A first record of the genus Aciculites in the Mediterranean Sea and the description of Aciculites mediterranea sp. nov. are here presented from a faunistic survey in a dark shallow marine cave of the north-western Sardinian karstic area. The new species is characterized by a massive cerebellum-like growth form, and a peculiar distribution of inhalant and exhalant areas, respectively, in depressed and elevated portions of the sponge surface. Oscules show a long narrow atrial cavity. Ectosomal skeleton is made of tangential anisostrongyles on elevated areas, and more or less vertical tufts of anisostrongyles in depressed inhalant areas. Anisostrongyles are smooth or with tips ornated by irregular tubercles. Sigmaspire microscleres are lacking. Choanosomal skeleton with tubercled irregular rizhoclone desmas and few scattered and variably oriented anisostrongyles. A comparative analysis of Aciculites mediterranea sp. nov. versus morphological diagnostic traits, geographical range and habitat of the species hitherto ascribed to Aciculites confirms that the peculiar distribution of the genus supports its relic condition of an ancient Tethyan fauna in the Mediterranean Sea.

Background The marine sponge Crambe crambe was chosen as an experimental model of sustainable shallow-water mariculture in the Sardinian Sea (Western Mediterranean) to provide biomass with high potential in applied research. Methods Explants were cultured in four long-term experiments (19 and 31 months at ca. 2.5 m depth), to determine the suitability of new culture techniques by testing substrata and seeding time (season), and monitoring survival and growth. Explants were excised and grown in an experimental plant close to the wild donor sponge population. Percentage growth rate (GR%) was measured in terms of surface cover area, and explant survival was monitored in situ by means of a digital photo camera. Results Explant survival was high throughout the trial, ranging from 78.57% to 92.85% on travertine tiles and from 50% to 71.42% on oyster shells. A few instances of sponge regression were observed. Explant cover area correlated positively with season on two substrata, i.e., tiles and shells. The surface cover area and GR% of explants were measured in the starting phase and monitored up to the end of the trial. High GR% values were observed both on tiles (>21%) and on oyster shells (>15%). Discussion The data on the behaviour and life-style of cultured fragments, together with an increase >2,400% in cover area, demonstrate that in situ aquaculture is a viable and sustainable method for the shallow-water biomass supply of Crambe crambe.

The discovery of conspicuous populations of the rare species Petrobiona massiliana is reported from shallow water karstic caves of Sardinia. The morphological comparative analysis versus previous data from the entire geographic range highlights that spicular traits seem to be highly conservative in contrast with a notable plasticity of growth form. Lifestyle and adaptive strategies that favoured the successful spread of P. massiliana in karstic caves and its persistence as extremely isolated populations in a fragmented habitat are discussed together with potential environmental constraints. The data indicate that conservation of this Mediterranean palaeoendemic species with a spot‐like distribution may be a challenge for the western Mediterranean Marine Protected Areas to confer protection to numerous co‐occurring cave‐dwelling species.