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.

A new record of lithistid demosponges is reported from a western Sardinian karstic cave. Th e new specimen matches the trait of the genus Neophrissospongia (Corallistidae) for an ectosomal skeleton of radial dichotriaenes, a choanosomal skeleton as a network of dicranoclone desmas, and streptaster/amphiaster microscleres with short spiny rays bearing blunt tips. Th e cave-dwelling N. nana nov. sp. diverges from the other species of the genus in diagnostic characters such as the large irregular plate-like growth form, the topographic distribution of inhalant and exhalant apertures, and a smaller size of all spicular types. Moreover it displays an additional rare second type of dichotriaenes with smooth cladomes, shared with other genera of Corallistidae but never reported before for the genus Neophrissospongia. In addition N. nana nov. sp. bears stylelike sub-ectosomal spicules shared with N. microstylifer from deep water of New Caledonia. As for the latter trait, a present in-depth analysis of N. nolitangere from the Atlantic Ocean contrasts with previous historical records reporting monaxial spicules as oxeas/anisoxeas. Th e diagnosis of the genus Neophrissospongia is therefore emended for the growth form and for the micro-traits of dichotriaenes and monaxial sub-ectosomal spicules. Morphological data indicate that the new species is allied to N. nolitangere and N. microstylifer from Eastern Atlantic and New Caledonian deep water, respectively, and its record confi rms the highly disjunct geographic range of the genus Neophrissospongia in the Lusitanian-Macaronesian-Mediterranean area and the western Pacifi c Ocean supporting the relic condition of the genus in the Mediterranean Sea. Th is discovery stresses the key status of Mediterranean palaeoendemics as possible remnants of an ancient Tethyan fauna and focuses the need to plan conservation measures for these rare cave-dwelling sponges.

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.