Sea angel

All about the sea angel

A sea angel is a type of swimming snail. The muscular foot found in land snails evolved into parapodia, wing-like structures for swimming in open water. Sea angels have transparent, gelatinous bodies with no shells.

Sea angels vs. sea butterflies

Both sea angels and sea butterflies are pteropods—a specialized group of free-swimming sea slugs and snails. The main difference is that sea angels have no shell; their scientific name Gynmnosomata means “naked body.” Sea butterflies, or Thecosomata, are usually smaller and have shells.

Diet

Sea angels are predators that devour other swimming snails, including sea butterflies. One species, Clione limacina, is a very selective eater — it feeds exclusively on sea butterflies in the genus Limacina.

When the sea angel comes in contact with a prey item, it pushes out finger-like tentacles from its head that grab onto the prey. The sea angel then uses hook-like appendages to pull the prey out of its shell and into the sea angel’s gut. The whole process can take from two to 45 minutes.

Predators

Sea angels are an important food source for several animals including jellies, ctenophores, fishes, baleen whales, and birds. In the dimly lit waters of the deep sea, the sea angel’s transparent body helps it hide from predators.

Habitat

Sea angels are found worldwide in cold and temperate waters. They typically live in the midwater zone stretching from the surface down to 2,000 feet (600 m) deep. Remotely operated vehicles piloted by our research and technology partners at MBARI have observed sea angels as deep as 5,900 feet (1,800 m)!

How do sea angels reproduce?

Clione are hermaphroditic, meaning they have both female and male reproductive organs. During mating, sea angels come together for several hours at a time and fertilize each other. Once fertilized, a sea angel releases their eggs in a free-floating round mass.

Conservation

Ocean acidification and increasing ocean temperatures may leave sea angels with little to eat. They feed on sea butterflies whose shells are made from calcium carbonate. As the chemistry of the ocean changes, less calcite and aragonite are available to animals to build their shells and can result in smaller populations. 

Cool facts

• Sea angels have small wings compared to sea butterflies, but they are very strong swimmers. Sea angels are able to swim fast and maneuver quickly by moving their fins in a sculling motion. 
• A study found that salmon from the sea of Okhotsk get some of their red-pink color from pigments found in the gonads of sea angels. The sea angels get those pigments from the sea butterflies, which in turn get them from phytoplankton.