Pleraplysilla minchini Topsent, 1905

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 : 18-19

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.