Almost everyone has tried to snorkel in order to discover what lives in the sea usually focusing on motile organisms (e.g. fish). However, there are many species attached to the substrate (sessile) that often go unnoticed. These organisms constitute the "benthos" and can form different types of gatherings, the so-called "benthic communities". Our project "Marine Creatures" is part of a bigger EU (H2020) project called Nautilos, which aims to develop a new generation of sensors and samplers for physical, chemical and biological essential ocean variables in addition to micro- and nano-plastics. Citizen Science (CS) and public awareness raising is a significant component of the Nautilos project. Crowd-sourcing activities for visual annotation of marine images are being performed by citizen scientists using underwater seabed images. Citizen scientists are detecting and classifying the most important groups of sessile fauna present, which all together form impressive marine communities commonly hidden from our eyes. The campaign and mass imagery crowd sourced data generation include selected taxonomic categories and major seafloor organism types, such as macroalgae, sponges, bryozoans and corals. Additional features such as macroplastics and litter are also being investigated. This voluntary Zooniverse project seeks the contribution of citizen scientists to identify the taxonomic groups of sessile benthic communities present in three different marine habitats: artificial reefs, marine ports and natural sea caves.