Behind the Cinderella’s glass slipper

You thought you know everything about Cinderella story ?  Let’s check if you know this kind of jelly shoe !

Sea-butterflies belong to the snails family, but they are planktonic organisms. Their scientific name is Thecosomata which is a taxonomic suborder of small pelagic swimming sea gastropods. This term refers to organizations whose body is contained in a cartilaginous shell.

As all planktonic organism, Thecosomata are carried along with the currents. This way of life had led to a number of adaptations in their bodies.

> Sedimentation rate must be very low to prevent these animals sink (they can not really swim). As a result, sea-butterflies have a density close to that of water (containing much water as gelatinous organisms) and they are very small (less than 2cm). Indeed, the more an organization is small, the more the surface / volume ratio is high and the greater the friction forces that apply to it are large, which helps to reduce the sedimentation rate.

> Their foot has taken the form of two wing-like lobes, or parapodia, which propel this little animal through the sea by slow flapping movements.

> To avoid detection by predators, sea-butterflies must be invisible. The shell and the body are totally transparent except a little part; the nucleus which is orange and includes the « heart ».

> For their feeding, they secrete a mucus net. It pastes particles in suspension in the water, then they ingest and digest it.

The gastropod above is called Venus shoe (« sabot de Vénus » in french) because of the shoe shape of the shell. You can find it on beaches, and it was the origin of the story of Cinderella’s glass slipper.

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