Spongionella gracilis (Vosmaer, 1883)

Manconi, Renata, Cadeddu, Barbara, Ledda, Fabio & Pronzato, Roberto, 2013, An overview of the Mediterranean cave-dwelling horny sponges (Porifera, Demospongiae), ZooKeys 281, pp. 1-68 : 11

Spongionella gracilis (Vosmaer, 1883) Fig. 6

Velinea gracilis Vosmaer, 1883: 439.

Description.

Tubular habit with ten to fifteen slightly clavate hollow cylinders (up to 2 cm high, with a diameter of 5-8 mm) partly coalescing and arising from a common basal spongin plate (ca. 4.5 × 3 cm in diameter). Consistency soft and elastic, as the rule in all Spongionella species. Oscules apical (2-3 mm in diameter). Surface finely conulose with conules supported by tips of ascending fibres (conules ca. 100 µm high, 300 µm apart). Skeleton reticulate with a more or less regular network of generally quadrangular meshes (100-300 µm in diameter). Primary fibres (25-30 µm in diameter) connected by rare and irregular tracts (5-10 µm in diameter). Fibres laminated, clear, and uncored, with a transparent axis.

Habitat.

Cave, rocky bottom, epibiotic on Corallium rubrum . Bathymetric range 9-45 m.

Mediterranean Caves.

Secca delle Formiche–Vivara Cave (Central Tyrrhenian Sea) ( Pulitzer-Finali and Pronzato 1976, 1980; Pulitzer-Finali 1977; Pronzato and Manconi 2011).

Remarks.

The reticulate fibrous skeleton is atypical for Dendroceratida.