The concerns about the presence of microplastics (MPs) in marine ecosystems have widely increased in the past years. This is reflected in a growing number of studies addressing the effects of exposure to these materials in indigenous, farmed and even laboratory marine animals subjected to toxicity-oriented bioassays. There have been, however, many constraints in the detection of MPs in biological tissues, as routine histological techniques tend to degrade these materials, which are especially sensitive to organic solvents. This issue hinders the application of standard histopathological procedures based on convenient paraffin wax-embedding protocols, with consequences for biomonitoring and bioassay procedures. The method described here was developed and validated for the detection of polystyrene microplastics in biological tissue processed for paraffin-based histology. The strategy was developed and tested from whole-soft body sections of marine mussels that internalised the MPs following dedicated bioassays. The protocol is based on the replacement of xylenes with isopropanol for the purpose of intermediate infiltration and deparaffinization. Special modifications for staining, mounting and archiving are needed and are detailed as well. The protocol is shown to be a highly cost- and time-effective procedure compatible with formalin-based fixatives plus standard sectioning and staining, yielding complete preservation of MPs and optimal tissue conditioning. The method also produced excellent results with pre-stained MPs, with fluorochromes included, altogether providing excellent localisation of polystyrene MPs in paraffin-processed biological tissue.

Molluscs provided one of the pioneering approved pharmaceuticals from the seas: the painkiller ziconotide, developed from an ω-conotoxin isolated from cone snails. As marine biotechnologists are turning towards the immense range of novel bioproducts from marine invertebrates, little attention has been given to cephalotoxins, a group of obscure proteinaceous toxins produced by the salivary glands of coleoids, i.e., octopuses, squids and cuttlefishes. These toxins, for which there is empirical evidence for acting as immobilisers at least against crustaceans, are proteinaceous substances among the many that comprise the venomous mixtures secreted by these animals. Despite the ecological and economical importance of cephalopods, little is known about cephalotoxins, beginning with the actual span of taxa that secrete them. Indeed, cephalopods are long suspected for producing specific toxins as part of their predation and defence mechanisms, making them a promising group of marine animals for the bioprospecting of novel compounds. Despite scant or absent toxicological or otherwise experimental evidence for their bioreactivity, advances in “omics” methods have shed some light in the molecular structure of cephalotoxins. There are reports of cephalotoxins being complex glycoproteins that take part in a myriad of novel compounds being produced by the salivary glands. Still, there is no consensus of cephalotoxins being a conserved form of proteins. As Blue Biotechnology and marine bioprospecting for novel bioreactives are gaining momentum, the present review will provide the state-of-the-art on cephalotoxins, highlighting old and new research and existing gaps in the current knowledge.