Can't find QtMultimedia on my Ubuntu installation of Qt

Hello,
I have an installation of QtCreator 3.5.1 and Qt5-default on my Xubuntu laptop. Th Qt version is 5.5.1

I have a Qt project I dug out on my Windows 7 laptop (had not touched it for a year).
It was developed using Qt Creator 3.1.2 (based on Qt 5.3.1)
In this project I need to access a webcam to take pictures. The project file has
QT += multimedia multimediawidgets
It seems to work fine,

but when I try to port the project to my Xubuntu laptop QtCreator tells me that multimedia is an unknown module.

Is there anyway to fix this?

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Added after 22 minutes:

Under Ubuntu I need to install a separate package qtmultimedia5-dev
(I also installed the corresponding doc and dbg packages)