Overview
The Lion Nudibranch (Melibe viridis), also affectionately known as the ghost nudibranch or cast-net sea slug, is one of the most surreal and captivating marine gastropods in the Indo-Pacific oceans. Breaking dramatically from the classic nudibranch anatomy, this gelatinous, semi-translucent creature possesses neither radula nor rasping teeth; instead, it has evolved a colossal, radial oral hood lined with sensitive sensory tentacles that it casts out like a fisherman’s throwing net to ensnare live crustaceans.
Biology and Physical Characteristics
Melibe viridis exhibits an otherworldly appearance characterized by a translucent, yellowish-green to ghostly cream body studded with dendritic papillae and large, paddle-shaped dorsal appendages called cerata. When threatened, it can voluntarily shed these cerata (autotomy) to distract predators while secreting an unpleasant, sweet-smelling terpenoid chemical repellant. Its most breathtaking anatomical feature is the vast, circular cephalic hood, which can expand into an enormous translucent bowl fringed with dual rows of tactile sensory cirri.
Behavior and Ecology
Foraging primarily along sandy substrates and seagrass beds, the lion nudibranch sweeps its expanded hood back and forth across sediment like a vacuum hood. When small swimming amphipods or bottom-dwelling crabs contact the sensitive inner tentacles, the hood rapidly snaps shut like a drawstring pouch, trapping the prey in an internal water chamber before forcing it down its digestive tract. If dislodged from the seabed, Melibe viridis can swim gracefully through open water by laterally undulating its flattened body.
Conservation and Human Impact
Although not formally assessed by the IUCN Red List, Melibe viridis is widely distributed and locally common across healthy tropical seagrass and reef environments. As an unharvested marine invertebrate, its chief vulnerabilities include coastal habitat degradation, sedimentation from dredging, and seagrass bed destruction. It has also successfully colonized portions of the eastern Mediterranean via the Suez Canal as a Lessepsian migrant.
Interesting Factoid
The Lion Nudibranch hunts without teeth or claws—it expands its face into a giant translucent net up to 6 inches wide and slams it shut like a drawstring trap whenever an unsuspecting shrimp touches it!
Last updated: October 2026