Rhabdastrella fibrosa Hechtel, 1983

Van, Rob W. M., 2017, Sponges of the Guyana Shelf, Zootaxa 1, pp. 1-225 : 77

Rhabdastrella fibrosa Hechtel, 1983

Figures 49 a–f

Rhabdastrella (Aurorella) fibrosa Hechtel, 1983: 81 , figs 23–24; Rhabdastrella fibrosa ; Muricy et al. 2011: 41, fig. 5F.

Material examined. RMNH Por. 9785, Guyana, ‘Luymes’ Guyana Shelf Expedition, station 51, 7.6833°N 57.0333°W, depth 98 m, bottom calcareous sand, 30 August 1970 .

Description. Lobate sponges ( Fig. 49 a) with smooth dark red-brown surface. A few small contracted oscules crown the upper surface of the lobes. Size of the two specimens respectively 4.5 x 3 x 2 cm and 4 x 2 x 1.5 cm. Interior lighter colored, Consistency crumbly, compressible.

Skeleton. A dense cortical region of 2 mm thickness consisting of packed strongylospherasters, pierced by oxeas and carried by the cladomes of subcortical ortho/plagiotriaenes. Choanosomal skeleton with low spicular density, many megascleres singly, with few bundles.

Spicules. ( Figs 49 b–f) Oxeas, ortho/plagiotriaenes, strongylospherasters, oxyasters.

Oxeas ( Figs 49 b,b1), elongately fusiform, with many thinner stages, 1130– 1275 – 1440 x 14– 29 –41 µm.

Ortho- to plagiotriaenes ( Figs 49 c,c1), in a large size range, but not readily divisible in size categories, with conical endings of cladi and rhabdomes, cladi usually angled almost in the same plane except for the central axial part which is curved inwards; cladi occasionally wobbly or curled; rhabdomes 576– 814 – 1110 x 24 – 41 –63 µm; cladomes 213– 386 –540 µm; cladi 121– 198 –270 x 19 – 32.5 –48 µm.

Strongylospherasters ( Figs 49 d–e) in two size categories, the larger ( Fig. 49 d) of which are anthasters, i.e. the rays and center are predominantly smooth and only the rounded tips are heavily spined, diameters 22– 27.4 –32 µm (number of rays difficult to determine but at least 20 or more); the smaller category ( Fig. 49 e) have the entire rays spined and smooth parts are confined to the small center, diameters 4– 6.7 –10 µm, ray number 6–10.

Oxyasters ( Fig. 49 f) with entirely spined, sharply pointed, conical rays, diameters 9– 11.6 –14 µm, ray number 6–8.

Distribution and ecology. Guyana Shelf, NE Brazil, sandy bottoms at 27–98 m depth (previously 27 m).

Remarks. The drawing of the habit in Hechtel (1983) differs rather strongly from our specimens, showing large oscules with pink oscular rims. This also applies to the photo of the specimen provided later by Muricy et al. 2011 (their fig. 5F). Nevertheless, the spiculation is closely similar to our specimens, leaving little doubt that our material is conspecific with Hechtel’s. A second species of Rhabdastrella , R. virgultosa Boury-Esnault, 1973 occurs in NE Brazil. It has no triaenes and the microscleres include large ‘sterrospherasters’, up to 50 µm in diameter, which necessitates redescription of the type in order to check the generic assignment. The genus Rhabdastrella is defined as having large spheroxyasters in a dense ectosomal layer, and it seems that both R. fibrosa and R. virgultosa do not conform exactly to the genus definition, and appear rather inbetween Stelletta and Geodia .

Figures

FIGURE 49. Rhabdastrella fibrosa Hechtel, 1983, a, habitus of RMNH Por. 9785 (scale bar = 1 cm), b – f, SEM images of spicules, b, oxea, b 1, detail of one of the apices of b, c, ortho- to plagiotriaenes, c 1, cladome of c, d, anthaster, e, small strongylospheraster, f, oxyaster,