Range: Oceans worldwide Habitat: Open ocean Size: Less than 1 inch - 3 inches (2.54-7.62cm) long Diet: Plankton, marine snow, snails, and more

Threats: Fish and more Life span: One year or less

Transcript:

Today on animal fact files we’re talking about sea angels and butterflies. Originally these two groups were classified together in an order called “Pteropoda” but things have changed. Sea angels and sea butterflies are now each classified in their own orders. Because these animals do look rather similar on the surface, we’ll be discussing both groups in this episode, but maybe by the end you’ll have picked up on some of the differences between sea angels and sea butterflies.

These molluscs are often referred to as sea slugs, though perhaps that gives a wrong impression. For starters, there are already animals commonly known as sea slugs, the nudibranchs, who aren’t classified with these animals; but, hey, they still kind of look like slugs, right? Well, maybe the sea angels do, since they are completely lacking in a shell, but sea butterflies may more appropriately called “snails” because these animals do have shells!

Sea butterflies and sea angels are both protandrous hermaphrodites meaning they have both male and female reproductive organs at some points in their lives, but they start out with the male sexual organs developing first. Even though these animals have both sets of gametes, they still require a partner to produce offspring. While mating, they’ll cling to one another for upwards of four hours. During this time they may even hunt for food!

Now the kinds of food these animals seek is dependent on the type of animal. Sea butterflies collect food in the form of plankton and marine snow on tiny hair-like structures that can appear just about anywhere on their bodies depending on the species. These hair-like structures, called cilia, may be on the sea butterfly’s mantle or even inside the shell!

Sea angels, on the other hand, are more active predators. They will hunt their food and can swim and beat their “wings” much faster than sea butterflies. The “wings” of both sea angels and sea butterflies are modified feet. The “foot” of a mollusk is the structure they use to get around; so while terrestrial mollusks use it for creeping, sea angels and sea butterflies use their feet for swimming!

These animals are pelagic, meaning they live in the open ocean and they may be found from the surface of the water to more than 500 feet (150m) deep! And because these two groups occupy the same waters, they definitely come in contact with one another - this leads us to the diet of sea angels which is none other than sea butterflies.

The shells of sea butterflies even pile up at depths of more than 2,400 feet (730m) where they form what’s called a ‘pteropod ooze’. In size these animals don’t usually reach more than three inches in length, and many are much smaller. In tropical waters, where they’re most abundant, sea angels and sea butterflies may be less than an inch (2.54cm) long, but in temperate and even polar regions they reach more than three inches (7.62cm). It may also be that those living in colder regions live longer, however, on average they probably don’t even live up to a year.

Large groups of sea butterflies and sea angels may draw the attention of larger animals like herring and salmon or even baleen whales! In fact, when herring eat numerous amounts of sea butterflies, their internal organs will become stained and the fish will develop what’s known in the fishing world as “black gut.”

Now, when these animals eventually part ways from their partners, after having all kinds of other adventures in the process, they’ll release their eggs. Typically these are released in mucus batches, but some species actually brood their eggs. The eggs will remain in a brood pouch but the young eventually take over the parent’s body. When they get big enough, the babies will be released as the parent’s body disintegrates. As the larvae of sea angels develop, they’ll forgo their shells, but sea butterflies will retain theirs throughout their short lives.

For more facts on sea angels and butterflies, check out the links in the description. Thank you to Jenny for today’s request. Give a thumbs up if you learned something new today, and thank you for watching Animal Fact Files.