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Home › Sea Life › Marine › Spineless › Mollusks › Snails › Sea Butterfly

Interesting Facts about Sea Butterflies

[Thecosomata] [Phylum: Mollusca] [Class: Gastropoda] [Order: Pteropoda] [Family: Opisthobranchia]

Sea butterflies are a suborder of swimming marine snails that contain various specimens of slow-moving gastropod mollusks, including their close relatives the 'shell-less' sea angels.

The facts and information in this guide highlight the vital role of the sea butterfly in our marine ecosystems and for the oceanic food chain.

Sea Butterfly Habitat and Geographic Range

You will find ocean butterflies occupying almost all deep water pelagic zones around the world.

Thus, they thrive best away from the shorelines of most warm and cold seawater environments, with several hot spots being:

• British Columbia
• California
• The North Atlantic Ocean

So, why are they called the 'sea butterfly' and how do they fulfil their pivotal role in the food chain? Simply put, the name comes from the way they use parapodia (wing-like lobes) for movement through the water. So you could say the water butterfly mirrors the land butterfly.

They are also known as the 'potato chips of the sea'. In fact, thecosamata species are an important food source for the majority of Arctic marine species, especially fishes, zooplankton, and seabirds.

Note: Even though sea angels (clade Gymnosomata) are similar, there are notable differences in appearance. So for example, the butterfly of the sea has a calcium carbonate case. But the body of a sea angel is transparent and gelatinous - not a calcified shell.

Appearance, Diet, and Behaviour

Sea butterflies are Pteropod mollusks (free-swimming sea snails). They are a pelagic marine gastropod that also falls under the subclass of Opisthobranchia (phylum Mollusca).

One notable modification is a pair of winglike flaps (used in swimming). Despite being less than one centimetre in length (around 0.4 inches), they tend to live away from rocky coastlines. Instead, they will spend most of their life near the surface of open oceans.

What Do Sea Butterflies Eat?

The sea butterfly is mainly passive in its feeding habits - with 'trapped' plankton being its primary source of food.

These tiny marine snails create a mucous net (around 5 centimetres in size) to capture any tiny plankton that floats into the web.

They will follow large blooms of planktonic animals by migrating deeper into the water column.

Even though sea butterflies spend a lot of time in warm surface water during the darkness at night, they will visit the deeper waters of the arctic and tropical oceans at dawn as the sun starts to rise.

Types of Sea Butterfly (pteropods)

Sea Butterfly Reproduction and Threats

Ocean butterflies are hermaphroditic, meaning the young have male and female reproductive organs. But, even though they start their life as a male, they need to reach adulthood before they can start producing eggs. Their reproductive process ends with the release of fertilised eggs into the water to hatch.

Several large predators, such as whales and fish, consume copious amounts of sea butterflies. In fact, many large animals would struggle to survive without an abundance of these tiny organisms.

They also need to watch out for predatory seabirds, especially terns and Bonin petrels, when they swim close to the water's surface.

Marine Creatures Vulnerable to Ocean Acidification

Pteropods use mineral aragonite to form their shell. Thus, the effects of ocean acidification (changes to PH) can hinder the normal processes for building their protective armour.

Human activities cause significant changes to their natural habitat. As a result, acidic increases have now become the biggest threat to the existence of sea butterflies.

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