OpisthobranchiaOpisthobranchia

Opisthobranchs are soft-bodied marine gastropods lacking a visible external shell or operculum. Most possess two pairs of head tentacles: anterior chemosensory rhinophores, often intricately formed, and a posterior oral pair. Simple pit-cup eyes detect light and shadows. Many species feature exposed gills or dorsal appendages (cerata) for respiration and defence, while others have smooth, slug-like bodies. They range in size from a few millimetres to over 30 cm and display colours from cryptic camouflage to vivid patterns; the group name refers to the posterior position of their gills.

Opisthobranchs move slowly across surfaces using a broad foot, though some pelagic species can swim using wing-like parapodia. They are common residents of 🌊 Red Sea coral reefs, rubble areas, and seagrass beds, found from the intertidal zone down to depths exceeding 40 metres. Their diet includes sponges, hydroids, bryozoans, and algae. Many species sequester toxins or nematocysts from their prey, repurposing them for their own defence. They are hermaphroditic, engage in reciprocal sperm transfer, and lay their eggs in distinctive jelly-like ribbons. These often brightly coloured and slow-moving animals are frequently encountered by divers.