Silver nanoparticles (AgNPs) incorporation in commercial products is increasing due to their remarkable physical and chemical properties and their low cost on the market. Silver has been known for a long time to be highly toxic to bacterial communities, aquatic organisms, and particularly to marine biota. Strong chloro-complexes dominate Ag speciation in seawater and facilitate its persistence in dissolved form. It has a great impact on marine organisms because low concentration of silver can lead to strong bioaccumulation, partly because the neutral silver chloro complex (AgCl0) is highly bioavailable. Owing to the fact that estuaries and coastal areas are considered as the ultimate fate for AgNPs, the study of their toxic effects on marine invertebrates can reveal some environmental risks related to nanosilver exposure. In an attempt to reach this goal, many invertebrate taxa including mollusks, crustaceans, echinoderms and polychaetes have been used as biological models. The main findings related to AgNP toxicity and marine invertebrates are summarized hereafter. Some cellular mechanisms involving nano-internalization (cellular uptake, distribution and elimination), DNA damaging, antioxidant cellular defenses and protein expression are discussed. Physiological effects on early stage development, silver metabolic speciation, immune response, tissue damaging, anti-oxidant effects and nano-depuration are also described. Finally, we paid attention to some recent interesting findings using sea urchin developmental stages and their cells as models for nanotoxicity investigation. Cellular and physiological processes characterizing sea urchin development revealed new and multiple toxicity mechanisms of both soluble and nano forms of silver.