Siphonodictyon densum ( Schmidt, 1870 )

Van, Rob W. M., 2017, Sponges of the Guyana Shelf, Zootaxa 1, pp. 1-225 : 48

Siphonodictyon densum ( Schmidt, 1870)

Figures 30 a–c

Siphonochalina densa Schmidt, 1870: 34 .

Material examined. RMNH Por. 9922, Suriname, ‘ Luymes O.C.P.S. II’ Guyana Shelf Expedition, station M97, 7.3083°N 54.1667°W, depth 130 m, bottom coarse sand, 16 April 1969 .

Examined for comparison. Slide of Schmidt labeled with the present species name, BMNH 1870.5.3.129.

Description. ( Fig. 30 a) The specimen is a small group of tubes, that has become damged and partially fragmented during the collection and preservation process. The base of the larger tube is about 1 cm in diameter, a smaller one is only 0.5 cm in diameter. The upper parts of the tubes ar missing, so the height is not known. The outer surface is smooth, the inner surface is ridged. It looks as if on the inside of the tube there are septa dividing the tubar lumen, at least in the retrieved basal parts. Color (in alcohol) white or pale yellow. Consistency fragile.

Skeleton. ( Fig. 30 b,b1) Densely spiculated ectosomal crust with barely any openings between the spicules. As Schmidt (1870: 34) described, the curved fat spicules are arranged with the concave and convex sides closely adhering to form a continuous flat sheath ( Fig. 30 b1). The ectosome is carried ( Fig. 30 b) by a system of rounded meshes of 300–400 µm in size formed by tracts of 6–8 spicules in cross section.

Spicules. Oxeote strongyles only.

Oxeote strongyles ( Figs 30 c), curved, fat, with bluntly rounded ends, 151– 168 –186 x 17 – 19.2 –21 µm.

Distribution and ecology. Guayana Shelf, Florida, on sand bottom, 130–216 m depth ( Guyana Shelf 130 m).

Remarks. Examination of a slide in the Natural History Museum, London, presumed to have been taken from the Harvard type MCZ PORa-6471, confirmed the likely conspecificity of the Guyana specimen. The extremely dense arrangement of the ectosomal spicules is a characteristic shared feature. This is the first record of the species since Schmidt’s original description. There is considerable similarity with Siphonodictyon viridescens ( Schmidt, 1880) reported recently from Bonaire (Van Soest et al. 2014), but this has longer spicules (225–245 µm).

Figures

FIGURE 30. Siphonodictyon densum (Schmidt, 1870), a, habitus of RMNH Por. 9922 (scale bar = 1 cm), b, light microscopic of image surface skeleton, b 1, detail of b, c, SEM image of oxeote strongyles.