Understanding the impacts of microplastics on living organisms in aquatic habitats is one of the hottest research topics worldwide. Despite increased attention, investigating microplastics in underwater environments remains a problematic task, due to the ubiquitous occurrence of microplastic, its multiple modes of interactions with the biota, and to the diversity of the synthetic organic polymers composing microplastics in the field. Several studies on microplastics focused on marine invertebrates, but to date, the benthic sea slugs (Mollusca, Gastropoda, Heterobranchia) were not yet investigated. Sea slugs are known to live on the organisms on which they feed on or to snack while gliding over the sea floor, but also as users of exogenous molecules or materials not only for nutrition. Therefore, they may represent a potential biological model to explore new modes of transformation and/or management of plastic, so far considered to be a non-biodegradable polymer. In this study we analysed the stomachal content ofBursatella leachii,an aplysiid heterobranch living in the Mar Piccolo, a highly polluted coastal basin near Taranto, in the northern part of the Ionian Sea. Microplastics were found in the stomachs of all the six sampled specimens, and SEM/EDX analyses were carried out to characterize the plastic debris. The SEM images and EDX spectra gathered here should be regarded as a baseline reference database for future investigations on marine Heterobranchia and their interactions with microplastics.

Microplastic pollution constitutes a serious environmental problem that requires more effective scientific research to describe its potential impacts on marine fauna. The interaction between microplastics and marine biota can have significant negative effects through the trophic chain, up to human health. To date, several steps forward have been made in our understanding of this phenomenon; however, large knowledge gaps still exist for several taxa and areas. In particular, the pattern of spatial and temporal distribution of microplastics in marine sediments and their interaction with benthic detritivore species still needs to be addressed. The Mediterranean Sea is one of the most impacted areas of the world, and its biota is deeply affected by microplastic pollution. To investigate the effects of the presence of microplastics in the sediments in this area, the echinoderm Holothuria tubulosa was chosen as a model species, and specimens were collected along the Salento peninsula in Apulia, Southern Italy. This peculiar geographic area extends between two ecoregions of the Mediterranean Sea, the Northern Ionian and the Southern Adriatic seas, characterized by peculiar and distinct currents and submarine topologies, resulting in a complex and dynamic ecosystem affected by seasonal fluctuations that make the Salento peninsula an interesting natural laboratory for predictions of future dispersion events on a wider scale. Microplastics were analyzed by investigating the gut contents of H. tubulosa individuals, and the SEM/EDX method was used to confirm the plastic material extracted. Results revealed microplastics in all the specimens analyzed and with a homogeneous pattern of distribution in time and some differences in space, suggesting that the presence of this anthropogenic material is constant throughout the year and its quantity is only slightly affected by the level of conservation and management strategies characterizing the sampling sites.

Nudibranchs have a mostly carnivorous diet, and they prey on a wide variety of other animal taxa. Many species, mainly belonging to the Cladobranchia suborder, feed on cnidarians, including member of the class Hydrozoa. Several hydrozoan species display a symbiotic lifestyle, being associated with other benthic invertebrates, including for instance bryozoans, corals, octocorals, and sponges. In our knowledge, no record of nudibranch predation on symbiotic hydrozoans has been reported so far, possibly thanks to the protective action by the host towards its symbiotic hydrozoan. Here, we show the unexpected case of a nudibranch belonging to the recently described species Sakuraeolis marhe (Fernández-Simón and Moles, 2023) feeding on Zanclea sp. 2, a hydrozoan associated with the cheilostome bryozoan Celleporaria sp. This trophic association is confirmed by the presence and storage of the nematocysts into the nudibranch cnidosacs. Moreover, the nudibranch appears to selectively store mostly a single type of nematocyst, that is large size stenotele. The observation here reported represents the first well-documented record of a nudibranch feeding on a symbiotic hydrozoan and the first confirmed case of predation on Zanclea polyps. Moreover, we provide additional genetic information and the first description of the internal anatomy of S. marhe.

The “solar-powered” Elysia timida (Risso, 1818) is an endemic Mediterranean sacoglossan living in rocky substrates at shallow water. During a scuba dive, one E. timida was photographed and collected. The observation revealed the presence of a small crustacean of the Pinnotheridae family. It was not possible to assign the crustacean to a genus, but it shares typical ecological and external morphological features with other Pinnotherinae species. This is the first report of a pea crab hosted by a non-shelled Heterobranchia and the first case of a symbiotic association between crustaceans and marine Heterobranchia reported in the Mediterranean Sea.

The Mediterranean Sea is recognized as a hot spot of biodiversity, but the ever-increasing commercial and recreational marine traffic and global warming pose significant threats to its fauna by enabling and facilitating, respectively, the introduction of non-indigenous species (NIS). To mitigate negative effects in the native communities, greater efforts are being made to generate updated lists of NIS and to monitor their spread over space and time. In this regard, Amathia verticillata (delle Chiaje, 1822), a worldwide distributed arborescent bryozoan, can play an important role as a vector of NIS due to its ability to be a species ‘carrier of other species’. Despite its importance, a detailed study on the highly specialized Nudibranchia molluscs associated with A. verticillata is still lacking. Given that some nudibranchs serve as powerful bioindicators of changes in the Mediterranean Sea, and considering that A. verticillata is an invasive species capable to facilitating the establishment and spread of NIS, a broad bibliographic study coupled with field investigations in different anthropized areas of the Central Mediterranean Sea were conducted. The nudibranch fauna associated with A. verticillata in the Mediterranean Sea was assessed for the first time. Nine species were found associated with this bryozoan, five of which were directly observed and analysed using morphological and molecular techniques. A case of cryptic diversity was revealed, with Polycerella recondita Schmekel, 1965 resurrected as a valid species, and the neglected Tenellia granosa (Schmekel, 1966) reported for the fourth time in the Mediterranean Sea. Notably, only three out of the nine species are Indo-Pacific, while the remaining six taxa have an Atlantic/Mediterranean distribution. This finding prompted further phylogenetic and haplotype network analyses on the two nudibranch species directly associated with A. verticillata : Bermudella polycerelloides and P. recondita . These analyses revealed different and previously unknown ecological traits of the spread of these two species.

The Mediterranean Sea is considered a hotspot of molluscan diversity even if many marine environments are still poorly explored and could mask rare and/or neglected diversity. During a night survey in a rocky tide pool in the Adriatic Sea, near Ancona, Italy, Caliphylla mediterranea A. Costa, 1867, a rare sacog‑ lossan mollusc, was observed and documented. This finding constitutes the first record of this species for the Adriatic Sea and one of the few for the whole Mediterranean basin extending the known distributional range of this poorly known species.