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Notodiaphana atlantica and Liloa mongii are two cephalaspidean species described respectively from the Atlantic Ocean and the Red Sea, and considered widespread in their native ranges. Both species have also been recently recorded from the Mediterranean Sea, prompting some authors to consider them alien. Notwithstanding clear morphological differences in their shells, the two species have often been confused or misidentified in the literature, or specimens have been described with incorrect locality data. We hereby review the occurrence, distribution and status of both species in the Mediterranean Sea based on published data and examination of new material. Notodiaphana atlantica is considered a cryptogenic species with a range spanning from the western to eastern part of the basin. The presence of L. mongii in the Mediterranean is questioned until specimens that can be reliably assigned to this taxon or to any congeneric species are found in the area. Alien species inventories play an important role in regional policy and management decisions, thus requiring a high degree of confidence in the validity of species identification and their non-indigenous status. The present paper adds further evidence of the excess of “bibliographically introduced” alien records and reiterates the need for periodic re-evaluation of published data.

The mollusc fauna of the Mediterranean Sea is still considered as the best-known marine mollusc fauna in the world. The previous modern checklists of marine Mollusca were produced by joint teams of amateurs and professionals. During the last years the Italian Society of Malacology (Società Italiana di Malacologia – S.I.M.) maintained an updated version of the Mediterranean checklist, that served as the backbone for the development of the new Italian checklist. According to the current version (updated on April 1st, 2021), 1,777 recognised species of marine molluscs are present in the Italian Economic Exclusive Zone, including also the Tyrrhenian coasts of Corsica and the continental shelf of the Maltese archipelago. The new checklist shows an increase of 17% of the species reported in the 1995 Checklist. This is largely (yet not solely) due to the new wave of studies based on Integrative Taxonomy approaches. A total of 135 species (7.6%) are strictly endemic to the Italian waters; 44 species (2.5%) are alien and correspond to the 28% of the Mediterranean alien marine molluscs. All eight extant molluscan classes are represented. The families represented in the Italian fauna are 307, an increase of 14.6% from the first checklist, partly due to new records and partly to new phylogenetic systematics. Compared with the whole Mediterranean malacofauna, the Italian component represents 71% in species and 61% in families, which makes it a very remarkable part of the Mediterranean fauna.

Fouling communities were studied in three port systems of Northern Tyrrhenian Sea (Western Mediterranean), focusing on the occurrence of non-indigenous species (NIS). For each port system two harbour types (large port and recreational marina) were sampled and, within each large port, fouling samples were collected considering two use destinations (commercial and touristic harbour). Among the 431 taxa identified, forty-two were alien or cryptogenic, four of which were new records for the study area. Harbour type and use destination shaped fouling communities and NIS assemblages, with their relative influence varying among different port systems. High fouling variability was detected within port environments and between different marinas. NIS showed the highest occurrence in large ports, in which the touristic harbour generally hosted the greatest amount. Therefore, the touristic harbours within large ports were identified as susceptible areas for NIS establishment and their possible subsequent spread at local scale through recreational maritime traffic.

The family Cerithiopsidae H. Adams and A. Adams, 1853 is distributed worldwide, and comprises around 800 extant species divided into ~40 genera. The most speciose genus within the family is Cerithiopsis Forbes and Hanley, 1850, a taxon currently used as a general receptacle rather than as a proper phylogenetic lineage. We hereby redescribe the rare species Cerithiopsis horrida di Monterosato, 1874, review its nomenclature, known material, and distribution as well as figure the entire protoconch, operculum, and radula for the first time. Our results highlight extreme differences between ‘Cerithiopsis’ horrida and the Cerithiopsis type species Cerithiopsis tubercularis (Montagu, 1803) and strong morphological and radular similarities with species belonging to the genus Retilaskeya Marshall, 1978. A wide discussion lists several taxa that might be ascribed to the same group of species, which presumably constitute a different worldwide lineage. Pending relevant molecular phylogenetic studies of the Triphoroidea Gray, 1847, for morphological conformity we suggest transferring ‘Cerithiopsis’ horrida to the genus Retilaskeya, and the same action is presumably appropriate for its possible sister species ‘Cerithiopsis’ leopardus Rolan and Gori, 2013. Finally, Retilaskeya better conforms to Newtoniellidae Korobkov, 1955 than Cerithiopsidae.

The taxonomic composition of the family Epitoniidae Berry, 1910 (1812) in Italian waters un-derwent relatively few changes in recent decades: except some nomenclatural changes andone reinstatement, only few species have been recently added to this fauna. Acirsa corsicana Nordsieck, 1974 is the last taxon described in the area and its status is currently disputed orwrongly assessed. After the examination of the holotype and comparisons with similar species,the status of A. corsicana is here properly assessed as junior synonym of Opalia coronata(Philippi & Scacchi, 1840). The specimen, until now kept in private collections, is depositedin an institutional repository (MNHNP).

According to the International Code of Zoological Nomenclature (ICZN, 2012: art 57.2), identical species-group names established for different nominal taxa, when originally combined with the same generic name, are primary homonyms. The junior name becomes therefore permanently invalid, except in few selected cases, which however are not met in the two species we will deal with below. The Principle of Priority requires that if a name in use for a taxon is found to be unavailable or invalid, it must be replaced by the next oldest available name from among its synonyms, including the names of the contained taxa of the same group (e.g., subgenera within genera), if that name is not itself invalid. If the rejected name has no potentially valid synonym a new substitute name must be established in its place (ICZN, 2012: art 23.3.5, art. 60). This is the case of two recently described extant molluscan taxa, whose specific names are preoccupied by homonymous fossil taxa.

Some shells of Ophieulima minima are reported from the Tuscan archipelago. This is the first record of the genus Ophieulima from the Mediterranean Sea. Hypotheses about its host are considered.