In the present Collective Article information on 26 taxa belonging to 8 Phyla and extended from the western Mediterranean to the Levantine Sea are presented. The new records were found in 9 countries as follows: Spain: first record for the Mediterranean of the crab Cancer bellianus; Algeria: further records of the alien fish Lagocephalus sceleratus to the west Algerian waters; Italy: first report on the presence and establishment of the ctenophore Mnemiopsis leidyi in Lessina and Varano Lagoons (W. Adriatic) and of Penaeus aztecus in Corigliano Gulf (Italian Ionian). Moreover, the extension of the distribution range of the polychaete Branchiomma bairdi to W. Sicily as well as that of the crab Ocypode cursor and the bryozoan Catenicella paradoxa to E. Sicily are cited. Slovenia: the record of the rare saccoglossan gastropod Placida cremoniana from Piran (Gulf of Trieste) is the first for the Adriatic; Greece: the native sea slug Eubranchus farrani is the first from the Eastern Mediterranean; many sightings of the bamboo corals Isididae distributed along all the E. Ionian Sea and the establishment of P. aztecus in all Greek waters are also reported for first time; the westernmost extension of the alien urchin Diadema setosum in Cretan waters is cited and new sights of the alien species Goniobranchus annulatus and Pterois miles are shown. Turkey: the alien fish Champsodon capensis is reported for first time from the Aegean Sea and the native acari Agauopsis microrhyncha from the Levantine Sea; a new observation of the alien crab Atergatis roseus in Güllük Bay-Aegean is also mentioned; Cyprus: first records of the alien urchin D. setosum and Lobotes surinamensis in Cypriot waters; Lebanon: several sightings of Monachus monachus from the Lebanese waters indicate a potential better status of the species in the area, Egypt: first records of the alien crab Dorippe quadridens and the alien gastropods Nerita sanguinolenta and Conomurex persicus from the Mediterranean Egyptian waters; extension of the distribution range of Diodora funiculata and Diodora rueppellii and a second record of the alien Nerita sanguinolenta in the same area.

Fenestrulina malusii (Audouin & Savigny), the type species of Fenestrulina Jullien, is among the most widely reported bryozoans globally. Following the loss of the original type material, presumed Mediterranean in origin based on Savigny’s depiction on Sargassum, we designate a neotype from a colony on deep Laminaria blades off Ustica Island (Tyrrhenian Sea). Additionally, seven new species are described from various habitats across the Mediterranean: F. cavernicolasp. nov., from the semi-dark and dark zones of a submarine cave in Lesvos Island (NE Aegean Sea); F. communissp. nov., from beach-cast plastic near Palermo (NW Sicily); F. foveolatasp. nov., from Ile-Rousse Bank (Corsica); F. granulosasp. nov., from Posidonia meadows in Dhiaporia (Chios Island, Aegean Sea); F. kallistesp. nov., from outer-shelf coarse sediments off Calvi (NW Corsica); F. ovatasp. nov., from Trémies submarine cave, near Marseille (Gulf of Lion); and F. variorugosasp. nov., from Posidonia rootlets off Formica Isle (Egadi Archipelago, near the Sicily Strait). Five of these species are currently known only from their type localities, while F. communissp. nov. and F. variorugosasp. nov. occur elsewhere. An additional species with distinct features is described but left in open nomenclature owing to the absence of an ovicell. A comprehensive review of the published images of the 77 species currently assigned to Fenestrulina, with the identification of new diagnostic features, including kenozooids, has led to a revised diagnosis of the genus.

Although several bryozoans are considered habitat-former species, allowing colonisation by epibionts and promoting biodiversity, studies dealt so far with only some, usually constructional, species. In this context, the present study focuses on the epibiosis found on the erect mineralised but flexible species Margaretta cereoides, contributing with some macroalgae to the canopy formation on a coralligenous build-up collected at 36.7 m depth offshore Marzamemi (Ionian Sea, Mediterranean) in the frame of the project CRESCIBLUREEF. Focusing on bryozoans and serpulids we documented high diversity (species richness) on the investigated substrata (M. cereoides, Flabellia petiolata, Peyssonnelia rubra, Osmundaria volubilis and all other fleshy algae including Phyllophora crispa). Diversity, total number of colonies/specimens hosted, and number of colonies/specimens per cm² are higher on M. cereoides than on algae, possibly in relation with the morphology, robustness and persistence of the surface offered by the bryozoan contrasting with the flexible and ephemeral nature of most algae, often provided with chemical defenses. Bryozoan and even more serpulid epibiont diversity on M. cereoides is also higher than those reported for studied species in the Mediterranean and for Flustra foliacea from North Europe.