5 –660 x 32– 36.8 –44 µm (Burton gives 400 x 36 µm).

Atrial sagittal triactines ( Fig. 59b ), equiangular, unpaired actines 100– 128.3 –165 x 7– 7.8 –10 µm, paired actines up to 50– 57.1 –66 x 6.5– 6.6 –7 µm.

Pseudosagittal triactines ( Fig. 59c ), variable in size, unpaired actines 66– 166.7 –240 x 14– 17.3 –22 µm, longer paired actines 129– 294.8 –486 x 12– 18.8 –22 µm, and shorter paired actines 51– 123.7 –220 x 12– 17.3 –19 µm.

Trichoxeas, straight, invariably broken, pieces varying between 50 and 500 x 1 µm (discovered only in the sections; probably because of their thinness these were not found in the SEM preparation).

Ecology. Sandy bottom at 59 m depth beyond the reefs.

Distribution. Indonesia;? Clipperton Island.

Remarks. Among the species of Sycettusa , the present species is unusual in possessing a cortical skeleton of giant triactines, with actines up to 600 µm. Burton (1963) synonymized this species with Mauritian Sycettusa sycilloide s ( Schuffner, 1877) (originally as Sycortis ), without further comment. There are large differences in spicule sizes with this species, e.g. the subectosomal pseudosagittal triactines have the longer actine twice as large as in S. sibogae , the triactines of the ectosomal cortex in contrast are much smaller than in S. sibogae . Together these differences are sufficient to keep the two species separate.

Van Soest et al. (2011) reported this species from Clipperton Island, East Pacific, depths 17–32 m, with hesitation (indicated as ‘ aff. ’ sibogae ). This specimen consisted of a cluster of yellow-brown tubes (in alcohol), which have similar spiculation as S. sibogae . The cluster of tubes, the color (in alcohol) and the geographic distance make conspecificity not very likely.

Genus Grantessa Lendenfeld, 1885

Figures

FIGURE 58. Sycettusa sibogae (Burton, 1930), holotype ZMA Por. 00148 from Kalimantan, a, habitus of preserved holotype (scale bar = 1 cm), b–d, BMNH 1929.8.30.2a slides of holotype, b, cross section showing inarticulate skeleton made up of the paired actines of pseudosagittal triactines on the outside covered by the paired actines of regular giant triactines, on the atrial side with a cover of atrial sagittal triactines (scale bar = 500 µm), c, tangential view of the skeleton of the oscule showing a short fringe of trichoxeas (scale bar = 200 µm), d, detail of the peripheral skeleton showing giant cortical triactines and subcortical pseudosagittal triactines (scale bar = 200 µm).

FIGURE 59. Sycettusa sibogae (Burton, 1930), holotype ZMA Por. 00148 from Kalimantan, SEM images of the spicules, a, giant and intermediate regular triactines, b, sagittal triactines, c, pseudosagittal triactines (diactines of the oscular fringe were not available for SEM study).