Pleraplysilla minchini Topsent, 1905 Fig. 13

Pleraplysilla minchini Topsent, 1905: 184.

Description.

Growth form encrusting (1-5 mm in thickness). Consistency soft. Colour light brown to light grey. Surface finely conulose. Exhalant canals evident on the sponge surface, converging in scattered oscules 1-2 mm in diameter. Flagellate chambers from oval to rounded (50-90 µm in diameter). Skeleton typically dendritic with fibres (1-3 mm in height ca. 160 µm in diameter at their base) rising from a basal plate. Fibres laminated, normally with a single apex supporting a conule but, in some cases, arborescent with 2-3 branches. Fibres evidently cored with irregularly dense foreign debris, mainly spicule fragments.

Habitat.

Cave, rocky bottom, artificial reefs. Bathymetric range 1-30 m.

Mediterranean caves.

Niolon Cave (Gulf of Lions); Monte Vico, Secca delle Formiche-Vivara, Mago caves (Central Tyrrhenian Sea) (Laborel and Vacelet 1958; Pulitzer-Finali and Pronzato 1976; Pansini et al. 1977; Pulitzer-Finali 1977; Pronzato and Manconi 2011).

Remarks.

As for diagnostic traits the genus Pleraplysilla is anomalous among the Dictyoceratida, for the trait 'dendritic not anastomosing skeleton’ . As for the taxonomic status Pleraplysilla minchini is regarded by Vacelet (1959) as a synonym of Pleraplysilla spinifera . Later authors, as Cabioch (1968) and Borojevic et al. (1968), considered both species as valid. The material available for our study seems to confirm a specific divergence between the two. Pleraplysilla spinifera is generally recognizable at sight by the very pronounced, spaced conules. Its fibres reach a length of 12 mm, with a thickness of 450 µm near the base; they are generally branched; sometimes more than one fibre starts from a common basal plate; the inclusions are mostly closely-packed sand grains. In Pleraplysilla minchini the fibres are less widely spaced, they reach not more than 3 mm in length and a diameter of 160 µm near the base; they are generally not branched and there is a prevalence of sponge spicules in their inclusions.