Limacina

Limacina is a genus of swimming predatory sea snails commonly known as sea butterflies in the family Limacinidae. This genus contains some of the world's most abundant gastropod species. Etymological meaning of the generic name Limacina is 'snail-like'. As pelagic marine gastropods, Limacina swim by flapping their parapodia, inspiring the common name sea butterflies. Sea butterflies are part of the clade Thecosomata. Sea angels, similar to Limacina, are in the order Gymnosomata. Both of these orders are still referred to as 'pteropods'. Sea butterflies of the order Thecosomata have a shell, while sea angels in the order Gymnosomata do not. The shells of Limacina are well developed, sinistrally coiled, turret-like, and include an operculum. Shell size and thickness vary within the genus. At high latitudes, the diameter of the shell does not exceed 15 mm. At lower latitudes, the diameter varies from 1 to 3 mm. Two large winglike parapodia, derived from foot tissue, propel these invertebrates through the water column to overcome negative buoyancy due to the animal's shell. As diel vertical migrators, Limacina inhabit deeper waters during the day and travel to the surface at night to feed. Feeding habits of Limacina are characterized by actively feeding on planktonic organisms such as bacteria, small crustaceans, gastropod larvae, dinoflagellates and diatoms. These prey items become entangled in a mucosal web (up to 5 cm wide) excreted by the animal that is, in turn, eaten along with the prey items. This net also provides positive buoyancy. Ciliated posterior footlobes and lateral footlobes move food collected by the mucosal web into the mouth. Large aggregations of Limacina migrating to the surface of the water attract predators such as Clione (family Clionidae, suborder Gymnosomata), baleen whales, various species of salmonids, herring, and seabirds.