Wind sailors of the sea

Have you ever walked along the beach and encountered a fleet of bluish mussels on the shore? They are in fact not mussels but hydrozoans, famously known as by-the-wind sailors.  

Although physically similar with the Portuguese man o' war, this is not a jellyfish. Scientifically called Velella velella, it is the only known species under the genus of free-floating hydrozoans. It is found worldwide in both tropical and temperate waters. With a deep-blue rectangular float and an upright triangular sail, it looks like a miniature sailboat, on which its name was coined. 

This colonial species is made up of clustered polyps/zooids categorized into two types: gastrozooids and gonozooids. Gastrozooids function for plankton feeding using its tentacles (see photo above), while gonozooids have a reproductive function, that is, to constantly release medusa to the open waters. Having no means of locomotion, they are at the mercy of the wind to move around the seas and are thus, prone to mass-strandings on coastal beaches.

To know more about the by-the-wind sailors, visit SeaLifeBase.

If you have other information on them, you can e-mail us at sealifebase@fin.ph or come be a collaborator.

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Source: Monterey Bay Aquarium (MBARI). See page link here.Photos by Christian Coudre.
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