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AbstractThis paper focuses on the skeletal architecture and morphotraits of the Mediterranean horny sponge Sarcotragus spinosulus(Demospongiae, Keratosa, Dictyoceratida, Irciniidae). This special endoskeletal system consists of a dense, variably complex connective architecture, which extends throughout the entire sponge body and is embedded in an abundant jelly-like extracellular matrix (ECM). To investigate the topographic arrangement and micro-morphotraits of these connective structures in detail and by colour, also during morphogenetic processes, histology techniques using light microscopy are essential. New information is provided on the coordinated morphogenetic processes that characterize the growth and assembly of collagenic prototype structures in the matrix of fibrous skeletal elements and drive skeleton remodelling. Our results also highlight some novelties and some remarkable peculiarities of fibrous, filamentous and fibrillar components at the levels of both composition and structure. The morphofunctional significance of skeletal architecture is suggested in the background of the anatomical complexity of S. spinosulus.

AbstractThis paper focuses on a faunistic inventory and the biogeographic pattern of Sardinian Porifera in a scarcely investigated Italian sea belonging to the Eastern Algero-Provençal Basin. The composition and structure of sponge fauna were studied in two priority habitats in two Marine Protected Areas (MPAs) of the North-Western Sardinian Sea. Shallow-water surveys investigated Posidonia oceanicameadows at five sites in the Asinara Island MPA and three karstic submerged caves in the Capo Caccia–Isola Piana MPA. The annotated checklist shows notably high values of taxonomic richness, confirming that P. oceanicameadows and karstic caves are key habitats for Porifera assemblages. Indeed, the sponge taxa recorded (n = 77) with 59 cave-dwelling and 45 taxa in seagrass meadows represent over 10% of the total Mediterranean sponge fauna, despite the small areas investigated, restricted biotopes and low sampling effort. This suggests that species richness is underestimated in circum-Sardinia seas. Internationally protected species (n = 6), rare species (n = 5) and Mediterranean endemic species (n = 14) were recorded. Previously investigated Posidoniameadows and caves share comparable values of species richness and endemicity with the Sardinian biotopes. The geographic range of species indicates that the biogeographic affinity of the NW Sardinian Sea sponge fauna is dominated by Atlanto-Mediterranean species. The three caves harbour a notably homogeneous sponge community, as indicated by the ca. 50% of shared species and high similarity index (> 83%). By contrast, the composition varies markedly among the five Posidoniameadows, which share only five species and display similarity values ranging ca. 20–60%. Unexpectedly when comparing these contrasting biotopes, faunal similarity is relatively low (< 40% shared species); indeed, Posidoniameadows harbour a notable number of cave-dwelling species in intermatte shaded microhabitats.